16117 74TH PL W.PDF111111111111
5945
16117 74TH PL W
ADDRESS: 16,147
TAX ACCOUNT/PARCEL NUMBER:
BUILDING PERMIT (NEW STRUCTURE):
COVENANTS (RECORDED) FOR:
CRITICAL AREAS:
DISCRETIONARY PERMIT #'S:
DRAINAGE PLAN DATED:
PARKING AGREEMENTS DATED:
EASEMENT(S) RECORDED FOR:
PERMITS (OTHER):
DETERMINATION: ❑ Conditional Waiver ❑ Study Required ❑ Waiver
PLANNING DATA CHECKLIST DATED:
SCALED PLOT PLAN DATED:
SEWER LID FEE $:
SHORT PLAT FILE: LOT:
SIDE SEWER AS BUILT DATED:
SIDE SEWER PERMITS) #:
GEOTECH REPORT DATED: /
STREET USE / ENCROACHMENT PERMIT #:
WATER METER TAP CARD DATED:
OTHER:
LID #:
BLOCK:
LATEMP\DSTsTomulStreet File Checklist.doc
#P20
Critical Areas Checklist CA File No: CM M10
Site Information (soils/ topography/ hydrolog�y] "�/V�getation)
1. Site Address/Location 1 U 1 1 � [ ' F� ,y �'
2. Property Tax Account Number: 0 0% 1 O 4- 0 O 0009 00
3. Approximate Site Size (acres or square feet): 'dI 2�7.�, •�2 �rCRE
4. Is this site currently developed? _ yes; k'n'o.
If yes; how is. site developed?
5. Describe the general site topography. Check all that apply.
Flat: less than 5-feet elevation change over entire site.
Rolling: slopes on site generally less than 15% (a vertical rise of 10-feet over a horizontal
distance of 66-feet).
Hilly: slopes present on site of more than 15% and less than 30% (a vertical rise of 10-feet
over a horizontal distance of 33 to 66-feet).
Steep: grades of greater than 30% present on site (a vertical rise of 10-feet over a horizontal
distance of less than 33-feet).
Other (please describe):
6. Site contains areas of year-round standing water: WO ; Approx. Depth:
7. Site contains areas of seasonal standing water: N 19 ; Approx. Depth:
What season(s) of the year?
8. Site is in the floodway N 4 floodplain AJ 0 of a water course.
9. Site contains a�geek or an area where water flows across the grounds surface? Flows are year-round?
Iy v Flows are seasonal? (What time of year? ).
10. Site is primarily: forested ; meadow ;shrubs ; mixed ;
urban landscaped (lawn, shrubs etc)
11. Obvious wetland is present on site: N 0
1. Plan Check Numbc-r, if apl
2. Site is Zoned?
3. SCS mapped soil type(s)?
14.
Critical
15. Site
For City Staff Use Only
icable? > 7
idicates Critical Area on site? 854 vi (n c9 ec o
din designated earth subsidence landslide hazard area?
DETERMINATION
STUDY REQUIRED WAIVER
#P20
�f
of EDCity of Edmonds
Development Services Department
Planning Division
Phone: 425.771.0220
41C. t gqo Fax: 425.771.0221
The Critical Areas Checklist contained on this form is to
be filled out by any person preparing a Development
Permit Application for the City of Edmonds prior to
his/her submittal of the application to the City.
The purpose of the Checklist is to enable City staff to
determine whether any potential Critical Areas are; or
may be, present on the subject property. The information
needed to complete the Checklist should be easily
available from observations of the site or data available at
City Hall (Critical areas inventories, maps, or soil
surveys).
Date Received: ,
City Receipt #:
Critical Areas File #:
Critical Areas Checklist Fee: $135. 0
Date Mailed to Applicant:
A property owner, or his/her authorized representative,
must fill out the checklist, sign and date it, and submit it .
to the City. The City will review the checklist, make a
precursory site visit, and make a determination of the
subsequent steps necessary to complete a development
permit application.
Please submit a vicinity map, along with the signed copy
of this form to assist City staff in finding and locating the
specific piece of property described on this forma In
addition, the applicant shall include other pertinent
information .(e.g. site plan, topography map, etc.) or
studies in conjunction with this Checklist to assistant staff
in completing their preliminary assessment of the site.
The undersigned applicant, and his/her/its heirs, and assigns, in consideration on the processing of the application agrees
to release, indemnify, defend and hold the City of Edmonds harmless from any and all damages, including reasonable
attorney's fees, arising from any action or infraction based in whole or part upon false, misleading, inaccurate, or
incomplete information furnished by the applicant, his/her/its agents or employees.
By my signature, I certify that the information and exhibits herewith submitted are true and correct to the best of my
knowledge and that I am authorized to file this application on the behalf of the owner as listed below.
SIGNATURE OF APPLICANT/AGENT
DATE
Property Owner's Authorization
By my signature, I certify that I have authorized the above Applicant/Agent to apply for the subject land use application,
and grant my permission for the public officials and the staff of the City of Edmonds to enter the subject property for the
purposes of inspection and posting attendant to this application.
Owner/Applicant:
'S:JtFFA �tJ ;o E{ N 5
Name
Street Address �. W
_pMQNQ�2 1%011IV%
City State Zip
Telephone: 4 2,6 44 S & 5 7 (P
DATE 3 1 C,J
Applicant Representative:
Name
r2 0
Street Addre s
City State Zip
Telephone:
Email address (optional): Email Address (optional):
CITY OF EDMONDS
CRITICAL AREAS RECONNAISSANCE REPORT
Site Location: 16117 74th Place West Tax Acct. Number: 00544600001200
Determination: Study Required Determination #: CRA-2008-0034
Applicant: Stephen Johnson Owner: Kristin Hansen
CRITICAL AREAS RECONNAISSANCE REPORT: STUDY REQUIRED
During review and inspection of the subject site, it was found that the site contains and/or is
adjacent to critical areas, including Geologically Hazardous Areas, pursuant to Chapters 23.40 and
23.80 of the Edmonds Community Development Code (ECDC).
Part of the Lorian Woods Planned Residential Development (PRD-1989-1), the subject parcel
slopes east -west at approximately 35%, according to the City's LIDAR data. This qualifies as an
erosion hazard. There is a small area adjacent to the northeast corner of the parcel with slopes in
excess of 40%, which qualifies as a potential landslide hazard.
GENERAL CRITICAL AREAS REPORT REQUIREMENTS
Critical Areas Reports identify, classify, and delineate any areas on or adjacent to the subject
property that may qualify as critical areas. They also assess these areas and identify any potential
impacts resulting from your specific development proposal. If a specific development proposal
results in an alteration to a critical area, the critical areas report will also contain a mitigation plan.
You have the option of completing the portion of the study that classifies and delineates the critical
areas and waiting until you have a specific development proposal to complete the study. You may
also choose to submit the entire study with your specific development application.
• Please review the minimum report requirements for all types of Critical Areas that are listed
in ECDC 23.40.090.D. There are additional report requirements for different types of
critical areas (see below).
• Note that it is important for the report to be prepared by a qualified professional as defined
in the ordinance. There are options on how to complete a critical areas study, and there is
an approved list of consultants that you may choose from. You may contact the Planning
Division for more information.
• General Mitigation Requirements for all Critical Areas are discussed in ECDC 23.40.110
through 23.40.140.
STUDY REQUIREMENT — EROSION HAZARD AREA
It appears that this property contains or is adjacent to an Erosion Hazard Area. Erosion Hazard
Areas include:
• Those areas with Alderwood and Everett series soils on slopes of 15 percent or greater.
Any area with slopes of 15 percent or greater and impermeable soils interbedded with
granular soils and springs or ground water seepage.
• Areas with significant visible evidence of ground water seepage, and which also include
existing landslide deposits regardless of slope.
DEVELOPMENT PROPOSALS ASSOCIATED WITH EROSION HAZARD AREAS
Development within an Erosion Hazard Area must meet additional criteria.
• For erosion hazard areas with suitable slope stability, the only critical area study needed is
an erosion and sediment control plan prepared in compliance with the requirements set
forth in Chapter 18.30 ECDC as part of the construction documents. This option is at the
director's discretion, per Edmonds Community Development Code section 20.80.050.G.
• In areas where the slope stability is not suitable, projects within Erosion Hazard Areas will
require a report by a licensed Geotechnical Engineer or other qualified professional. Note
that it is important for the report to be prepared by a qualified professional as defined in the
ordinance.
• Report requirements are given in ECDC 23.80.050, and more generally in ECDC
23.40.090. D.
• Development standards are given in ECDC 23.80.060 and 23.80.070.
STUDY REQUIREMENT — LANDSLIDE HAZARD AREA
It appears that this property contains or is adjacent to a Landslide Hazard Area.
• A Landslide Hazard Area is any area with a slope of forty percent (40%) or steeper and
with a vertical relief of ten (10) or more feet (except areas composed of consolidated
bedrock).
• Landslide Hazard Areas are further defined and illustrated in ECDC 23.80.020.8.
• In addition to the general requirements for Critical Areas reports referenced above, specific
Critical Area report requirements for Landslide Hazard Areas are provided in ECDC
23.80.050.
DEVELOPMENT PROPOSALS ASSOCIATED WITH LANDSLIDE HAZARD AREAS
Development is restricted within a Landslide Hazard Area and its buffer.
• Projects that will intrude into these areas will require a report by a licensed Geotechnical
Engineer.
• The criteria that are applied depend on the amount that the buffer is reduced.
• The buffer can be reduced to a minimum of ten (10) feet (with an additional 15' building
setback per ECDC 23.40.280) if a report is prepared that meets the standards listed in
ECDC 23.80.050. The alteration must also meet the requirements listed in ECDC
23.80.060.
• In addition, proposals to reduce the buffer to less than ten (10) feet must comply with the
design standards listed in ECDC 23.80.070.A.3.
ALLOWED ACTIVITIES
Certain activities are allowed in or near critical area buffers as specified in ECDC 23.40.20. If you
have any questions about whether your proposed development qualifies as an allowed activity,
please contact a Planner for more information.
EXEMPT DEVELOPMENT PROPOSALS
Certain development proposals may be exempt from Critical Areas Requirements (ECDC
23.40.230). If you think that a specific development proposal may be exempt, contact a Planner
for more information.
Name Signature ' Date
NOTE: Cited sections of the Edmonds Community Development Code (ECDC) can be found on
the City of Edmonds website at www.ci.edmonds.wa.us.
3
LZI
i
_Exhibit 6
TERRA ASSOCIATES Inc.
WA
Consultants in Gebtechnical Engineering, Geology
and
Environmental Earth Sciences
& //7- 7 111`1v
Project T 840-1
June 6,1989
Robert and Joann Anderson
7370 North Meadowdale Road
Edmonds, Washington 98020
Subject: Geotechnical Report
Meadowdale Beach, Lots 54 to 57
Edmonds, Washington
Dear Dr. and Mrs. Anderson:
We have completed the geotechnical studies you authorized for your property in the
Meadowdale area of Edmonds. The site location is shown on the Vicinity Map, Figure 1.
The tract, referred to herein as the Anderson property, includes Lots 54, 55 and 56 of the
Plat of Meadowdale Beach and most of Lot 57. We understand that you intend to
subdivide this property into approximately ten lots for single-family residences. A final
plat has not been developed at this time.
The purpose of the present study is to assess landslide hazards on the property and
provide general recommendations for site improvements, and for grading, drainage and
foundations for residential. construction. The work completed. includes 1) a review of soil
reports and other information in City files, 2) examination of air, photos of the site
vicinity, 3) a visual examination of the property, including shallow soil explorations made
by hand, and 4) exploration of subsurface conditions using test borings and test pits. This
report describes our findings and summarizes our recommendations.
After the property has been subdivided, the City may require a geotechnical evaluation of
the construction proposed for each individual lot. Such work is not within the scope of
the present study.
SUMMARY.
The existing site topography and a possible plat with ten lots is shown on Figure 2. The
property slopes downward from east to west. The central portion of the site includes a
relatively flat bench. The steep slopes at the east side extend beyond the property line. A
lower bench occupied by several residences lies beyond the west property line.
15301 N.E. 90th Street • Redmond, Washington 98052 • Phone (206) 881-5570 • FAX No. 869-9173
Mailing Address: P.O. Box 3338,• Redmond, Washington 98073
Robert and Joann Anderson Project T-840-1
June 6, 1989 Page 2
The Anderson property is part of a large ancient landslide. The area that failed extends
along 75th Place West from Meadowdale County Park southward to about the 165th
block and from the bluff on the east to the shoreline. The original landslide probably
occurred several thousand years ago. Parts of this landslide have been active into recent
times and possibly are still active. The records indicate that landslides occurred in
Meadowdale during the winters of 1946-47, 1955-56 and during the 1960s and 1970s.
Local residents report that no detectable earth movements and .no building damage
occurred on the Anderson property during any of these events.
In 1979, the 40-year record of landslide events in the Meadowdale area was studied by
Roger Lowe Associates Inc and the landslide hazards were evaluated. Several possible
landslide categories were identified, based largely on topographic features existing at the
time of the study. A map that identified the landslide hazards and estimated failure
probabilities was developed for the entire Meadowdale area.
The Lowe study identified three categories of potential landslides on the Anderson
property, as summarized on Figure 3. Most of the property. where the subsoils are
believed to be ancient landslide debris was classified as previously failed material
susceptible to renewed landslide movements. On the central bench, the probability that
landslides of this type (4A) `might occur within 25-year periods was estimated at' 25
percent, the lowest rating given any area believed to be located on the old slump material.
This relatively low rating was given because no landslides have occurred on the bench
during historic times.
The western slopes below the bench were rated at 35 percent, only slightly higher than the
25-percent rating given the bench.
Because areas on the Anderson property at the northwest and the southwest corners were
believed to have been affected by three major landslides since the 1940s, The Lowe report
assigned these areas a rating of 90 percent. However, because residents on property
adjacent these comers of the Anderson property report that no damage to buildings and
no perceptible earth movements occurred during these events, the rating of 90 percent
assigned these areas likely was unwarranted.
The steep slope east of the bench was mapped as generally undisturbed materials
susceptible to shallow debris slides (3B) and to avalanches from further up the slope (2C).
A relatively low probability of occurrence was assigned to landslide events of these types.
The Lowe report recommended groundwater control as likely the most economical
measure for landslide risk reduction. Consequently, in 1980 through 1985, sanitary
sewers, storm sewers, and subsurface interceptor drains were installed around and within
the Meadowdale landslide. Interceptor Drains lA and 1B were installed on the Anderson
property at the locations shown on Figure 2. Since that time, a lowering of the
groundwater table throughout the landslide mass has been documented.
ano
Robert and Joann Anderson —
June 6, 1989
Project T-840-1
Page 3
In 1985, GeoEngineers, Inc evaluated the effects of the improved surface and subsurface
drainage and concluded that the probability of landslide occurrence had been reduced in
much of the area believed to be most susceptible to failure. On the Anderson property,
the estimated probability that the old slump material might move again within a 25-year
period was reduced by a'factor of about three.
Based on our test pits and borings and other available information, we conclude that all
the Anderson property below the bluff is underlain by landslide debris, mostly loose sands
mixed with silts, clays and buried vegetation, including trees. The depth of the debris
probably exceeds 60 feet under the central bench and likely is in the range of 30 to 40 feet
at the west property line.. Figure 4 summarizes our conclusions concerning generalized
subsurface conditions on the site.
Figure 4 also illustrates ground water conditions on the site observed during our field
work, which was performed during winter months. The water table appears to be about
five to six feet below the ground surface along the west property line but near the ground
surface on the slopes to the east. On the bluff, springs were observed where sandy soils
outcrop above fine-grained materials.
Based on these observations and our professional judgment, we agree generally with the
landslide hazards assessment in the Lowe report. Figure 5 summarizes our assessment of
present landslide hazards on the Anderson property and shows landslide occurrence
probabilities consistent with the latest evaluation by GeoEngineers, Inc.
In our opinion, Figure 5 is not adequate for assessing risk at individual residential lots.
Firstly, the probabilities appear to apply only to the large-scale slumps that were the Lowe
report's primary concern. In our opinion, while the low probabilities presented for the
areas on the eastern slopes are believed to be suitable for large-scale slumps, they may
underestimate the average occurrence intervals of the small-scale slides and avalanches
that typically occur on steep ground.
Secondly, available evidence suggests that most of the residences within areas supposedly
affected by the landslides of record withstood those events with little or no damage.
Consequently, probabilities of landslide occurrence, as presented in the Lowe report,
probably exaggerate .the risk of landslide damage to individual residences.
Figure 6 presents a risk assessment that we believe is applicable to individual residential
lots on the Anderson property. The probabilities presented are intended as measures of
the risk of landslide damage rather than landslide occurrence. On Figure 6, the
30-percent ratings on Figure 5 at the northwest and the southwest comers have been
reduced, reflecting the reports of local residents that the landslides responsible for the
30-percent ratings caused no perceptible earth movements on the Anderson property and
no damage to residences adjacent these areas.
Robert and Joann Anderson Project T-840-1
June 6, 1989 Page 4
In our opinion, the present risk is low enough to justify development of the Anderson
property, provided the design and construction procedures -used do not impair the present
stability, and provided also that future property owners are properly informed of the
landslide hazards that exist, as required by the City's Ordinance 2661, and accept full
responsibility for them.
In order to develop the property without increasing the risk of landslide damage on
adjacent property, and without unreasonable risk to the proposed residences, we
recommend that certain measures be incorporated in the construction proposed for each
lot. These include:
1) Homes should be adapted to the present topography, using split- and
multi -level construction where suitable.
2) Where slopes are steeper than 15 degrees, fill should not be placed under the
building footprints. Ground floors above the present grade should be framed over crawl
spaces.
3) Slab -on -grade ground floors may be used in cuts, and on fills placed on
slopes flatter than 15 degrees.
4) Basement cuts should not exceed about eight feet in height. If deeper cuts
are required on steep slopes, the basement should be stepped and the excavation
terraced.
5) Basement walls and perimeter foundation walls should be .designed for
lateral soil stresses suitable for the backslope angles.
6) Because landslide debris may provide relatively uneven support for
foundations, buildings should have conventional wood -framed construction supported on
reinforced concrete foundations. Concrete masonry is not recommended and brick
veneer should be used only in small panels.
7) In general, conventional spread foundations may be used. Home sites where
landslide 'debris is expected to provide poor bearing conditions should be explored with
test pits before final plans are prepared.
8) Setbacks from both ascending slopes and descending slopes should comply
with the requirements in the Uniform Building Code.
9) Pile and pier foundations may be considered as a means for improving
foundation performance where soils are poor, and to satisfy setback requirements.
10) Landscaping should preserve the existing topography to the extent practical.
Fills should not be placed on slopes steeper than 20 degrees. Fill slopes should be graded
not steeper than 25 degrees.
Robert and Joann Anderson / Project T-840-1
June 6,.1989 Page 5
11) Cuts should be limited to heights of about eight feet. Cuts up to four feet
may be supported by rockeries. Higher cuts should be supported with reinforced concrete
retaining walls.
12) Site drainage should be improved by installing drain rock bedding and
perforated drain pipe in the trenches with all new storm sewers, as was done in the LID
210 storm sewers.
13) Home owners should improve drainage on their lots by diverting surface
water into the storm water system. Perforated drain pipes tightlined to the storm sewers
should be provided around all perimeter foundation walls and basement walls and behind
all retaining walls. Rain gutters should discharge to the storm sewers in tightlines
different from those used for the foundation drains.
The following sections of this report discuss our findings and present our conclusions and
recommendations in greater detail. Our report has been prepared specifically for, this
project. It is intended for the exclusive use of yourselves and your representatives. Our
work has used methods and procedures consistent with local foundation engineering
practices. We provide no other warranty, expressed or implied. We do not guarantee
project performance in any respect, only that our work meets normal standards of
professional. care.
SITE SURFACE CONDITIONS
The project site is located south - of North Meadowdale Road and east of the 74th Place
West right-of-way in the Meadowdale area of Edmonds, Washington. The Anderson
property includes Lots 54, 55 and 56 of the Plat of Meadowdale Beach and part of Lot 57.
In plan it measures about 350 feet by 650 feet and includes approximately 5.3 acres. The
Anderson residence is located on Lot 55 in the west center of the site.
As shown on Figures 2 and 4, the eastern third of the property is a slope that gradually
steepens toward the east. The upper slope climbs steeply to a bluff with its crest near
Elev 250 to 300 off the site to the east. At the time our study was performed, two small
surface sloughs were noted on these steep eastern slopes.
The central area of the property is a bench about 100 to 120 feet wide covered with grass,
ivy and scattered trees. Grades on the bench vary from about Elev 120 in the north to
Elev 150 in the south. The Anderson residence and a shed to the south are located on
this bench. Several firs up to 47 inches in diameter and other large trees, straight-trunked
and vertical, are located just south of the house.
To .the west the bench slopes down to the 74th Place West right-of-way. The grade
change from the bench to the west property line ranges from ten feet at the north to about
50 feet at the south. Typical slope inclinations are in the range of 20 to 25 degrees with
local areas as steep as 45 degrees.
Robert and Joann Anderson —
June 6,1989
Project T-840-1
Page 6
In 1984, as part of the LID 210 work completed by the City, Interceptor Drains 1A and 1B
were installed on the Anderson property, approximately as shown on Figure 2.
At the time of our study, many areas of the property, especially the east slopes, were wet
from snow melt, rainfall, seepage and springs. Surface water not collected by the
interceptors descends to the bench, runs downslope in watercourses around the Anderson
home, then continues on to. catch basins and other drainage features.
The central bench on the Anderson property extends off the site to the north, where it is
occupied by single-family residences. Other residences are located on a lower bench west
and south of the Anderson property. All of these structures are supported on the slide
debris that is part of the Meadowdale landslide complex.
We understand that prior to the construction of the Anderson residence in 1965, six
cabins and a house had been present on the Anderson property for many years. When
these buildings were demolished in 1963,.none are reported to have showed any evidence
of landslide damage.
REVIEW OF RECENT LANDSLIDE ACTIVITY
The original landslides in the Meadowdale area are believed to have occurred several
thousand years ago. The area involved extended from the bluff to the shoreline and from
Meadowdale County Park on the north southward to about the 165th block. Landslide
activity in this area has continued during historic time. The most readily accessible
records describe the landslide activity during only the most recent 40 years. The records
may not be complete.
The landslide records indicate that much of the ancient landslide south of the present
wharf was active in the winter of 1946-47. The same area is believed to have been active
again in the 1960s. The area affected extended more than 400 feet east of the railroad.
These events explain the 4A90 hazard rating the Lowe report gave the southwest corner
of the Anderson property, as shown on Figure 3. However, residents near the Anderson
property during these landslides report that no damage occurred on their property or on
the Anderson property during either event.
During the same winter of 1946-47, a slide that blocked North Meadowdale Road did
occur in the road cut on the Anderson property about 70 feet east of the present driveway.
This slide probably was not related to the other landslide activitythat occurred that
winter.
In the winter of 1955-56, landslides were reported at two locations north of North
Meadowdale Road. The Lowe report concludes that during that winter the active area
probably extended over most of the ancient landslide north of the wharf. These slides
explain the Lowe report's 4A90 hazard rating shown on Figure 3 for the northwest corner
of the Anderson property. However, residents near the Anderson property report that no
damage occurred on their property or on the Anderson property during that winter. .
Robert and Joann Anderson.
June 6, 1989
Project T-840-1
Page 7
Numerous other smaller landslides have occurred within the past 40 years, most of them
at the toe of the slope near the railroad. At least two larger slides were reported. In
1970, a slide just north of the wharf crossed to the east side of 75th Place West, causing
minor pavement disruption, which recurs periodically. In 1973, a slide near the 158th
block adjacent the railroad extended upslope to the west edge of 75th Place West.
On the Anderson property, the ancient landslide mass has not undergone perceptible
movements during the 40-year period of record. In addition, only minor sloughing has
been observed on the eastern slopes since the Anderson home was constructed in 1965.
Since that time, no avalanche debris has reached the toe of the slope at the east side of
the bench.
We reviewed stereoscopic air photos that show the property vicinity during the years 1947,
1955 and 1970. Pavement disruption on 75th Place West west of the property, due
probably to the 1970 slide noted above, 'can be seen on the 1970 photos. The 1955 photos
show bare soil on the eastern slope above Lot 57 off the Anderson property. This scar
probably was part of the residential construction going on at that time above the slope
crest.
FIELD EXPLORATION AND LABORATORY TESTING
Our field work on the Anderson property was performed on February 14 through 17,
1989. Subsurface conditions were explored by drilling two standard penetration test
borings to depths 50 and 69 feet below existing grades. In addition, six test pits were dug
with a backhoe to depths that ranged from 12 to 19 feet below existing grades.
The borings were made by Drilling Unlimited Inc of Olympia. A skid -mounted drill rig
was used for one boring and a truck -mounted rig for the second. Continuous flight,
hollow -stem augers were used to advance and support the boreholes.
The test borings and pits were located by measuring from site features shown on the
survey plan provided. us. The approximate locations explored are shown on Figure 2.
Ground surface elevations reported for the locations explored were estimated by
interpolating contour lines shown on the survey plan.
The field exploration was continuously monitored by an engineering geologist from our
firm. A log was prepared for each boring and test pit. The soils observed were classified
in general accordance with the system described on Figure 7. Logs of the borings and pits
are presented on Figures 8 through 15. These logs report our interpretation of the field.
logs and reflect the results of laboratory examination and testing of the field samples.
In each boring, standard penetration tests were performed at selected intervals by driving
a sampler with a two-inch outside diameter using a 140-pound hammer falling 30, inches.
The results of these tests are the N-values reported on the boring logs.
Robert and Joann Anderson
June 6, 1989
Project T-840-1
Page 8
Representative soil samples were placed in closed containers and taken to our laboratory
where they were again examined. The field moisture content of each sample was
measured. Field visual classifications were checked by running Atterberg tests and sieve
analyses on selected samples. All the test results are recorded on the boring logs.
Ground water observation wells were installed in both borings. .
r'
SUBSURFACE CONDITIONS
The locations explored on the Anderson property are shown on Figure 2. The following
discussion is general in nature. For more specific information regarding conditions
observed at the locations explored, refer to the logs of borings and test pits, Figures 8
through 15. ,
Boring 1 at the south end of the central bench was drilled to a depth 50 feet below
existing grade. The soils observed are mostly loose silty fine to medium, sands mixed with
clays and silts.
Based on the relatively low N-values-in Boring 1, as reported on the log, and the mixed
appearance of the material, we believe that all the soil is landslide debris derived from
the Esperance and Whidbey formations exposed on the bluff to the east. The base of.the
ancient landslide is at an undetermined depth below the bottom of the boring.
Boring 2 at the north end of the central bench encountered about 30 feet of loose sandy
soil with chunks of clay and wood debris, similar, to the soils recovered in Boring 1. Below
the 30-foot depth, silts and clays were encountered, generally very stiff but becoming hard
within the final eight feet of the borehole.
Subsurface conditions in Boring 2 are similar to conditions reported by Lowe for a
borehole about 150 feet northwest of Boring 2. The upper 30 to 50 feet is slide debris.
The deeper clays and silts are believed to be part of the Whidbey formation and may or
may not be part of the ancient landslide.
All the test pits on the Anderson property encountered slide debris: loose silty sands with
chunks of stiff to hard clays and silts. Trees buried in slide debris were uncovered in Test
Pits 2 and 4. No, stratification similar to that in the undisturbed Esperance sands near the
top of the bluff was observed in any of the pits.
Test Pits 2 and 4 through 6, which were excavated on the eastern slope, encountered
ground water at shallow depths well above the toe of the slope. The sidewalls in Test Pits
2 and 4 collapsed as the pits were being dug.
A ground water observation well installed years ago by the City is located near the
southwest corner of the property. A log of the borehole is not available. We understand
from discussions with the geologist who installed the well that the depth of the boring is in
the range of 24 feet and all the material drilled was landslide debris. At the present time,
the water level in this well is five to six feet below the ground surface.
Robert and Joann Anderson Project T-840-1
June 6,1989 Page 9
With the possible exception of the Whidbey hard clays in the bottom of Boring 2, intact
native soils were observed on this site only at fresh exposures on the bluff at the east
margins of the property. Figure 4 shows a generalized profile of the native soils and the
overlying landslide materials. Near the toe of the bluff,- both native soils and ancient
landslide debris are covered with slope wash and avalanche debris deposited since the
original landslide. As noted above, in Test Pits 2 and 4, trees were observed buried in
debris.
The Whidbey formation is exposed on the bluff above the debris. In some areas near
Elevs 170 to 190, the Whidbey soils are pebbly silts and sands. Further up the bluff, the
Whidbey soils are finer, mostly silts and clays with seams of fine sand. .
The Esperance sands of the Vashon glaciation lie above about Elev 220 to 230. There are
springs at the contact between the Esperance sands and the underlying Whidbey clays.
PRESENT LANDSLIDE HAZARDS
The Anderson property lies within the boundaries of the Meadowdale landslide studied in
1979 by Roger Lowe Associates, Inc. The purpose of that study was to assess the various
landslide hazards present in different areas and evaluate the risk that a landslide event
might occur.
The Lowe report classified three categories of possible landslides on the Anderson
property, as summarized on Figure 3:
1) avalanches of debris from the steep slope at the east side of the'site (2C);
2) landslides on the east slope in material that has never before failed (313); and
3) renewed movements of the ancient landslide materials beneath the central
bench and the western slopes (4A).
The first two categories were considered to have relatively low risk, only a two to f ve
percent chance of occurrence within a period of 25 years. The possibility that a failure in
the third category would occur within 25 years was estimated to be about 25 percent on
the central bench and 35 percent on the western slopes.. Because major landslides that
occurred in 1946-47 and in 1955-56 were believed to have extended onto the Anderson
property, small areas at the northwest comer and the southwest corner were assigned a 90
percent chance of failure within periods of 25 years.
The Lowe report concluded that a reduction of ground water levels in the landslide
complex likely was the most effective means of reducing the risk of additional landslides:
Consequently, during the early 1980's, the City installed sanitary sewers, storm sewers, and
subsurface interceptor drains at various locations on and around the Meadowdale
landslide. Interceptor Drains 1A and 1B were installed on the Anderson property at the
locations shown on Figure 2.
Robert and Joann Anderson Project T-840-1
June 6, 1989 Page '10
In 1985, GeoEngineers Inc evaluated the effects of these new drainage facilities and
concluded that the landslide hazard had been significantly reduced in many areas that had
high risk. Landslide occurrence probabilities of 90 percent in 25 years were reduced to 30
percent in 25 years. Similarly, ratings of 25 and 35 percent in 25 years were reduced to 10
percent in 25 years.
Our explorations on the Anderson property disclosed subsurface conditions generally
consistent with the landslide categories described in the Lowe report (see Figure 3).
However, when applied to more localized areas, these categories are not always
descriptive of the landslide processes actually occurring or most likely to occur. For
example, in the steep areas on the bluff where undisturbed soils occur, the Lowe report
distinguishes between slumps (3A) and more shallow slides (3B). However, on the old
landslide debris west of the bluff, all the recent and the anticipated landslide activity was
classified as renewed slump movements (4A). although much of the recent activity was
recognized as having characteristics of relatively shallow earthflows or debris slides.
Figure 5 presents a landslide hazard map for the Anderson property that we believe
better describes the slope movements that could occur. It retains the general features of
the Lowe report map but has been adjusted to better fit local geology, topography and
drainage conditions.
On the steep bluff at the east margin of the property, the Lowe report indicates that
slumps (3A) may occur in the exposed Esperance sands, but are unlikely. The probability
of such failures is low because the springs on the bluff provide much better drainage for
the sands than existed at the time the ancient landslide occurred. Nevertheless, the overly
steep face of the bluff is constantly being loosened by weathering and plant growth.
Shallow surface slides result from these processes. They usually are small in area and of
little consequence for construction further down the slope since downslope movement of
the debris commonly is hindered by vegetation on the lower slopes. On Figure 5, to
distinguish these shallow slides from more massive slumps (3A), we have used the Lowe
report category 3B, debris slides in material that has not previously failed.
As shown on Figure 4, the Whidbey formation is exposed on the steep eastern slope
below the Esperance sands.. On Figure 5, this area is the. second zone west of the east
property line. The Lowe report indicates that shallow debris slides (3B) .are expected as
weathering and plant growth gradually loosen this material. This zone is also at risk due
to avalanches of debris from the Esperance sands above (2Q. A massive slump (3A) is
also possible. However, for the present drainage conditions and bluff topography, a
slump would likely, be confined to the overlying Esperance sands.
The third zone from the east property line is below the zones where undisturbed native
soils are exposed, but 'upslope from the ancient landslide debris (4A). The near -surface
soils are colluvium from the bluff (see Figure 4). Due to surface water from the springs
on the bluff, the ground water table is near the ground surface. The landslide hazards in
this area are shallow slides in steeper, wetter zones of colluvium (4B) and avalanches
from slides occurring higher up the slope (2Q.
P'
Robert and Joann Anderson
June 6, 1989
Project T-840-1
Page 11
The fourth zone from the east property line on Figure 5 is the lower slope at the east side
of the central bench. This zone and the remainder of the property to the west are
underlain by ancient landslide debris. The east boundary of this zone approximates the
trace of the old failure plane on the present ground surface (see Figure 4). The landslide
hazards include avalanches off the slopes to the east (2C) and renewed activity of the old
slump debris (4A). There is an additional risk of shallow slides in the old slump debris or
in colluvium that has accumulated since the ancient landslide occurred (Q). These latter
failures are most likely to occur on the steeper slopes to the north during unusually wet
winters.
The remainder of the site includes the central bench and the slopes to the west. The,
major landslide hazard in this area is renewed activity in old slump debris (4A). In
addition, the east side of the bench may receive avalanches. from the slope to the east
(2C). There is little chance such an avalanche would carry across the bench and down the
western slopes. However, the west side of the property has locally steep debris slopes
where shallow slides (413) may occur during unusually wet weather.
The west corners of the site are classified in the Lowe report as having the highest
landslide risk on the Anderson property. These areas also have risks due to landslide
hazards other than renewed slumps, as shown on Figure 5.
A numerical probability of occurrence is presented on Figure 5 for the multiple hazards in
each of .the various areas. The probabilities shown are consistent with those in the Lowe
report, as modified by the 1984 assessment by GeoEngineers, Inc.
In our opinion, the landslide occurrence probabilities shown on Figure 5 for the central
portion of the property are reasonable considering the historical record of fairly
large-scale landslide events. The 10-percent rating has been assigned arbitrarily to areas
where renewed movements of the old slump material have not been reported and are not
believed to have occurred within historic. times. The bench on the Anderson property is
such an area.
Applying the conclusions of the Lowe report elsewhere on the Anderson property
presents some difficulties. Firstly, the 30-percent rating was given the west comers of the
Anderson property because these areas were believed in the Lowe report to have been
affected by landslides in the 40-year record. However, downslope neighbors of the
Anderson property who lived through those events report that no perceptible slope
movements occurred on their property or on the Anderson property during any landslide
of record. Consequently, the original 90-percent ratings, and the current 30-percent
ratings, probably are too conservative, based on the available evidence.
Secondly, with regard to the eastern slopes, landslide occurrence probabilities in the
range of only two to five percent, as assigned by. the Lowe report (see Figure 3), are
understandable only as estimates of the chance that a large-scale event in the native,
undisturbed bluff soils might occur. We agree that the probability of large-scale slumps of
Robert and Joann Anderson
June 6,1989
Project T-840-1
Page 12
the bluff is low, as predicted by Figure 3. However, we believe these low pond caused
babilities
underestimate the frequency, of small-scale landslide events in overly ound water. Such events$ t steep small in scale,
by weathering, erosion, and excessive g?located on the de area or in the path of
could cause significant hazards for residences
an avalanche.
A third difficulty in applying the Lowe report to residentiallots
isi that
prences, ba l tiesth f
landslide occurrence may not represent the risk of damage o
primary concern of home owners. The historical recorrdd t a have owdale ind icates all the homes
few
homes have actually been damaged by the landslides
within a defined landslide area were not damaged bha e landslides pobabil probability occurred,
landslide
probability of residential damage must be less t P and
occurrence. Unfortunately, the relationship between a lace tto place. e Moreovedsltldhe
occurrence cannot easily be evaluated and vanes from p
probability that a landslide will damage homes
ill ilanide will occur rencrease as mains de constant. homes
increases, even though the probability that the
A qualitative risk assessment that incorporates the considerations above is show our
on
Figure 6. We recommend its use ntral bench, which wer residenti,al lots on the Anderson property.
do not believe has experienced
opinion, the risk is lowest on the central
any landslide activity during the 40 years of record. less than five percent in 25 years,
believe the probability of landslide damage likely
on a landslide occurrence probability of ten percent, as shown on Figure 5.
ence
On the western slopes, the risk is higher than on the bench, due primarilyVh° the
r Tana landslide
of locally steep slopes, and to the proximity of downslope areasg
occurrence probabilities.
The risk at the toe of the eastern slopes, in our opinion,
debris and to avalanches off the
due to the threat of small slides of overly wet slop
steeper slopes to the east. Slides in the debris on the he recent drainage impwer slopes Povementsarently aand to
ve not
occurred during the 40 years of record. Due tot owners,
the additional drainage improvements that will ee oe��e�e. re home Slldes off the upper
frequency of occurrence of such slides is not expected are
slopes that might cause avalanches on the lower slopes
s apparently
pll r Aland to hindrance with an the
average return period of ten to 20 years. Due to their
avalanches have reached the lower slopes during the
heavily vegetated lower slopes, no
past 30 years.
In our opinion, residences located on the upper slopes would be closer to potential
erience
eater risk.
small-scale landslide activity and thus would. ielp to be selected as home sites.e these areas
are comparatively inaccessible, they are Y
C
Robert and Joann Anderson
June 6,1989
DISCUSSIONS AND RECOMMENDATIONS
eneral
Project T 840-1
Page 13
Figures 5 and 6 and the preceeding pages describe the landslide hazards and risks present
on various sections of the Anderson property. The hazards can be separated into two
general groups: 1) large-scale, relatively deep-seated slope movements caused by renewed
activity off the ancient landslide; and 2) small-scale, comparatively shallow slides. These
latter slides may be avalanches off the oversteepened bluff at the east margins of the site,
or slides in colluvium that have accumulated below the bluff.
Within the past 40-odd years, large-scale activity has not affected the Anderson property.
Moreover, the drainage system installed by the City under -LID 210 has improved the
large-scale stability and reduced the risk -that . a future large-scale event will affect the
property. At the present time, the probability of occurrence of a large-scale event is
believed to, be less than 30 percent in 25 years everywhere on the property, and in the
range of 10 percent in 25 years on the central bench, the western slopes and the lower
eastern slopes. In our opinion, the probability of landslide damage is significantly smaller
than these estimated probabilities of landslide occurrence, as illustrated by Figure 6.
The risk of a landslide activity, both large-scale and small-scale, is now low enough to
justify development of the Anderson property. This applies to all the lots shown on
Figure 2. Some lots have higher risk than others; but on all lots, the risk is small enough
to warrant development. On all lots, residual risks exist that cannot be eliminated. As
required by the City's Ordinance 2661, future lot owners should be fully informed
regarding the residual landslide risks, both large=scale and small-scale, and their purchase
agreements should require them to accept full responsibility for these risks.
While efforts to further reduce the risk of large-scale landslides, in our opinion,. are not
warranted, the risk from small-scale slides may be either increased or decreased,
depending on the construction on the individual lots. Lot owners should be held to
construction and maintenance standards that will reduce their risk as much as practical.
The paragraphs below in this section of the report describe recommended measures to
reduce the risk of small-scale landslides. These measures, however, will neither entirely
remove the hazard nor eliminate the risk.
Residences constructed most everywhere on the Anderson property will be supported on
old landslide debris. In general, conventional spread. foundations may be used. However,
our test pits indicate that on some building sites bearing conditions on the debris may be
relatively poor. Building supported on such _material should be expected to experience
small settlements. Consequently, in our opinion, the Anderson property is best suited for
wood -framed construction with stiff exterior wall sheathing. Concrete masonry walls,
which can develop cosmetic damage with only small settlements, are not recommended.
Brick veneer should be used sparingly. Lot owners who wish to reduce the risk of
cosmetic damage caused by settlement may consider supporting their homes on pile or
pier foundations.
Robert and Joann Anderson
June 6,1989
Project T-840-1
Page 14
Working conditions on the Anderson property may be excessively wet during the winter
months, especially on the eastern slopes. We recommend scheduling all site work for the
drier months from April to October.
Site Improvements
In order to subdivide the Anderson property, only limited site improvements are
necessary. To provide access to the interior lots, the existing driveway must be extended,
approximately as shown on Figure 2. Either concrete or asphaltic pavement may be
supported on the landslide debris on the Anderson property. In either case, the subgrade
should be proofrolled to assure it is firm and unyielding. The uppermost twelve inches of
the subgrade should be compacted to 95 percent of its ASTM D 1557 maximum dry
density: Site soils may be too wet to achieve this level of compaction. In that case, a
clean bank -run gravel or crushed rock should be imported and a subbase constructed at
-least twelve inches thick.
Asphalt pavement should have a base course of crushed rock at least four inches thick
and a surface course of asphaltic concrete at least two inches thick. Concrete pavement
should be at least five inches thick. It may be placed directly on the subgrade, provided
the work is done in dry weather. A base course of crushed rock a few inches thick may, be
needed in wet weather.
We recommend extending the storm sewers to the end of the new driveway. This will .
provide an opportunity to install additional drainage at the toe- of the east slopes and
provide a place where lot owners can discharge their foundation drains and roof gutters.
The storm sewers should be tightlined. To pick up ground water seepage intercepted by
the trench, drain rock bedding and perforated drain pipe should be installed in the
excavations, as was done with the LID 210 storm sewers. The drain pipe should be placed
at the lowest invert practical. The trench should be lined with filter cloth and backfilled
with pea gravel, except within two feet of the surface.
Other utilities should be bedded and backfilled in accordance with AWPA standards. All
utility trench backfill should be at least moderately compacted. Under pavement, backfill
in utility excavations should satisfy the proofrolling and compaction recommendations
above.
Cuts and Fills
Residences and landscaping should be designed to fit the existing topography. Homes on
the relatively flat central bench may be conventional construction. If desired, fills up to
about three feet in depth may be used to raise grades. Foundations and slab -on -grade
ground floors may be supported on properly compacted fills.
Robert and Joann Anderson
June 6, 1989
Project T-840-1
Page 15
Homes built on sloping ground should be multi- or split-level, as suited to the present
topography. Basement cuts into the slope should not exceed eight feet in height. Deeper
basements should be terraced. Fills floors above not resent grades should be framed over crder homes on'slopes awl
er
than about 15 degrees. Ground p
spaces.
Cuts and fills in landscaped areas should be minimized. Cuts up to four feet high may be
supported by rockeries, provided high maintenance and a risk of failure is acceptable.
For higher cuts or where better performance is desired, reinforced concrete retaining
walls should be used. All retaining structures should have backfill drains near their
footings connected with tight lines to the storm water system.
Foundations
In general, wood -framed residential construction may be supported on conventional
spread foundations. However, because most of the property is underlain by landslide
debris, bearing conditions at some building sites may be relatively poor, especially on the
lower eastern slopes, where our test pits uncovered trees and other vegetation buried
within the debris.
Preliminary building plans, once prepared, should be reviewed to evaluate likely
foundation requirements. Following the review, exploration of the building site with test
pits may be recommended. Where needed, the pits should extend several feet below the
intended footing bearing grades. To provide suitable bearing for footings, unsuitable
materials, if found, should be removed to depths at least two feet below the, footings and
replaced with compacted gravel or rock fill.
Where buildings overhang slopes or are located closeto
slope
crests,
requirements,thef ions
should be stepped down to bear well below present grades.
described below, should be satisfied. Where conventional foundations for such
applications are not practical, pier or pile foundations should be considered. Since these
piles likely will be supported entirely in debris, careful attention should be paid to
estimating design capacity.
Buildings supported on landslide debris may experience settlement due to the excessive
and variable compressibility of the debris. Home owners who wish to reduce the risk of
poor foundation performance may consider using pile or pier foundations to support their
residences. The use of these deep foundations will reduce the risk of damage caused by
settlements due to unsuitable bearing materials present at shallow depths. However,
deep foundations likely will not reduce the property
ture proide perty owners as
occurred
on the site. Consequently, deep foundations should not be viewedby p o
a means of reducing their risk of landslide damage.
Robert and Joann Anderson Project T-840-1
June 6,1989 Page 16
Setbacks From Ascending Slopes
In order to provide protection from slope drainage, erosion, and shallow failures, the
Uniform Building `Code requires that buildings be set back from ascending slopes.
Residences constructed on the central bench well away from the steep eastern slopes will
be exposed to very little risk of this type. However, building sites on the eastern slopes
may have only minimal setbacks and thus higher risks of damage caused by these
potential small-scale failures.
UBC requires a minimum setback of 15 feet. On slopes not overly steep, this requirement
can be satisfied by excavating a bench behind the residence and supporting the low . cut
with a retaining wall. On steeper slopes, the code's intent can be satisfied, in our opinion,
by constructing the foundation wall adjacent the slope to a -height where the top of the
wall is 15 feet from the face of the slope.
Since these small setbacks are catchment areas for debris sliding off the slopes above
these homes, where .the setbacks meet only the minimum UBC requirements, the rear
walls of the buildings, in our opinion, should be designed to withstand debris impacts.
Setbacks from Descending Slopes
For setbacks from descending slopes steeper than 18 degrees, we recommend complying
with the UBC requirement of 40 feet or one-third the height of the slope, whichever is
less. The slope height may be measured to the next lower bench of significant width.
Where it is desired to construct within the normal setback zone, the intent of the code, in
our opinion, can be satisfied by lowering the foundations. Where the slopes are high, pile
or pier foundations may be necessary.
Basement and Foundation Walls
Because homes on the Anderson property will be supported on old landslide debris,
foundation bearing conditions may be relatively poor. Building settlements that vary from
place to place should be expected. In order to reduce the risk of poor foundation
performance that may result from these variable settlements, we recommend using only
cast -in -place concrete foundation walls and basement walls, properly reinforced.
In general, residences on sloping sites should be stepped to fit the present topography.
Basements are recommended since they will assure that many of the foundations will bear
well below finish outside grades. We recommend limiting basement cuts to a maximum
of eight feet. If a two -level basement is desired on a steep site, the basement should be
stepped to fit the slope so that a terraced cut can be made with each terrace not more
than eight feet high.
Robert and Joann Anderson Project T 840-1
June 6, 1989 Page 17
All basement walls and foundation walls should be provided with -perimeter footing
drains. The drains should consist of. a ,perforated pipe within an envelope of washed
stone, all enclosed -by filter fabric. The walls should be treated with dampproofing. A
drainage course should be placed outside the wall and connected to the footing drain.
This wall drain may be either free -draining gravel backfill or a manufactured drain
attached to the wall after the dampproofing has been applied.
Soil lateral stresses for structural design of foundation walls and basement walls .will
depend on the steepness of the backslopes and other factors and should be selected
specifically for each building site.
Site Drainage
At the present time, surface runoff, rainfall and seepage from the bluff and near -surface
ground water are collected on the eastern slopes by Interceptor Drains 1A and 1B. These
recent improvements have significantly dried up the Anderson property. Some water
undoubtedly passes under the drains and reaches the ground water. Since the water table
presently is well below the ground surface at the west property line, the present
large-scale stability of the Anderson property, in our judgment, is adequate to justify
subdivision of the property. - However, measures to improve site drainage can be obtained
at little premium cost by incorporating them into any storm sewer extensions that may be
needed, as discussed in the Site Improvements section above.
To reduce the risk of local, small-scale sloughing of steep slopes due to excessive surface
water and high ground water, other drainage measures should be installed as part each lot
owner's construction.
Each lot should be landscaped so that all surface water is collected and conveyed into
catch basins connected to the storm sewer system.
All basement, foundation, and retaining walls should be provided with perforated footing
drains, as described above. The drains should connect to the storm water system with
tight lines. Cleanouts should be provided.
Rain gutters should be connected to the storm water system using tight lines separate
from those used for basement drains.
Stability During Construction.
The present stability of sloping sites will be disturbed by construction activities on- the
individual lots and the risk of slope failures will be highest at that time. The risk is mainly
to builder's operations close to the disturbed area. Builders can minimize their risk by
using good construction practices. Surface water should be diverted into catch basins and
the site dried up prior to making any excavations. Excavation sidewalk should be sloped
back at safe angles or supported with temporary shoring. Where excavations encounter
ground water, perimeter ditches should be constructed to control the water.
Robert.and Joann Anderson
June 6, 1989
Project T-840-1
Page 18
Excavations on the individual lots may create hazards on adjacent lots, depending on how
the buildings are sited and on the construction sequence for adjacent buildings. Problems
of this type are unlikely, but should be considered on a lot -by -lot basis.
Since a slope failure in landslide debris initiated by an excavation on the Anderson
property would not progress upslope into native, undisturbed material, temporary
excavations will cause no risk for neighbors of the Anderson property.
Excavated materials stockpiled on steep slopes would place neighbors downhill at risk.
Excavated material for use as backhll should be stockpiled on gentle slopes where
adjacent property is not endangered. Surplus material should immediately be hauled off
the site.
Post -Construction Stability
In our opinion, the development of residential construction on the Anderson property will
not have adverse impacts on the landslide hazards that affect the Anderson property and
the neighboring property. Implementation of the drainage measures recommended
herein will lower the groundwater table and reduce the current risk of landslides on the
Anderson property and on the property downslope. Construction on the Anderson
property will not affect the stability of the bluff and thus will not adversely affect
neighboring property to the east.
Slope Ve etation
Maintaining healthy vegetation on slopes is important for controlling erosion and
reducing the risk from small-scale landslides. The _existing vegetation on steeper slopes
outside construction areas should be preserved to the extent practical. Trees that might
topple onto the buildings should be trimmed back but not removed. Catch basins and
storm drain lines should be kept clear of debris and free -flowing. During construction,
stripped soils should be covered with straw or otherwise protected to reduce erosion. All
landscaping around the residences should be installed as soon as practical after the
buildings have been completed.
CLOSURE
The analyses and recommendations submitted herein are based on data obtained from
test borings, test pits and visual observations of soil exposures. However, subsurface
conditions elsewhere on the site may differ from those observed at the locations explored.
The nature and extent of any such variations may not become evident before construction.
If variations are observed during construction, Terra Associates, Inc. should be requested
to evaluate the actual site conditions and review the recommendations in this report prior
to proceeding with the construction.
Robert and Joann Anderson Project T-840-1
June 6, 1989 Page 19
The following figures are included and complete this report:
Figure 1
Vicinity Map
Figure 2
Exploration Location Plan
Figure 3
Landslide Hazards from Lowe Report 1979
Figure 4
Generalized Geologic Cross -Section
Figure 5
Landslide Hazard Map
Figure 6
Residential Risk Map
Figure 7
Legend for Test Pits and Borings
Figures 8 through 15
Logs of Test Borings and Test Pits
We appreciate the opportunity to provide these services. Please contact us whenever we
may be able to assist you, and please call if you have any questions concerning our report.
Respectfully submitted,
TE ASSO TES, INC
Charles R. Lie
Engineering Geologist
i,�� Aw►�A ��
William Bailey
Project Manager
Anil Butail, PE
President
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�� r � :%l' Fr' 11 I1'•`�`.�•; ...4 `\ (I II k �i.
li aga��'!
R�_ ;� •- • r�I� \\ �.t` �il� I�:� III 1� $
1.
Ids i
s.
N. MEADOWDALE RD, `
1' M 14t•A•:• A4•'..Wr �rQT��
to
V�
1 'SG
"• f
y �'.----
LANDSLIDE HAZARDS j
I� \ ,25 �...- . ,
4A Renewed movements in old slump material A
2C Avalanches of encroaching landslide material `.�: ) ^ I • •� \ 1'` �l'0.
313 Debris slides in materials that have not ! • . i'; ti I J _ I �, _ ' I
previously failed
The two trailing digits indicate the estimated probability 3 02` ` l
i-
of occurrence, in percent, during a 25-year period � i 1 • " _
35.
a !
This figure copied from Fgure 5 in
the final report on the Meadowdale t ,/
Area Landslide Hazards Investigation , : i + i• ,I I I �j j
by Roger er Lowe Associates Inc,1979 J
—
i
( 1 D
l/ y
\g o
3802
j70
IN
MDERSON PROPER
4A25 4A 2
..
0 2 0 ^
�+ti,� `.� 4 • .,. , � � .. ,Il Lam. •19,1 I r, j ` C� ,
Scale. 1 - 300 2.1
/ J i/%/�C •/ '� '
4AV0
LANDSLIDE HAZARDS FROM LOWE REPORT
TERRA ANDERSON PROPERTY
::•. MEADOWDALE BEACH EDMONDS
ASSOCIATES
Geotechnical Consultants Proj. No. 840-1 Date 3/89 Figure 3
320
280
240
o2!
a 160 Approximate present grand water table
120
80
U41
B-1 (offset)
1 l '
Piez
set)
i
_ l '
Slump debris from ancient landslide
This figure is for illustrative purposes only. The subsurface
conditions shown are an interpretation of the conditions observed
in test borings and pits, and other available information. Variations,
may exist between actual conditions and the conditions shown.
Probable ancient failure plane
Ground lost since
the ancient larrcktlide Present grottrtd surface
• VASHON DRIFT
Spring lineEsperance Sands
CF
s.
WHDBEY FORMATION
Pebbly sands and sits .
\- Possible seepage zone
burled under colhrvium
Colluvium with buried. trees
(avalanche & slide debris)
TERRA U1--Nt2iP"x"' "t"`U`
ANDERSON f
ASSOCIATES MEADOWDALE BEAt
BOGeotechnical Consultants 1Proj.No.840--1FDate 3/
= sos.33•
�
ice.•. •tom �c'�; --�=�_d -___ _- -__--_
__- - -
a
Scale.
,
- 60'
C �cj'` IO
�� �\ �±j�` ` � ,�.✓ JL„ <t'- `\—�� �\ ` .+�w`-� .�___� ` v •c�• za�••T.—rtz.yZ:.
/ n`t •� �`. ,� � r .•cam � � .now -�? �`�� -� � -�_—. _ \
.�.• �'�.... } .----•ts-� f-
a \� •���""' '.�-. \ ..: .�•; �i —_ram\
W r'}. �• ,.:.\ ,� 1 \w.J.�/-m,.i'� lC \ \'. �• "cam \ 1 j`•'•/`\�
=LOT 1 �_> `; ' ~ . ' �� LLOT
LANDSLIDE HAZARDS
3A Slumps in materials that have not previously failed
3B Shallow landslides in oversteepened slopes that have not previously faile
2C Avalanches of encroaching landslide material
4A Renewed movements of old slump material
4B Shallow landslides in previously -failed material
The trailing digits indicate the estimated combined probability
of occurrence, in percent, during 25-year periods
Site Survey by Group Four. Inc Job No 88-8020
LOT 4
30
NoTERRA ANDERSON
ASSOCIATES MEADOWDALE B
ceotechnical Consultants Proj- No.840-1 Date3.
fA
cr tri
-4 (n
CD CD (b
TO CA W
0
tv
0 its
cr
%S16.
10
N. MEADOWDALF- RD.
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ITS
VI I
W.
tv
rA
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LA 4=)
10, it
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fi',� ,�I � i � I11 ;,�•• m � rs` , I I � III II',1"rll,l�ll, ,;r;.-;�',.r.,
,71
'� 1' I' `, ,•�� 1.\,�li Is I`I { I' / W.,• l I ��i�.��rr I _t• _` 1 �, I I ( •,dq I to
of
il! it, of
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>
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Ilk,
Kit
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z M
> 0
fill,
0
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Fn .0
xV/
(D CD 0
m
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0-0 r
0—
SOIL CLASSIFICATION gY.TFM
LETTER
MAJOR DIVISIONS SYMBOL
GRAPH•
SYMBOL TYPICAL DESCRIPTIO
GRAVELS
Clean
GW
:..:o
Well -graded gravels, gravel -sand mixtures,
cA
Gravels
�.'' :
little or no fines.
J
6 .0
More than 509'% of
(less than
GP
Poorly -graded gravels, gravel -sand mixtures.
to m
coarse fraction
5% fines).
little or no fines.
Gravelsnon-plastic
4XIAGC
Silty gravels, gravel -sand -silt mixtures.
fines.
Wb N
is larger than
z CD "
a�Clayey
No. 4 sieve.
with fines.
gravels, gravel -sand -clay mixtures.
Q E e
plastic fines.
C� o oo
SANDS
Clean
Well -graded sands, gravelly sands,
Un
Sandslittle
or no fines.
W m �'
than 50% of
(less than
SP
Poorly -graded sands or gravelly sands,
ZMore
5°/% tines).
-
little or no fines.
SM
Silty sands, ,sand -silt mixtures,
Q d
coarse fraction
U0 CO
is smaller than
ands
non -plastic fines.
Sc
Clayey sands, sand -clay mixtures,
No. 4 sieve.
with fines.
plastic fines.
SILTS AND CLAYS
ML
Inorganic silts and very fine sands, rock flour,
silt or claye fine sands or clayey silts with
O
� o
Liquid limit is less than 50%.
CL
—
I �aveal y s of to plasticity,
yclays,y clays, silty clays, lean
ca o
EN
l
OI-
�
��i��1i"
���"i"i'i'i:
Organic silts and organic clays of low
W d
z o z
plasticity.
Q c
SILTS AND CLAYS
MH
Inorganic silts, micaceous or diatomaceous
'sandy
0: N
fine or silty soils, elastic..
u, >
Liquid limit is greater than 50%�
CH
Inorganic clays of high plasticity; fat clays.
W
e yLL
OH
i
1 1
Organic clays of medium to high plasticety,
b�ganic silts.
HIGHLY ORGANIC SOILS
PT
Peat and other highly *organic soils.
DEFINITION' OF TERMS AND SYMBOLS
2" OUTER DIAMETER
SPLIT SPOON SAMPLER
C
TORVANE READING,-tsf
2.4" INNER DIAMETER RING SAMPLER
OR SHELBY
TUBE SAMPLER
qU
PENETROMETER READING, tsf
P
SAMPLER PUSHED
W
MOISTURE, percent of dry weight
�C
SAMPLE NOT RECOVERED
PCf
DRY DENSITY, pounds per cubic foot
Q.
WATER LEVEL (DATE)
LL
LIQUID LIMIT,percent
WATER OBSERVATION WELL
PI,
PLASTIC INDEX
N
STANDARD PENETRATION, blows per foot
__>;T 1TERRA
ASSOCIATES
Geotechnical Consultants
LEGEND FOR BORING & TEST PIT LOGS
ANDERSON PROPERTY
MEADOWDALE BEACH EDMONDS
Proj. No. 840-1 I Date 3/89 I Figure 7
BORING NO.
I
Logged
By CRL
Date 2/14/89
ELEV.
1421
Graph
us
CS
Soil Description
Depth
n )h
Sample
BlNows
N
qu. tsf
Ft.
Ivy ground cover, 18" duff & topsoil
SSp
Grey fine SAND, some silt
5
=
8
4
sm
Grey silty fine to medium SAND.with
10
=
11
15
silt zones, some orange stain
Same, less silt
'15
=
3
22
ml
Grey non -plastic SILT
20
T
14
35
3/15/89 -��-
.1..
sm
Grey silty fine SAND
25
I
8
32
ml
Grey clayey SILT with thin sand lenses.
30
I
21
33
2.0 to
4.5+
ml/
Mixed grey SILT & silty fine SAND
35
9
29
Same
40
I
24
25
mcl
Grey clayey SILT
45
=
10
33
2.5 to 3.5
Boring terminated at depth .50 feet
Ground water observation well installed
BORING LOG
TERRA
ANDERSON PROPERTY
�... - ASSOCIATES
MEADOWDALE BEACH
EDMONDS
-
Proj. No. 840-1
Date 3/89
Figure 8
Geotechnical Consultants
BORING NO, 2
Logged By CRL
Date _ 2/16/89 ELEV. 120±
Graph
CS
Soil Description
De
Sample
Blows
W)
qu tsf
Ft.
Concrete slab
ml/
Grey silty fine SAND and clayey SILT,
=
4
26
sm
some orange stain
5
Grey silty fine SAND with clay
5
33
10
3/15/89 xy
Same, with some organics
-
I
5
24
n
15
Same, with hard clay chunks & wood
Z
13
46
20
sm
Grey silty fine to medium SAND
=
10
19
25
No recovery
_
21
30
ml
Grey sandy SILT
=
12
31
35
Grey SILT
=
22
31
40
mcl
Grey clayey SILT with sandy zones
=
17
37
2.5
45
Same
I
31
24
3.5
50
ch
Grey CLAY
=
24
38
3.5
55
Same
_
25
36
2.5
60
r
Grey CLAY, thin bedding
=
35
35
.4.5
65
CH
Same LL=75; PI=4
=
95/9"
23
4.5+
BORING LOG
TERRA
ANDERSON (PROPERTY
ASSOCIATES
MEADOWDALE BEACH EDMONDS
Proj. No. 84.0-1 1
Date 3/89
Figure 9
Geotechnical Consultants
Logged By CRL
Date 2/14/89
Depth
(ft.) USCS
0
5
10
15
20
TEST PIT NO. I
Soil Description
Elev. 141±
W
N
12" duff and topsoil
39
sm
Brown silty fine SAND, loose, moist
16
Same, grading tan to grey, medium dense, dry
7
Brown silty fine to medium SAND
ml
Brown SILT
25'
sm
Brown silty medium SAND, some gravel,
chunks of hard clay, med dense
Same, marbled gray -brown -orange
20
Test pit completed at depth 18z feet
No ground water observed
<.�. TERRA
.. ASSOCIATES
Geotechnical Consultants
TEST PIT LOGS
ANDERSON PROPERTY
MEADOWDALE BEACH EDMONDS
Proj. No. 840-1 1 Date 1/89 1 Figure 10
Logged By CRL
Date 2/14/89
Depth
(ft.) USCS
0
5
10
15
20
TEST PIT NO. 2
Soil Description
Elev. 1471
W
N
cl
9" duff and topsoil
Mixed brown and grey sand, silt and clay
Grades to CLAY chunks, soft to hard, with
numerous logs
38
sm
Grades to gray silty SAND with organics
33
Test pit completed at depth 14 feet
Ground water seepage at depth 4 feet and below
Sidewalls collapsed
TERRA
ASSOCIATES
. Geotechnical Consultants
0
TEST PIT LOGS-
ANDERSON PROPERTY
MEADOWDALE BEACH EDMONDS
Proj. No. ;;:, Date 3✓89. Figure 11
Logged By CRL
Date 2/15/89
Depth
(ft.) USCS
0
5
10
15
20
TEST PIT NO. 3
Soil Description
Elev. 1391
W
(°/0)
12" duff and topsoil
sm
Brown silty fine SAND
21
ml
Grey brown non -plastic SILT
26
Tan clayey SILT, chunks of hard clay
41
Qu=2.0
to 4.0
sm
Brown silty fine to medium SAND
15
cl
Grey CLAY
34
qu=4.Otsf
Test pit completed at depth 19 feet
No -round water observed
TERRA
ASSOCIATES
Geotechnical Consultants
TEST PIT LOGS
ANDERSON PROPERTY
MEADOWDALE BEACH EDMONDS
Proj. No. 840-1 I Date 3/89 1 Figure 12
Logged By CRL
Date 2/15/89
Depth
(ft.) USCS
0
5
10
15
20
TEST PIT NO. 4
Soil Description
Elev. 153±
W
(a/0)
18" duff and topsoil
43
Grey silty fine SAND with numerous
sm
trees, loose
33
Test pit completed at depth 12 feet
Ground water seepage at depth 3 feet and below
Sidewalls collapsed
TERRA
.. ,- ASSOCIATES
Geotechnical Consultants
TEST PIT LOGS
ANDERSON PROPERTY
MEADOWDALE BEACH EDMONDS
Proj. No. 840-1 1 Date 3/89 1 Figure 13
Logged By CRL
Date 2/15/89
Depth
(ft.) USCS
0--
5
10
15
20
TEST PIT NO. 5
Soil Description
Elev. 137±
W
N
12" duff and topsoil
27
sm
Grey silty SAND with orange stain, wet. loose
27
Test pit completed at depth 12 feet
Heavy ground water seepage in upper:2 feet
:., TERRA
ASSOCIATES
Geotechnical Consultants
TEST PIT LOGS
ANDERSON PROPERTY
MEADOWDALE BEACH EDMONDS
Proj. No. 840-1 Date 3/89 Figure 14
Logged By CRL
Date 2/15/89
Depth
(ft.) USCS .
0
5
10
15
20
TEST PIT NO. 6
Elev. -142±
W
Soil Description (%)
12" topsoil
35
sm
Grey silty fine SAND with zones of soft
clay and chunks of hard clay, loose
i
33
Test pit completed at depth 15 feet
Moderate ground water seepage below depth 6 feet
TEST PIT LOGS
TERRA ANDERSON PROPERTY
ASSOCIATES MEADOWDALE BEACH EDMONDS
Geotechnical Consultants Proj. No. i340-1 I Date 3/8977 Figure 15
3
�rra
I �
North Edmonds
Earth -Subsidence and
Landslide Hazard
n � I
�i
Areas Map j
Legend r
North Edmonds Earth Subsidence and o
Landslide Hazard Area
(See ECDC 23.80.020 B.1 and ECDC 19.10)
(Note: Boundaries are the approximate extent
of previous landsliding; hazards are present(
adjacent to the landslide boundaries)
m!!_1W
Steep Slope Areas:
0 Slope of 40% or steeper and
with a vertical relief of ten (10) ft or more
(See ECDC 23.80.020 B.2) p� z t,
(
Minimum buffer equal to the height
of the steep slope or• 50 feet, whichever
is greater (see ECDC 23.80.070 A.1) r' r %VA
(The buffer shown is the minimum buffer !,r J .i
L adjacent to the North Edmonds Subsidence
and Landslide Hazard Area; a similar (I`
jlrr5\
buffer would apply to steep slope areas,;`1
but is not shown on this map for clarity) t�� ' (:
i
y4 , / "e
2 ft Topographic Contour
Vertical datum: NAVD88 ` "XI" �7
Parcel ''
n
0 100 Z' I F�
11 ff(<<l� j'7 off'
00 i ' , J !� �
ScWe In Feet
•1 I !, it%:IJ�� a i' •'�f'/x ,"^'>ti1!;r+!
J I �S�ur• ,� •, rcw
c
Map created by Landau Associates, Inc. (May 2006)
Aerial photo: City of Edmonds
Topographic contours and steep slopes data derivedzm,
from UDAR data: City of Edmonds (February 27. 2005) �,r!f ,ri,r,li l =}
,liy,,tiul:
r �r
4,
/��jfja6��`?J ��'7 �`s•Fi•' ti'� jit (F"� '�/ ', f r/ ,((//y-� J„ � � i 4
f{� J'' JITJ�.ii fir jluJ p ! F c� . _
yam. `.L�`"1~ ` � J s-• / 1 .
i J �J (J �I-`�Kj�'111'1
c v � `� �i\� a�. L f �rr�-�
r i) , i 1, i; 1`6,s it
C
3 v
1I� II'i
, I 05RU
L J E2E)O
��'1V-•, r �' i 1 �:��ia: � i I j t I i{; J li l`,JIi�J�Ii, C, I� :'l5 '•`��4i
' 7•`' j ,]
1 JulP�'l�';'t �i,1�.-.'i� �# l�t'y`'•'Js'ii l�(!r
it
Pursuant to Edmonds (ommunity Development Code Chapter 19.10 sites designated within or near the North Edmonds
Earth Subsidence and Landslide Hazard Area shall be designated on this map which indicates areas of earth subsidence and
landslide hazards in excess of normal allowances.
In order to designate the 'subject project development site located at ilk It -7 �4 �L \&T— Edmonds,
Washington, the following maps, surveys or other noted items below were used:
• Geotechnical Rep%rt Prepared by Z ZA tlr�?�4Go �1
• Land Survey Prelared by KOPCFOT GuY 6120EN e-
"I certify under penalty of perjury that the site location designation has been made to the best of my knowledge and belief,
following an investigatioli of all information and documentation'in my possession as well as reasonably obtainable information
in the possession of othea•s, including public agencies. Any information which would tend to designate a differing location for
the site is attached as a part of my designation as well as all information upon which I reasonably relied."
Site Plotted by krZk5 -TIP ► A-1J 5 01J Date 3 ' 27 ' �8
Signed V�/1�� V ` r` w�ti r Date
Title
V
APR - 3 2008
BUILDING DEPT.
r
F
0 20
i
Scale 1 = 0' f
E
2 2 TEMP RLTERFENCE
IOo
F
It
CLEAN EX. CB OF ALL 3 F' TEMP
SEDIMENT PRIOR TO F SEDIMENT
START OF CONSTRUCTION . — TRAP
c
t
4 TEMP GRAVEL F l ... Q,
_ WRYF
F.
2 TEMP FlLTER
F r
/ �21 6
a :�•,�� ;
t?}d,, .... ....:.�
,
1'ii1 >r ii 3 E s !
CLEAN EX. CB OF ALL 3 ,TEMP
SEDIMENT PRIOR TO F /
START OF CONSTRUCTION 77 TRAP
/ l _
f
If
`•i
=r,•,. �/. Z- `V rt '�ii ��:Y ! it r r f f+ r f ' j r
� 1 L �j... r F 1 �• > i F f 3 ; I rr i /
_� � /'•.� ,3 �, � i t i f f � i : i 3 f i I, r >! 1r
"1 r= 1 � Y sw � i ! r� r f t3 i f-, i 3 f r � r•
J5 i
/ , Fir +r+ W s •,"' "?.iS N %3 �' + f i. <� i ,33 +• ,`. f r � f � �-
�+ � i^ � s w O rr tD {��l ��a'• J`r j r f r i '
;q ; a V 3t 1 f f 7 f `A7 dN 7
TOP—
............................
6
Top-10, ,�' ; �� : i=.:��?�zi:: R\ PN 1A
70E—) �b3 t r L �O P C' Q
Ci i et: 1 � 1 O`. � �O'( CJ F-i: •
a.. V
F
Q-
D , t ROCKERY 1 OR MODULAR rJ L
BLOCK WALL_
' wi.iai'- Yii;tl
'
0 ;§DEBAR CAiP ire ij 3' rs. W J.u? i! FROM (''8,RN 'R
..,'.* TRACT A (COMMON AREA)
THIS VICINITY MAP, BASED ON THE GEO-TECHNICAL REPORT BY
ZZA—TERRACON . THERE ARE NO LANDSLIDES, DEBRIS FLOWS OR
MUD FLOWS WITHIN 100 FEET OF THE PROPERTY LINES.
77
APR. — 3 �iCr��
r
BUILDING [KEPT.
2
STREET FILE
SURVEY DESCRIPTION:
/
/ 3
17///
M
r / j RIM 86.65
IE 77.15
r � 3
r-
EASEMENT HOUSE N /� r x 129.9
#16121
Vol
30'
;ram 4z� I t tx92.6//
Q a i11 / r II 1 I II I Ota
r / BOA08 I / / // 90.8"11 N 73 Op 43� � / � I Ir I G-t A 100I 1 1 I I
--- I I
RIM 85.21 / 92% 2 00' R1d6 6� I I I I 1
RIM 79.34 1 /^ / I I
r 80 1 / / Y / / o / 5005 S�Q. FT
� r/ / / 0.1 X ACAEs
HEDGE I 11 l/ /I 11�58 I CL
N II I
r
�� RIM 90.68/ � / / / / FND REBAR & CAP N 1.51' & W 1.0' FROM CORNER
I
� r / /I l l� I I GRASS / C Illp.91 1 I
81.29 r / / l l rl l I / / 1 `y,, h11v7A
/RIM 102.9 I 4r 1 -:� I
O`
I
ir"o�, I , 9- 4.3 £
2.26 I / I I I l l I ► I 35,
CONC 108.2
/ 1 r
2ND FL TOP RAILING 120.0 --
-I ;
r RIM 82.10 co ;� HOUSEqG5-1L6
/ I 1
r / // 92.2 S sss', S8. / o / 1 ?� #16121 `- Ci - �p't 6 w
RIM 83.91 1 I'
ROCVj 4 �F I I r iN i rn
83.74 a /
/ 2 1 0 /" \ / IFND REBAR & CAP N 0.73' & W 0.95' FROM CORNER L r't
1 rn /5 \
83.63 1 1 1 `�- SET\RE R& CAP Z
(PLANTER \ '
ASPH. i I 1 � ► N 85'30135" yy - -
/
PVMT � I � 1 ASPH1
104.68
N NO PIPES 86.50 RIM 84.30 RIM PIP9.1 ES
RIM 99.74 - - - - _ _
162ND ST SW IE 12" 97.35
GRAPHIC SCALE
LOT 9 LORIAN WOODS ACCORDING TO THE PLAT THEREOF RECORDED IN VOLUME
51 OF PLATS, PAGES 145-146, RECORDS OF SNOHOMISH COUNTY, WASHINGTON.
SUBJECT TO AND TOGETHER WITH ALL EASEMENTS, RESTRICTIONS, RESERVATIONS,
AND RIGHTS OF RECORD IF ANY.
SITUATE IN THE COUNTY OF SNOHOMISH, STATE OF WASHINGTON.
EQUIPMENT AND PROCEDURES
ALL MEASUREMENTS WERE MADE WITH AN ELECTRONIC THEODOLITE WITH A ONE
SECOND HORIZONTAL AND VERTICAL DISPLAY AND MANUFACTURES STANDARD
POINTING DEVIATION OF THREE SECONDS AND AN ELECTRONIC DISTANCE
MEASUREMENT DEVICE WITH A STANDARD DEVIATION OF 3MMf 3PPM
FIELD TRAVERSE METHOD IN COMPLIANCE WITH W.A.C. 332-130-090
ALL POINTS INDICATED FOUND WERE VISITED IN 6-2006 UNLESS OTHERWISE
NOTED.
LEGEND
•
FOUND 5/8"" X 24" REBAR WITH CAP OR AS NOTED
x
SET 60D NAIL OR AS NOTED
&
MONUMENT IN CASE
GAS VALVE
®
STORM STUB?
MONITOR WELL
1E
WATER METER
-o-
UTILITY POLE
CALC
CALCULATED
DW
DRIVE WAY
FL
FLOW LINE
G
GAS
IE
INVERT ELEVATION
S
SEWER
SD
STORM DRAIN
W
WATER
DECIDUOUS OR ORNAMENTAL EVERGREEN TREE
TRUE EXTENT OF CANOPY NOT SHOWN
X CONIFEROUS TREE
TRUE EXTENT OF CANOPY NOT SHOWN
O / RIM 85.04 200.0 SPOT ELEVATION IS LOCATED AT THE DECIMAL POINT OF
N IE 75.14 �- ELEVATION (200.0) UNLESS AS NOTED WITH LEADER OR X
LAND SURVEYORS CERTIFICATE
THIS MAP CORRE
DIRECTION IN C01
ACT AT THE REQ
2953�1
/�L
REPRESENTS A SURVEY MADE BY ME OR UNDER MY
MAN TH T E REQUIREMENTS OF THE SURVEY RECORDING
nOF EEVI ENjq JOHNSON IN JULY, 2006
CERTIFICATE NO. 29539
REVISIONS
9/18/06 CORRECTED
PROP. DIMENSION
¢' `11G i' 6 S • 1
GENERAL NOTES
HORIZONTAL DATUM: PLAT
VERTICAL DATUM: SEA LEVEL OF
0.00 (ASSUMED) 6:07PM 7/17/06
SURVEYED BY
RGG
DRAWN BY
CHECKED BY
APPROVED BY
DATE PRINTED
1 8/08/0,
SCALE
1" = 20'
F.B. NO.
10 PG 34
( IN FEET )
1 INCH = 20 FT.
AUDITORS CERTIFICATE
FILED FOR RECORD THIS DAY OF
M. UNDER AUDITORS FILE NUMBER
THE REQUEST OF R.G.GREENE
COUNTY AUDITOR BY DEPUTY AUDITOR
,2006 AT
JOB NO.
GREENE LAND SURVEYING PLAT OF SURVEY 2006.26
FOR DRAWING NO.
EDONDS, WASHINGTON STEPHEN C JOHNSON 6-26
7906 199TH ST SW SHEET OF
PHONE (425) 697-6606 FAX (425) 697-6604 PTN: S.W. 1/4 S.W. 1/4, SEC. 5, T 27 N, R 4 E, W.M. 1 1
ZZA Zipper Zeman Associates Inc.
'' Geotechnical and Environmental Consulting
' A lrerracon Company
M Y
' Mr. Steve Johnson
745 Laurel Street
' Edmonds, Washington 98020
Subject: Report of Geotechnical Services
' Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
Edmonds, Washington
' Dear Mr. Johnson:
81052440
May 30, 2008
RECEIVED
J U L - 1 2008
BUILDING DEPT.
' Zipper Zeman Associates, Inc. (ZZA) is pleased to present herein a copy of the above -
referenced report. This report presents the results of our surface and subsurface exploration and
geotechnical engineering study relative to foundation and construction considerations for the
' referenced project. Our services were completed in. accordance with our Proposal for
Geotechnical Services (J-2440) dated April 5, 2006 and Supplements to Agreement for Services
dated February 9, 2007 and May 28, 2008.
' The purpose of the study was to establish general surface and subsurface conditions at the
site from which conclusions and recommendations regarding foundation design and construction
' considerations could be formulated. The scope of our services consisted of a literature review,
surficial reconnaissance, subsurface exploration, geotechnical engineering analysis, and
preparation of this report.
At the time this report was prepared, project plans were in the preliminary stage. As
such, we recommend that ZZA be allowed the opportunity to review the plans and specifications
' for the project once they become available to determine that the recommendations presented
herein have been properly interpreted with respect to this project. This report is an instrument of
service and the conclusions presented herein are in respect to the subject property and have been
' prepared in accordance with generally accepted geotechnical engineering practices. This report
has been prepared for the exclusive use of Mr. Steve Johnson, and other members of the project
team, for specific application to this project and the stated purpose.
SITE AND PROJECT DESCRIPTION
' The subject property is located near the northeast corner of the intersection of 741h Place
West and 162" Street SW in Edmonds, Washington. The roughly rectangular shaped parcel is
' approximately 5,005 square feet in size and is located within a moderately steep to steep west -
facing slope. The parcel is bounded to the west by 74th Place West and to the north, east, and
south by single-family residential development. Existing single-family structures are located
' about 18 feet north and 16 feet east of the subject parcel.
"TRT FILE
' 18905 33r1 Avenue West # 1 17, Lynnwood, WA 98036 425-771-3304 Fax: 425-771-3549
' Proposed Single -Family Residence
Z �� Lorian Woods Plat, Lot 9
81052440
May 30, 2008
Page 2
' Preliminary plans indicate that the residence will encompass the majority of the parcel.
We understand that "common area" associated with the Lorian Woods Plat is located along the
' west, east, and south sides of the subject parcel, and that Lot 10 is located immediately adjacent
to the northern lot line of the subject parcel. The plans indicate that the house will consist of
' three floor levels stepped into the slope. The majority of the lower level has a finished floor
elevation of 82.2 feet. A 14 foot by 15 foot "Virtual Golf' area is shown near the northwest
corner of the lower level with a finished floor elevation of 80.7 feet. The plans indicate middle
and upper level finished floor elevations of approximately 92 feet and 101.5 feet, respectively.
' We understand that the residence will be supported on conventional shallow spread foundations
with subsurface concrete walls. A combination of slab -on -grade concrete floors and wood
' framed floors over crawl spaces is planned. We understand that the residence will be accessed
by a lower level driveway and an upper level parking area. We understand that the driveway and
parking areas will incorporate cast -in -place concrete retaining walls up to about 5 feet high. The
' proposed building layout and existing site features are shown on the enclosed Site and
Exploration Plan, Figure 1.
The site is located within an area designated as the North Edmonds Earth Subsidence
Landslide Hazard Area (North Edmonds ESLHA). Portions of the North Edmonds ESLHA have
reportedly experienced historic slope instability. The North Edmonds ESLHA and the subject
site meet the criteria established for Earth Subsidence and Landslide Hazard Areas presented in
Chapter 19.10 of the City of Edmonds Building Code. As such, permitting and development of
the site must meet the guidelines presented in Chapters 19.10 and 23.80 of the Edmonds
' Community Development Code (ECDC).
REGIONAL GEOLOGY
' We assessed the regional geology of the site and the surrounding vicinity by reviewing
the following regional publications and geotechnical reports.
' • Washington Department of Natural Resources; Preliminary Surficial Geologic Map of
the Edmonds East and Edmonds West Quadrangles, Snohomish and King Counties,
' Washington; Map GM-14, 1975.
• Roger Lowe Associates, Inc.; Final Report, Landslide Hazard Investigation,
Meadowdale Area, Edmonds, Washington; October 16, 1979.
' • GeoEngineers Inc.; Report of Geotechnical Consultation, Property Value Appraisal and
Assessment, Meadowdale Landslide Area, Edmonds, Washington; February 28, 1985.
• Landau Associates; North Edmonds Earth Subsidence and Landslide Hazard Area
Summary Report, Edmonds, Washington; March 14, 2007.
The project site is located on the western margin of the Intercity Plateau within the Puget
' Lowland. The Puget Lowland is a north -south trending depression bounded on the east and west
by the Cascade and Olympic mountain ranges, respectively. The topography and geology of the
Puget Lowland and the Intercity Plateau are a direct result of several cycles of regional glaciation
during the Pleistocene epoch. The most recent cycle of glaciation, known as the Vashon Stade of
the Fraser Glaciation, ended approximately 13,500 years ago. The Vashon Stade is believed to
1
81052440 Johnson Res Report 053008.doc
' Proposed Single -Family Residence
ZZA Lorian Woods Plat, Lot 9
' 81052440
' May 30, 2008
Page 3
' have covered the Puget Lowland with up to 3,000 to 5,000 feet of glacial ice in the deeper
portion of the Lowland.
' The PreliminarySur icial Geologic Ma o the Edmonds East and Edmonds West
.f g P .f
Quadrangles, Snohomish and King Counties, Washington describes the site and surrounding
' vicinity as being mantled by Quaternary age "Old Landslide" deposits.. The Old Landslide
deposits are described as large slumps that occurred during the ablation (retreat) of the Puget
Lobe of the Vashon ice sheet by lowering of water table levels. The publication indicates that
the landslides may have been active since original movement. This large landslide is locally
referred to as the Meadowdale Landslide Hazard Area and the Meadowdale Landslide Complex,
and is currently designated as the North Edmonds Earth Subsidence and Landslide Hazard Area
by the City of Edmonds. The geologic units mapped around the landslide suggest that the
landslide occurred primarily within Whidbey Formation deposits and may include deposits of the
underlying Double Bluff Drift.
The Whidbey Formation comprises pre-Vashon interglacial fluvial sediments. The
' formation consists primarily of bedded sand, silt, and clay. Sorting is generally good within each
individual bed. The upper portion of the unit is typically oxidized. Tectonically contorted
bedding is not uncommon. Due to clay beds within the Whidbey Formation, groundwater
percolating down through sandy zones tends to build up and move laterally on top of the clay
beds. Where these beds daylight on hillsides and coastal bluffs, groundwater seepage and
landsliding are not uncommon.
' The Double Bluff Drift comprises pre-Vashon glacial and non glacial deposits. The unit
contains fluvial gravels with variable silt and sand content, lodgment till, pebbly fine grained
' glacial lacustrine silts, and massive deposits of silt and clay. The unit may show tectonic
deformation. The unit has a low permeability and hydraulic conductivity, and perched
groundwater often develops in the overlying Whidbey Formation deposits, forming a weakened
zone in which the Whidbey Formation soils can slide.
The 1979 Roger Lowe Associates report indicates that the site is located within the
' Meadowdale Landslide Hazard Area. The report describes the landslide mass as extending about
3,200 feet in a north -south direction along the shoreline of Puget Sound and up to 650 feet in an
easterly direction from the Burlington Northern railroad right-of-way which is located near the
' toe of the landslide area. The topographic relief of the landslide area is about 150 feet, while the
headscarp of the landslide extends up to about elevation 300 feet. The landslide mass is reported
to be on the order of 20 to 50 feet thick. The initial movement of the landslide is believed to
' have occurred about 7,000 years ago as a result of rising sea levels associated with glacial retreat
and shoreline erosion. Historic movement of the landslide complex has primarily occurred
within a zone approximately 400 feet wide adjacent to and east of the Burlington Northern
' railroad right-of-way from the 1940's through the 1770's.
The evaluation completed by Roger Lowe Associates included a -landslide hazard risk
assessment and the development of a Landslide Hazard Map for the Meadowdale Landslide
Complex and surrounding vicinity. The 1979 Landslide Hazard Map suggests that the western
81052440 Johnson Res Report 053008.doc
A
Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
81052440
May 30, 2008
Page 4
portion of the site is located within a 4A90 hazard area. This designation indicates a 90 percent
probability of movement within an existing slump during a 25 year period. The eastern portion
of the site appears to be located within a 4A35 hazard area, indicates a 35 percent probability of
movement within an existing slump during a 25 year period. In the early 1980's, the City of
Edmonds implemented measures that contributed to. lowering of groundwater levels within
portions of the Meadowdale landslide area. GeoEngineers reevaluated landslide hazards within
the Meadowdale Landslide Complex to account for decreased groundwater levels and developed
a revised Landslide Hazard Map. The revised hazard map indicates that the western and eastern
portions of the site have a 30 percent and 10 percent probability of movement within an existing
slump during a 25 year period, respectively.
The 2007 report prepared by Landau Associates provides a summary of the information
presented in the referenced Roger Lowe and GeoEngineers reports, and an earlier 1968 report
prepared by Dames and Moore. The 1968 Dames and Moore report was not available for our
review at the City at the time this report was prepared. The Landau Associates report also
discusses typical landslide mechanisms and recommended geotechnical report requirements for
different zones within the North Edmonds ESLHA.
CITY OF EDMONDS LITERATURE REVIEW
In addition to our review of the reference Roger Lowe Associates, GeoEngineers, and
Landau Associates reports completed for the City of Edmonds, we completed a review of
documents on file with the City of Edmonds relative to landsliding, ground subsidence, erosion,
and other geotechnical related problems within an approximate 400 foot radius of the subject
site. Specifically, our review included the following documents.
1. Associated Earth Sciences, Inc.; Limited Slope Reconnaissance, 16202 — 72"d Avenue
West, Edmonds, Washington; March 15, 2001.
2. City of Edmonds; RE: Slope Investigation, Johnson Residence, 16121 — 74`" Place West,
Edmonds, Washington; March 23, 2001.
3. Landau Associates; Slope Stability Consultation, 16202 — 72"d Avenue West, Edmonds,
Washington; April 19, 2001.
4. City of Edmonds; RE: Slope Stability Consultation, 16202 — 72"d Avenue West, Edmonds,
Washington; April 26, 2001.
5. Landau Associates; Landslide Evaluation Meadowdale .Area — Lorian Woods/Sequoia
Ridge Plats, Edmonds, Washington; September 25 2003.
6. City of Edmonds; RE: Localized landslide near Lorian Woods/Sequoia Ridge Plats,
Edmonds, Edmonds, Washington; September 25, 2003.
7. Terra Associates, Inc.; Geotechnical Consultation, Deck Repair, Johnson Residence,
Lorian Woods, Lot 8, Edmonds, Washington; February 27, 2003.
8. Terra Associates, Inc.; Final Letter, Earthwork Observation and Testing, Johnson
Residence, Lorian Woods, Lot 8, Edmonds, Washington; June 13, 2003.
Documents 1 through 4 are associated with a landslide that occurred on September 13,
1998 and appeared to reactivate in February 2001. The landslide(s) appear to have occurred
81052440 Johnson Res Report 053008.doc
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Page 5
about 350 to 400 feet southeast of the subject property on a steep west -facing slope located west
of 16202 72nd Avenue West. The slope was reported to have an inclination of about 1 H:1 V and
' a total relief of about 120 feet. The slide was reportedly shallow in nature, consisted of a rapidly
moving mud and debris, and extended from the toe to the top of the slope. The risk of future
landsliding adversely affecting the properties immediately above and below the steep slope was
' considered high.
Documents 5 and 6 are associated with a landslide that occurred on or around September
15, 2003. The landslide reportedly occurred about 400 feet northeast of the subject property
between Lot 2 of Lorian Woods and Lot 4 of the Sequoia Ridge Plat. The slide reportedly
I' consisted of a combination block slide and mudflow that extended to a depth of about 3 to 5 feet
(measured perpendicular to the slope face) and occurred on the face of a steep landslide scarp.
Ground cracks were observed up gradient (east of the landslide) and the documents indicate an
increased risk to properties immediately above and below the slide area.
Documents 7 and 8 appear to be associated with settlement damage to a small concrete
patio slab and two patio columns located near the southwest corner of the residence located on
Lot 8 of Lorian Woods, about 15 feet east of the subject site. Settlement damage reportedly
occurred due to consolidation of fill soils. The documents indicate that the slab was removed
and replaced above a compacted subgrade and that the two columns were supported on driven 2-
inch diameter pipe piles.
SITE CONDITIONS
We completed a visual reconnaissance and subsurface exploration of the site in June
2006. Our visual reconnaissance was updated in May 2008. The surface and subsurface
conditions are described below. Pertinent site features and approximate exploration locations for
the proposed development area are shown on the Site and Exploration Plan, Figure 1. Details of
the field exploration procedures along with the exploration logs are presented in Appendix A.
Surface Conditions
The subject parcel consists of a moderately steep to steep west -facing slope with
inclinations ranging from about 28 to 40 percent and a total relief of about 20 feet. A steep west -
facing slope with inclinations ranging from about 45 to 55 percent and a total relief of about 6 to
7 feet is present within the "common area" located between the subject parcel and the 741h Place
West right-of-way. This steeper slope area appears to be the result of cuts associated with
roadway and utility construction.
The parcel is predominantly vegetated with grass and includes some shrubs and
ornamental plantings within the northern portion of the lot. We did not observe any obvious
indications of recent slope movement, such as ground cracks or hummocky topography at the
time of our evaluation. We did not observe any standing or flowing surface water or indications
of groundwater seepage within the proposed development area at the time of our evaluation.
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Proposed Single -Family Residence
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81052440
May 30, 2008
Page 6
The base of a steep west -facing slope is located about 150 to 180 feet east of the subject
parcel near the eastern side of Lot 8. The slope exhibited geomorphic indications of surficial soil
creep and shallow surficial landsliding. Based on our observations and published geologic maps
and geotechnical reports of the area, this steep slope is interpreted as a portion of the
Meadowdale landslide headscarp.
Subsurface Conditions
The subsurface exploration completed for this study consisted of two hollow stem auger
borings within the proposed building footprint. Boring B-1 was advanced near the western side
of the proposed residence and was completed to a depth of approximately 56.5 feet below the
ground surface. Boring B-2 was advanced near the eastern side of the proposed residence and
was completed to a depth of approximately 51.5 feet below the ground surface. The approximate
exploration locations are shown on the Site and Exploration Plan, Figure 1. Figure 2 presents a
generalized subsurface profile depicting conditions down the fall line of the west -facing slope.
In general, the explorations disclosed approximately 36 to 45 feet of colluvial deposits
underlain by undisturbed native soils interpreted as Whidbey Formation deposits. The colluvial
soils generally consisted of loose to medium dense sand with variable silt content and medium
stiff to stiff, silty clay and clayey silt with variable sand content. The fine grained portions of the
colluvium exhibited a disturbed, blocky texture with inclusions of hard silt and portions of the
granular deposits exhibited a lack of depositional structure. The underlying Whidbey deposits
generally consisted of very stiff to hard, moist, massive to finely laminated clayey silt and
extended to the maximum depth explored at 56.5 feet below the ground surface. The subsurface
soils disclosed in our explorations were generally consistent with the published geologic units for
the site vicinity.
Groundwater
Groundwater was observed in borings B-1 and B-2 at the time of our evaluation. The
observed groundwater was interpreted to represent a perched condition above the low
permeability, undisturbed Whidbey Formation deposits encountered below the colluvium.
Monitoring wells were installed in borings B-1 and B-2 to record fluctuations in the groundwater
conditions. Groundwater levels recorded at the time of drilling and during subsequent
monitoring well soundings are presented in the table below.
GROUNDWATER CONDITIONS
Exploration
Number
Date Measured
Groundwater Depth Below
Ground Surface (ft)
Groundwater Elevation (ft)
06/22/2006 *
15.5
75
B-1
1 10/09/2006
1 12.6
77.9
11 /16/2006
1 11.4
79.1
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Proposed Single -Family Residence
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81052440
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06/22/2006 *
13.5
89.5
B-2
10/09/2006
20.3
82.7
11 / 16/2006
19.3
83.7
* Groundwater level estimates developed at the time of drilling.
Groundwater conditions should be expected to fluctuate due to changes in season,
precipitation patterns, site utilization, on -site or off -site irrigation activities, and other on- and
off -site factors.
CONCLUSIONS AND RECOMMENDATIONS
IGeneral
We understand that the residence will consist of three floor levels stepped into the slope.
The majority of the lower level has a finished floor elevation of 82.2 feet. A 14 foot by 15 foof
"Virtual Golf' area is located near the northwest corner of the lower level with a finished floor
elevation of 80.7 feet. The plans indicate middle and upper level finished floor elevations of
approximately 92 feet and 101.5 feet, respectively. We understand that the residence will be
supported on conventional shallow spread foundations with subsurface concrete walls. A
combination of slab -on -grade concrete floors and wood framed floors over crawl spaces is
planned. We understand that the residence will be accessed by a lower level driveway and an
upper level parking area. We understand that the driveway and parking areas will incorporate
cast -in -place concrete retaining walls up to about 5 feet high.
Preliminary plans indicate that the residence will encompass the majority of the parcel.
Based on the subsurface conditions disclosed at the exploration locations, the project appears
geotechnically feasible utilizing conventional shallow foundation support and slab -on -grade
concrete floors or wood framed floors over crawl spaces. However, the site is mapped within a
portion of the North Edmonds ESLHA having a mapped probability of movement of 10 to 30
percent in a 25 year period. Given the lateral extent, depth, and topographic relief of the North
Edmonds ESLHA, it is our opinion that mitigation of this risk of movement is not feasible. Our
analyses also indicate that portions of the site soils are susceptible to liquefaction and settlement
during a design seismic event. Given the proximity of the residence to the property lines, the
planned cut depths, and the recommended maximum temporary cut slope inclination of 1.5H:1 V,
we anticipate that temporary shoring will likely be necessary.
Specific recommendations for project design, including a more detail discussion
regarding the above concerns, are presented in the following sections.
Seismic Considerations
Tectonic Setting
The tectonic setting of western Washington is dominated by the Cascadia Subduction
Zone formed by the Juan de Fuca plate subducting beneath the North American Plate. This
81052440 Johnson Res Report 053008.doc
' Proposed Single -Family Residence
��� Lorian Woods Plat, Lot 9
' 81052440
May 30LNIM, 2008
a Page 8
1 and inte late earthquake sources. Seismic hazards relate to
setting leads to mtraplate, crusta , a rp q
risks of injury to people and damage to property resulting from these three principle earthquake
sources.
Soil Liquefaction
Liquefaction is a phenomenon wherein saturated cohesionless soils build up excess pore
water pressures during earthquake loading. Liquefaction typically occurs in loose soils, but may
occur in denser soils if the ground shaking is sufficiently strong. We assessed the potential for
liquefaction using the simplified procedure originally developed by Seed and Idriss (1971), and
updated by Idriss (2004). It is an empirical method based on surficial expressions of soil
liquefaction during past earthquakes. The method involves a comparison of earthquake -induced
stresses to soil strength at the location and depth of each exploration sample. Soil strength is
correlated to the standard penetration resistance blow count, (N1)60, after it has been normalized
to an effective overburden pressure of 1 ton per square foot and corrected for drilling/sampling
procedures and fines content. Earthquake -induced stresses are estimated with an equation that
includes horizontal Peak Ground Acceleration (PGA) at the ground surface and earthquake
magnitude as variables.
Our analysis was completed for a magnitude 7 design earthquake with a 2,500-year return
period, and used a PGA of 0.33g. This PGA value is based on USGS National Seismic Hazard
Mapping Project 2006 IBC spectral ordinates and has been factored in accordance with the 2006
International Building Code (IBC) seismic design method. The USGS obtained these values by
performing probabilistic seismic hazard analyses that considered all potential earthquake sources
that may contribute to strong ground shaking at the site. Magnitude, distance, and probability of
' occurrence were all factored into this hazard analysis.
Based on our analyses, zones of liquefied soil are anticipated to develop within the
' granular portions of the site colluvial deposits during ground shaking from an event with a 2,500-
year return period. Based on the conditions encountered in borings B-1 and B-2, it appears that
potentially liquefiable zones are laterally and vertically discontinuous due to the disturbed nature
' of the colluvial deposits. Soil liquefaction may be expressed at the ground surface as sand boils,
ground cracks, vertical settlements, and lateral displacements. However, given the discontinuous
nature of the potentially liquefiable zones and the presence of non -liquefiable clayey soils
' located above the perched water table, surficial expression of soil liquefaction such as sand boils
and ground cracking may not be observed at the project site.
Ground shaking from an earthquake can result in subsidence of the ground surface and
settlement of on -grade supported facilities. Seismic induced settlements tend to be greatest in
loose granular soils, and particularly soils which are susceptible to liquefaction. Based on the
results of our analyses, we estimate that total vertical settlements on the order of 1 to 2 inches
could be experienced at the site during a design earthquake. Differential settlement could
approach''/2 to 1 inch over a distance of about 30 feet.
81052440 Johnson Res Report 053008.doe
' Proposed Single -Family Residence
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81052440
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Page 9
International Building Code Seismic Design Parameters
It is our understanding that seismic design for this project will be completed in
accordance with the procedures presented in the 2006 IBC. Per the 2006 IBC seismic design
procedures, the presence of liquefiable soils requires a Site Class definition of F. A Site Class of
' F requires a site -specific dynamic site response analysis, except for structures with periods of
vibration equal to or less than 0.5 seconds. For structures with periods of vibration equal to or
less than 0.5 seconds, site coefficients Fa and F„ may be taken equal to the values for the Site
' Class determined without regard to liquefaction. The structure is expected to have a period less
than 0.5 seconds. Based on the subsurface conditions encountered at the site and published
geologic literature, it is our opinion that an IBC Site Class of D describes the average properties
of soil beneath the site to a depth of 100 feet, when disregarding liquefaction. This designation
describes soils that are considered stiff with a shear wave velocity between 600 and 1,200 feet
per second, average Standard Penetration Test values between 15 and 50, and an undrained shear
strength between 1,000 and 2,000 psf.
The USGS National Seismic Hazard Mapping Project computes the 2006 IBC spectral
ordinates (5 percent damping) at building periods of 0.2 and 1.0 seconds for ground motions at
the project site with a 2 percent probability of exceedance in 50 years (2,500-year return period)
' as 1.23g and 0.43g. Therefore, we recommend that Ss and S1 be assigned values of 1.23g and
0.43g, respectively.
Geologic Hazard Area Considerations
General
Chapter 23.80 of the ECDC regulates development in Geologically Hazardous Areas.
Geologically Hazardous Areas include Erosion Hazard Areas, Landslide Hazard Areas, and
Seismic Hazard Areas. A summary of our evaluation regarding these geologic hazards is
presented below.
Erosion Hazard Areas
In general, the site consists of a moderately steep to steep west -facing slope with
inclinations ranging from about 28 to 40 percent and a total relief of about 20 feet. A steep west -
facing slope with inclinations ranging from about 45 to 55 percent and a total relief of about 6 to
7 feet is present .within the "common area" located between the site and the 741h Place West
right-of-way. This steeper slope area appears to be the result of cuts associated with roadway
and utility construction. The 1983 Soil Survey of Snohomish County Area, Washington prepared
by the USDA Soil Conservation Service maps the site as being mantled by Alderwood gravelly
sandy loam (15 to 25 percent slopes). Based on the site slope inclinations and the mapped
USDA soil type, it appears that the site meets the criteria for Erosion Hazard Areas as
established in Section 23.80.020 of the ECDC.
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Based on our observations, it is our opinion that the planned development is
geotechnically feasible provided that an erosion and sediment control plan is developed that
minimizes erosion from disturbed areas with preventative measures. Chapter 23.80 of the ECDC
indicates that an erosion and sediment control plan should be developed in accordance with
Chapter 18.30 of the ECDC. Preventative temporary erosion control measures may include, but
are not limited to, silt fences, straw waddles, gravel check dams, sedimentation ponds, plastic
sheeting on temporary construction slopes during wet weather, or other measures approved by
the City.
We recommend that permanent vegetation be established as soon as feasible and within
one growing season. Permanent revegetation may include the use of hydroseed. Revegetation of
permanent slopes steeper than 3H:1 V may be enhanced through the use of rolled erosion control
and root reinforcement materials such as Jute matting or Curlex II.
Landslide Hazard Areas
The site is located within a documented landslide area designated as the North Edmonds
ESLHA by the City of Edmonds. The extent and nature of this landslide area are described in
the Final Report, Landslide Hazard Investigation, Meadowdale Area, Edmonds, Washington
prepared by Roger Lowe Associates, 1979, the Report of Geotechnical Consultation, Property
Value Appraisal and Assessment, Meadowdale Landslide Area, Edmonds, Washington, prepared
by GeoEngineers, 1985, and the North Edmonds Earth Subsidence and Landslide Hazard Area
Summary Report, Edmonds, Washington, prepared by Landau Associates, 2007.
The evaluation completed by Roger Lowe Associates included a landslide hazard risk
' assessment and the development of a Landslide Hazard Map for the Meadowdale Landslide
Hazard Area and surrounding vicinity. In the early 1980's, the City of Edmonds implemented
measures that contributed to lowering of groundwater levels within portions of the Meadowdale
' landslide area. GeoEngineers reevaluated landslide hazards within the Meadowdale Landslide
Complex to account for decreased groundwater levels and developed a revised Landslide Hazard
Map. The revised hazard map indicates that the western and eastern portions of the subject site
have a 30 percent and 10 percent probability of movement within an existing laterally extensive
' . slump during a 25 year period, respectively.
' The 2006 North Edmonds ESLHA Map prepared by Landau Associates for the City of
Edmonds places the site within a mid slope bench of the landslide mass. The 2007 Landau
Associates summary report divides the North Edmonds ESLHA into Zones A though E based
' primarily on geology, topography, and anticipated landslide mechanisms. Based on our
reconnaissance of the site and the surrounding vicinity, and our site specific subsurface
explorations, it is our opinion that the subject site is located within Zone B.
' Due to the site location within the North Edmonds ESLHA and the site specific
geotechnical and topographic conditions, the site appears to meet the criteria for an Earth
Subsidence and Landslide Hazard Area based on Chapters 19.10 and 23.80 of the ECDC. This
designation generally applies when a site is located within mapped areas of historic landsliding
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or areas with slope inclinations greater than 15 percent, in combination with certain adverse
hydrogeologic conditions. For sites with this designation, the City of Edmonds requires a site -
specific geotechnical evaluation addressing the risk associated with the landslide hazard area and
providing specific recommendations concerning the development of the site in accordance with
the City of Edmonds geotechnical report requirements. The conclusions and recommendations
presented in this report are intended to address the concerns related to the landslide hazard
designation in general accordance with the Chapter 19.10 of the ECDC.
Provided that the recommendations presented in this report are implemented, the
proposed development is considered geotechnically feasible and is not anticipated to adversely
affect the stability of the site, the adjacent properties, or the surrounding area. It is our opinion
that the subject site will remain stable following development, as defined in Chapter 19.10.020-0
of the ECDC, which defines stable to mean "that the risk of damage to the proposed
development, or to adjacent properties, from soil instability shall be minimal and that the
proposed development will not increase the potential for soil movement." It should be
understood that the site is mapped within a portion of the North Edmond ESLHA having a 10 to
30 percent probability of movement in a 25 year period. Given the lateral extent, depth, and
topographic relief of the Meadowdale Landslide, it is our opinion that mitigation of this risk of
movement is not feasible. Chapter 19.10.020-0 of the City of Edmonds Building Code indicates
that. such a hazard shall not render a site proposed for single-family residences to be presumed
unstable for the purposes of this provision if the risk of probability of earth movement is
measured at 30 percent or less within a 25 year period.
Seismic Hazard Areas
Chapter 23.80.20 of the ECDC defines Seismic Hazard Areas as areas subject to severe
risk of damage as a result of earthquake -induced ground shaking, slope failure, settlement, soil
liquefaction, lateral spreading, or surface faulting. Our analyses indicate that the site is
susceptible to soil liquefaction during a design earthquake and has a 10 to 30 percent probability
of movement within 25 years associated with deep seated reactivation of the Meadowdale
Landslide mass. As such, it appears that the site meets the criteria for Seismic Hazard Areas as
established in Section 23.80.020 of the ECDC. A more detailed discussion of these risks is
presented in the Seismic Considerations and Slope Stability Considerations sections of this
report. Measures to reduce the risk of damage to the structure associated with seismic hazards
are presented in the Foundation Considerations, Backfilled Walls, and Slab -on -Grade Floor
sections of this report. In our opinion, the proposed development is considered geotechnically
feasible provided that the recommendations presented in this report are implemented.
Slope Stability Considerations
ZZA completed slope stability analyses for the site using the XSTABL5.2 computer
program. The stability analyses were based on a generalized subsurface profile taken down the
fall of the slope as shown on Figure 2. The soil profile consists of colluvium deposits over
' undisturbed Whidbey Formation deposits. Groundwater was modeled based on site specific
piezometric measurements completed during the winter of 2006.
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Static and pseudo -static (seismic) stability analyses were completed for three surface
profiles. These profiles are outlined below and presented on Figures 3 through 7.
• Figure 3 — Depicts the current configuration and stability of the slope for static
conditions.
• Figure 4 — Depicts the current configuration and stability of the slope for pseudo -static
conditions.
• Figure 5 — Depicts the configuration of the slope during construction for static conditions.
The profile and analysis includes the use of two temporary ecology block shoring walls,
as discussed in the Temporary Shoring section of this report.
• Figure 6 — Depicts the configuration of the slope after construction for static conditions.
• Figure 7 — Depicts the configuration of the slope after construction pseudo -static
conditions.
Our analyses of the current and post construction slope configurations were completed
for static and pseudo -static conditions. Our analyses used a pseudo -static coefficient (kh) of 0.17,
or %2 of Amax calculated in accordance with the procedures presented in the 2006 International
Building Code. Friction angles and cohesion values used in our analyses for each soil stratum
are presented on Figures 3 through 7. Based on the site specific boring data, it is our opinion that
the referenced friction angle and cohesion values are reasonable estimates of the site soil strength
parameters.
Factors of safety of 1.5 or greater under static conditions and 1.1 or greater under pseudo -
static conditions are generally considered acceptable for permanent structures and slopes. Static
safety factors of 1.1 or greater are generally considered acceptable for temporary structures and
slopes. Our analysis of the current slope configuration indicates static and pseudo -static safety
factors of about 2.2 and 1.1, respectively. Our analysis of the slope configuration during
construction indicates a static safety factor of about 1.6. Our analysis of the slope configuration
after construction indicates static and under pseudo -static safety factors of about 2.0 and 1.1,
respectively..
It should be noted that the slope stability analyses described above are associated only
with the subject site. These analyses and reported safety factors are not intended to represent
that stability of the larger scale Meadowdale Landslide mass. We evaluated the stability of the
larger scale Meadowdale Landslide mass by reviewing the 1979 Landslide Hazard Investigation
prepared by Roger Lowe Associates and the revised Landslide Hazard Map for the Meadowdale
Landslide Area prepared by Geoengineers in 1985. These publications indicate that the western
and eastern portions of the subject site have a 30 percent and 10 percent probability of movement
within an existing extensive slump during a 25 year period, respectively. Based on our site
specific subsurface explorations and our reconnaissance of the surrounding vicinity, it is our
opinion that the site conditions generally appear to be consistent with the conditions reported for
the mapped risk probabilities.
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The project plans indicate that a relatively small wedge of fill with a maximum thickness
of about 2 feet will be placed behind a retaining wall in the western portion of the upper level
parking area. Based on our evaluation, it is our opinion that this wedge of fill will not have a
significant effect on slope stability.
The landslide mechanisms modeled in our site specific slope stability analyses and the
mechanism indicated for the project vicinity in the Roger Lowe Associates and GeoEngineers
reports primarily consist of rotational/slump failures and deep seated rotational or complex
landslides. Our evaluation also considered other types of earth movement including debris
avalanches, earth flows, debris falls, and mud flows in accordance with the recommendations
presented in the 2007 Landau Associates report and the requirements of Chapter 19.10 of the
ECDC.
Our evaluation indicates that the base of a steep west -facing slope is located about 150 to
180 feet east of the subject parcel near the eastern side of Lot 8. This steep slope exhibited
geomorphic indications of surficial soil creep and shallow surficial landsliding. Based on our
observations and published geologic maps and geotechnical reports of the area, this steep slope is
interpreted as a portion of the Meadowdale landslide headscarp. Based on our review of City
files, portions of the headscarp appear to be susceptible to rapidly moving earth topples and
slides, and mud and debris flows. However, given the distance of the subject site from the base
of the slope and the relatively level ground surface of Lot 8, which would tend to act as a run -out
area and reduce the velocity of mass wasting material, it is our opinion that the risk of damage to
the subject site from landslide debris derived from the steep west -facing headscarp is low.
Site Preparation
We anticipate that this project will require cuts ranging from about 5 feet near the west
and east sides of the site to about 13 feet near the middle of the site. Site preparation should
include the removal of all vegetation, root mass, organic soils, existing structures, undocumented
fill material, and any deleterious debris from building and paving areas, or those locations where
"structural fill" is to be placed.
Preparation for site grading and construction should begin with procedures intended to
drain ponded water and control surface water runoff. It will be difficult to successfully utilize
on -site soils as "structural fill" if accumulated water is not drained prior to grading, or if drainage
is not controlled during construction. Attempting to grade the site without adequate drainage
control measures will reduce the amount of on -site soil effectively available for use, increase the
amount of select import fill materials required, and ultimately increase the cost of the earthwork
and foundation construction phases of the project.
Following clearing and grubbing, any organic -rich topsoil will need to be stripped in the
building and pavement areas, as well as those areas to receive structural fill. Based on our
explorations, topsoil (grass sod) on the order of 3 inches thick appears to mantle the site. The
' topsoil should be removed and should not be reused as structural fill. Localized areas of deeper
organics, such as root systems, may be encountered within the project site and should likewise be
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removed. Any excavations that extend below finish grades should be backfilled with structural
fill as outlined subsequently in this report. .
After stripping of topsoil and excavation to design grade is completed, the exposed soils
will generally consist of silty clay to clayey silt with variable sand content. Prior to placement of
structural fill, we recommend that foundation, floor subgrade, pavement areas, and other areas to
receive structural fill be proofrolled and compacted to a firm and unyielding condition in order to
achieve a minimum compaction level of 95 percent of the modified Proctor maximum dry
density as determined by the ASTM:D-1557 test procedure. Due to the silty nature of the
exposed soils, proofrolling and adequate compaction can only be achieved when the soils are
within approximately f 2 percent of the optimum moisture content. Soils which appear firm after
stripping may be proof -rolled with a heavy compactor, loaded double -axle dump truck, or other
heavy equipment under the observation of a qualified geotechnical engineer, or his
representative. This observer will assess the subgrade conditions prior to filling. Areas where
loose surface soils exist due to grubbing and stripping operations should be considered fill to the
depth of the disturbance and treated as subsequently recommended for structural fill placement.
The need for or advisability of proofrolling due to soil moisture conditions should determined at
the time of construction. We recommend that a representative of our firm observe the soil
conditions prior to and during proofrolling to evaluate the suitability of stripped subgrades prior
to fill placement.
Earthwork may be difficult or impossible during periods of elevated soil moisture and
wet weather due to the moisture sensitive nature of the silty and clayey site soils. Excavated site
soils may not be reusable as structural fill depending on the moisture content and weather
conditions at the time of construction. If soils are stockpiled for future reuse and wet weather is
anticipated, the stockpile should be protected with plastic sheeting that is securely anchored. If
on -site soils become unusable, it may become necessary to import clean, granular soils to
complete wet weather site work.
Subgrade soils that become disturbed due to elevated moisture conditions should be
overexcavated to expose firm, non -yielding, non -organic soils and backfilled with compacted
structural fill. We recommend that the earthwork portion of this project be completed during
extended periods of dry weather if possible. If earthwork is completed during the wet season
(typically November through May) it may be necessary to take extra precautionary measures to
protect subgrade soils. Wet season earthwork may require additional mitigative measures
beyond that which would be expected during the drier summer and fall months. This could
include diversion of surface runoff around exposed soils, draining of ponded water on the site,
and collection and rerouting of groundwater seepage from upgradient on- and off -site sources.
Once subgrades are established, it may be necessary to protect the exposed subgrade soils from
construction traffic. Placing quarry spalls, crushed recycled concrete, or clean pit -run sand and
gravel over these areas would further protect the soils from construction traffic.
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All fill material placed in building, pavement, and non -landscaped areas should be placed
in accordance with. the recommendations herein for structural fill. Prior to placement, the
surfaces to receive structural fill should be prepared as previously described. All structural fill
should be free of organic material, debris, or other deleterious material. Individual particle size
should be less than 3 inches in maximum dimension.
Structural fill should be placed in lifts no greater than 8 inches in loose thickness. The
structural fill should be compacted to at least 95 percent of the modified Proctor maximum dry
density as determined by the ASTM:D-1557 test procedure in building areas and to a depth of 2
feet below the subgrade surface in pavement areas. Below a depth of 2 feet in pavement areas,
the structural fill should be compacted to at least 90 percent of ASTM:D-1557. We recommend
that a representative from our firm be present during grading so that an adequate number of
density tests can be conducted as structural fill placement occurs. In this way, the adequacy of
the earthwork may be evaluated as it proceeds. In the case of roadway and utility trench filling
in municipal rights -of -way, the backfill should be placed and compacted in accordance with
current local codes and standards.
' The suitability of soils for structural fill use depends primarily on the gradation and
moisture content of the soil when it is placed. As the amount of fines (that soil fraction passing
the U.S. No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in
moisture content and adequate compaction becomes more difficult, or impossible, to achieve.
Generally, soils containing more than about 5 percent fines by weight (based on that soil fraction
passing the U.S. No. 4 sieve) cannot be compacted to a firm, non -yielding condition when the
' moisture content is more than a few percent from optimum. The optimum moisture content is
that which yields the greatest soil density under a given compactive effort.
At the time of the subsurface evaluation, the site soils disclosed by the explorations
appeared to have moisture contents above their estimated optimum moisture content relative to
their possible use as structural fill. Due to the high moisture sensitivity of the site soils, we
anticipate that adequate moisture control and compaction of these silty and clayey soils will be
difficult or impossible to achieve even under favorable weather conditions. We recommend that
the project include provisions for the export of on site cut soils and import of "clean" free
draining sand and gravel, as discussed below.
We recommend that import fill consisting of a "clean", free -draining pit -run sand and
gravel be used. Such material should generally contain less than 5 percent fines, based on that
soil fraction passing the U.S. No. 4 sieve, and not contain discrete particles greater than 3 inches
in maximum dimension. It should be noted that the placement of structural fill is, in many cases,
weather -dependent. Delays due to inclement weather are common even when using select
granular fill. We recommend that site grading and earthwork be scheduled for the drier months,
if at all possible.
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We anticipate that temporary open cuts may be utilized during the construction of
foundation elements for the proposed structure. Temporary slope stability is a function of many
factors, including the following:
1. The presence and abundance of groundwater;
2. The type and density of the various soil strata;
3. The depth of cut;
4. Surcharge loading adjacent to the excavation; and
5. The length of time the excavation remains open.
It is exceedingly difficult under the variable circumstances to pre -establish a safe and
"maintenance -free" temporary cut slope angle. Therefore, it should be the responsibility of the
contractor to maintain safe slope configurations since the contractor is continuously at the job
site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface
materials and groundwater conditions encountered. It may be necessary to drape temporary
slopes with plastic or to otherwise protect the slopes from the elements and minimize sloughing
and erosion. We do not recommend vertical slopes or cuts deeper than 4 feet if worker access is
necessary. The cuts should be adequately sloped or supported to prevent injury to personnel
from local sloughing and spalling. The excavation should conform to applicable Federal, State,
and local regulations.
According to Chapter 296-155, Part N, Excavation Trenching and Shoring, of the
Washington Administrative Code (WAC), it is our opinion that the existing colluvial soils
encountered at the site within the planned cut depths are representative of a WAC Type C soil.
According to the Code, excavations less than 20 feet deep in Type C soils may be cut at a
maximum temporary slope angle of 34 degrees (1 %2H:1 V).
Zones of perched groundwater may be encountered during site excavation. This
condition may require the use of flatter temporary slopes or the use of additional temporary
shoring. Alternatively, it may be feasible to allow the area(s) to drain prior to continuing the
excavation.
The stability of temporary slopes is affected by the length of time the excavation remains
open. The design and construction schedule should make every effort to minimize the time
excavations remain open. It may be necessary to backfill temporary cut slopes if the project
experiences protracted delays.
Temporary Shoring
Based on our review of the preliminary project plans, the WAC temporary cut slope
inclination of 1'/2H:IV, and our slope stability analyses, it appears that temporary shoring will be
required for portions of the north, south, and eastern sides of the lower level, and along the
eastern property line. Several temporary shoring options have been considered for this project
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including cantilever soldier pile walls, cantilever sheet pile walls, and gravity walls such as
concrete ecology block and Ultra Block walls. We understand that ecology block walls are the
preferred type of temporary shoring wall. Based on the subsurface conditions encountered in our
explorations, we recommend that a maximum wall height of 6 feet and a wall batter of 1H:5V be
used for planning purposes. Based on our slope stability analyses, we recommend that the
project plans include 6 foot high temporary ecology block walls behind the northern, southern,
and eastern lower level subgrade walls and along the eastern property line.
We anticipate that it will be extremely difficult to remove these temporary shoring walls
once permanent cast -in -place concrete walls are constructed. We recommend that the project
plans and budget include provisions for abandoning the ecology walls in place behind the
permanent cast -in -place walls. ZZA is available to provide additional geotechnical engineering
recommendations and/or design services for temporary ecology block gravity shoring systems.
' Permanent Slopes
Permanent cut and fill slopes should be constructed no steeper than 2H:IV, provided that
' all embankment fill is compacted to at least 90 percent of the modified Proctor maximum dry
density as determined by the ASTM:D-1557 test procedure. It has been our experience that
permanent slopes steeper than 2H:1 V will tend to ravel and slough to a flatter inclination over
' time. In addition, with steeper slopes, topsoil erodes readily and it is more difficult and takes
longer to establish vegetation for slope protection.
All permanent slopes should be provided with deep-rooted ground cover immediately
after they are completed. If the time of year does not allow the growth of stabilizing vegetation,
finished slopes should be provided with temporary erosion protection. Temporary erosion
protection could include the use of anchored sheet plastic or rolled erosion protection material,
such as Jute matting or Curlex II, if vegetation has not been established by the regional wet
season (typically November through May).
Foundation Considerations
We understand that the preliminary design included the use of conventional shallow
spread foundations. In our opinion, conventional spread footings will provide adequate support
for the planned structure, provided that the subgrade is prepared in accordance with the
recommendations presented below and that the potential for liquefaction induced settlement is
considered acceptable.
As discussed in the Seismic Considerations section of this report, we estimate that total
liquefaction induced settlements on the order of 1 to 2 inches could be experienced at the site
during a design earthquake. Differential seismic induced settlements could approach''/2 to 1 inch
over a distance of about 30 feet. If the risk of seismic induced settlement is not considered
acceptable, we recommend that the house be supported on piles. ZZA is available to provide
design recommendations for pile foundations, if needed.
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Based on our subsurface explorations, we anticipate that shallow foundations will be
underlain by about 30 feet of colluvial soils primarily consisting of medium stiff, silty clay with
' variable sand content and loose to medium dense sand with variable silt content. To reduce total
and differential static settlements to tolerable levels and provide a firm subgrade, we recommend
that the upper 24 inches of the foundation subgrade be compacted to a firm and unyielding
condition and to at least 95 percent of the modified Proctor maximum dry density as determined
by the ASTM:D-1557 test procedure. If soil moisture conditions will not allow for this level of
compaction, the subgrade soils should be removed to a depth of 24 inches below the bottom of
' the foundation and replaced with structural fill compacted to a firm and non yielding condition
and to at least 95 percent of the modified Proctor maximum dry density. The overexcavation
should extend laterally beyond the edge of the footing a distance equal to the depth of the
' overexcavation.
Continuous or isolated column footings founded as described above may be designed for
' a maximum allowable bearing pressure of 2,000 psf. A one-third increase in this bearing
pressure may be used for short-term wind or seismic loading. For building and retaining wall
foundations, we recommend using an allowable base friction value of 0.35 and a maximum
tallowable passive resistance of 230 pcf. The allowable base friction and passive resistance
values include a safety factor of 1.5. Exterior footings should extend at least 18 inches below
adjacent grade for frost protection, while the interior footings should extend at least 12 inches
' below adjacent grade. We recommend that all continuous and isolated footings be at least 16 and
18 inches in width, respectively.
' We estimate that the total static settlement of foundation members supported as
recommended above may approach 1 inch. Static differential settlement of foundations could
approach %2 inch over a distance of 30 feet. Settlements would occur elastically as the loads are
applied. As previously discussed in the Seismic Considerations section of this report,
foundations may be subject to total seismic settlements on the order of 1 to 2 inches. Seismic
differential settlement of foundations could approach 'h to 1 inch over a distance of 30 feet. We
recommend that the structural engineer include provisions in the foundation design to minimize
the adverse effects of potential seismic induced differential settlement.
' Foundation settlement is oftentimes a function of the condition of the footing excavation
subgrade. Footing excavations should be free of loose or soft soil, slough, debris, or water prior
' to pouring footing concrete.
The moisture sensitive nature of the on -site soils may require that the footing excavations
' be covered with a lift of crushed rock or a lean concrete "mud mat" to minimize disturbance of
the bearing surface during construction in wet weather. Under no circumstances should footings
be cast atop loose or soft soil, slough, debris, or surfaces with standing water. We recommend
' that a representative from our firm observe the condition of the footing subgrades prior to the
pouring of concrete, or a lean concrete mud mat, in order to confirm that the bearing soils are
undisturbed and that conditions are consistent with the recommendations contained within this
' report.
1
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Backfitted Walls
Preliminary plans indicate that the residence will be constructed in close proximity to the
property lines and that temporary open cuts and shoring will be required to complete the planned
excavations for the structure. In order to reduce the distance that project excavations extend into
the slope and the height of the resulting cut slopes and shoring walls, we recommend that the
subgrade walls (particularly the north, south, and eastern walls for the lower level) be designed
in a manner that will minimize the length of the "heel", or that portion of the wall footing that
extends toward to slope.
As discussed in the Temporary Cut Slope section of this report, the stability of temporary
cuts is affected by the length of time the cut remains open. To reduce the length of time
temporary cuts remain open, we recommend that backfilled walls for the structure be designed in
a manner that will allow for the placement of wall backfill before the placement of structural
framing and floors, or that the design include provisions for temporary bracing. Further, we
recommend that the structural engineer specify a minimum concrete cure time or minimum
concrete unconfined compressive strength that should be attained before subgrade walls are
backfilled.
All backfill placed behind walls or around foundation elements should be placed in
accordance with our recommendations for structural fill. The following recommended earth
pressures, presented as equivalent fluid weights, are based on the assumption of a level backfill
surface and no buildup of hydrostatic pressure behind the wall. To minimize lateral earth
pressures and prevent the buildup of hydrostatic pressures, the backfill within 24 inches of the
wall should contain less than 5 percent fines, based on that portion passing the U.S. No. 4 sieve,
coupled with a perforated pipe drain placed at the base of the wall backfill, similar in
configuration to that described for the perimeter footings. We anticipate that the lower level of
the structure may experience moderate groundwater seepage. We recommend that 6-inch
diameter drain pipes be used for the lower level of the structure. The wall drain system should
include'permanent cleanouts to allow for potential. future maintenance of the system. The upper
1-foot of the wall backfill should consist of a low permeability silty soil and be sloped away
from the wall in order to reduce the potential for surface water infiltration behind the wall.
If the backfilled walls are structurally restrained from lateral movement at the top, we
recommend that they be designed for an "at -rest" equivalent fluid weight of 55 pounds per cubic
foot (pcf). If the top of the wall is free to move laterally in an amount equal to at least 0.1
percent of the wall height during placement of backfill soils, they may be designed for an
"active" equivalent fluid weight of 35 pcf.
We recommend uniform 'seismic surcharges equivalent to 7H in pounds per square foot
' (rectangular distribution) for yielding walls and I I for walls structurally restrained from lateral
movement, where H is the height of the wall above finished grade in feet.
' Surcharges due to sloping ground, adjacent footings, vehicles, construction equipment,
etc., must be added to these values. The above equivalent fluid pressures assume that the
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' backfill is compacted to approximately 90 to 92 percent of the modified Proctor maximum dry
density determined in accordance with ASTM:D-1557. Additional compaction adjacent to the
' wall will increase the earth pressure, while a lesser degree of compaction could result in post
construction settlements.
Slab -On -Grade Floors
In our opinion, the use of slab -on -grade concrete floors is geotechnically feasible
provided that the subgrade is prepared in accordance with the previous site preparation
recommendations and the potential for liquefaction induced settlement is considered expectable:
' As previously discussed in the Seismic Considerations section of this report, slab -on -grade floors
may be subject to total liquefaction induced surface settlements on the order of 1 to 2 inches.
We recommend that the structural engineer make provisions in the floor design to minimize the
' adverse effects of a potential seismic induced differential settlement on the order of 'h to 1 inch
over a distance of about 30 feet.
' All slab -on -grade floors should be founded on proofrolled or compacted native ground or
structural fill compacted to at least 95 percent of the modified proctor maximum dry density
determined in accordance with ASTM:D-1557. We recommend that slab -on -grade floors be
underlain by a minimum 6-inch thickness of clean, free draining, well graded mixture of course
sand and gravel to provide uniform support and act as a capillary break. The capillary break
material should contain less than 3 percent fines, based on that portion passing the U.S. No. 4
' sieve.
In floor slab areas where moisture sensitive floor coverings are planned, an impermeable
' membrane (e.g. polyethylene sheet) should be placed directly beneath the slab to act as a vapor
retarder. The vapor retarder should be installed in accordance with ASTM E 1643 "Standard
Practice for Installation of Water Vapor Retarders Used in Contact with Earth or Granular Fill
' Under Concrete Slabs". We recommend a minimum 10-mil polyethylene thickness, or the
minimum thickness specified by the flooring manufacturer, whichever is greater. When concrete
slabs are cast directly over polyethylene vapor retarders, the concrete water -to -cement ratio must
' be correctly specified in order to control bleed water and plastic shrinkage cracking.
Drainage Considerations
' We recommend that the building be protected by a perimeter footing drain. The drain
should consist of a minimum 4-inch diameter perforated pipe embedded in at least an 18-inch
' wide envelope of clean, free -draining, well graded mixture of course sand and gravel. The free -
draining materials should contain less than 5 percent fines, based on that soil fraction passing the
U.S. No. 4 sieve. A non -woven filter fabric such as Mirafi 140N, or equivalent, should envelope
' the free -draining granular material.
We recommend that an under -slab drainage system be installed below the lower level and
' "Virtual Golf' area concrete slab floors. The drainage system should consist of perforated drain
lines placed below the capillary break material of the lower level concrete slab floor. The drain
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lines should be equally spaced on approximately 15 foot centers and should consist of 6-inch
diameter, perforated PVC drain pipe placed in excavations 1 foot deep and 1 foot wide. The
trenches should be lined with a non -woven filter fabric such as Mirafi 140N, or equivalent. The
trench should be backfilled with a clean, free -draining, well graded mixture of coarse sand and
gravel contain less than 3 percent fines, based on that soil fraction passing the U.S. No. 4 sieve.
Subsurface drainage systems including the perimeter footing drains, wall drains, and
under -slab drains should include permanent cleanouts to allow for potential future maintenance
of the systems. Under -slab drains may be connected to the footing drain system. Roof drains
should not be connected to the subsurface drainage system. The roof and footing drain system
should be tightlined to a City approved discharge location.
Final exterior grades should promote free and positive drainage from the building area at
all times. Water must not be allowed to pond or to collect adjacent to foundations or within the
immediate building area. We recommend a gradient of at least 2 percent be provided for a
minimum distance of 5 feet from the building perimeter, except in paved areas. In concrete or
asphalt paved areas, a minimum gradient of one-half percent should be provided unless
provisions are included for the collection and disposal of surface water adjacent to the structure.
CLOSURE
The conclusions and recommendations presented in this report are based on the
explorations accomplished for this study. The number, location, and depth of the explorations
were completed within the site and scope constraints of the project so as to yield the information
necessary to formulate our recommendations. The plans for this project were in the preliminary
stage at the time this report was written. Under the circumstances, it is recommended that we be
provided the opportunity for general review of the project plans and specifications in order to
confirm that the recommendations and design considerations presented in this report have been
properly interpreted and implemented into the project design package.
The integrity and performance of the foundation systems at this site depend on proper site
preparation and construction procedures. Field judgment by a qualified engineer will be
necessary in order to determine the adequacy of the site grading, drainage, and foundation
support systems. Therefore, because of our familiarity with the site soils, we recommend that
Zipper Zeman Associates, Inc. be retained to provide geotechnical services during the earthwork
and foundation construction phases of the project. If variations in the subsurface conditions are
observed at the time of construction, we would be able to provide additional geotechnical
engineering recommendations to the contractor and owner in a timely manner as the project
construction progresses.
81052440 Johnson Res Report 053008.doe
Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
81052440
May 30, 2008
Page 22
We appreciate this opportunity to be of service to you, and would be pleased to discuss
the contents of this report or other aspects of the project with you at your convenience.
6
EXPIRES _ 04 / 03 / 10
1 U15l°,'
Respectfully submitted,
Zipper Zeman Associates, Inc.
James P. Georgis, L.E.G.
Project Geologist
James B Thompson, P.E.
Principal
Enclosures: Figure 1 — Site and Exploration Plan
Figure 2 — Generalized Geologic Cross Section A -A'
Figure 3 — Static Slope Stability Analysis — Existing Conditions
Figure 4 — Pseudo -Static Slope Stability Analysis — Existing Conditions
Figure 5 — Static Slope Stability Analysis — Construction Conditions
Figure 6 — Static Slope Stability Analysis — Post Construction Conditions
Figure 7 — Pseudo -Static Slope Stability Analysis — Post Construction Conditions
Appendix A.— Field Exploration Procedures and Logs
Appendix B — Laboratory Test Procedures and Results
81052440 Johnson Res Report 053008.doc
\ HOUSE
EASEMENT \ #16121 cd I � , ' l I I I/ II LEGEND:
o o I II II I I I I I
B-1 BORING NUMBER AND
30' J\ \ \ / I I I I I I I 1 APPROXIMATE LOCATION
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0 20 40
SCALE IN FEET
LEGEND:
B-1
BORING NUMBER
TOP OF BORING
7
STANDARD PENETRATION RESISTANCE IN BLOWS PER FOOT
ST
SHELBY TUBE SAMPLE
ATD =
GROUNDWATER LEVEL AT TIME OF DRILLING
10/9/06 V
GROUNDWATER LEVEL ON DATE INDICATED
BOTTOM OF BORING
NOTES:
THE STRATA ARE BASED UPON INTERPOLATION
BETWEEN EXPLORATIONS AND MAY NOT REPRESENT
ACTUAL SUBSURFACE CONDITIONS. SIMPLIFIED NAMES
ARE SHOWN FOR SOIL DEPOSITS BASED ON
GENERALIZATIONS OF SOIL DESCRIPTIONS.
SEE EXPLORATION LOGS AND'REPORT TEXT FOR MORE
DETAILED SOIL AND GROUNDWATER DESCRIPTIONS.
0 20 40
SCALE IN FEET
I-
W
W
IL
Z
Z
O
H
W
J
W
A
120 -,
100 -
40 -
20 -
a
PROPOSED -
RESIDENCE
R
B-1
EXISTING GROUND
SURFACE
I
EXISTING RESIDENCE
16121 34TH PLACE WEST
'
FF EL. 101.5'
74TH PLACE WEST
FF EL.
92'
5 I
s
7
ST
FF EL
82.2'
10/9/06
12 1 U46/006
8
_
_
11/16/O6
y �
10/9/06
=
i
ST
6
20 i
Medium stiff to stiff, silty
8
CLAY to clayey SILT with
cf
variable sand content and
13
loose SAND with variable
i
18
silt content. (Colluvium)
-t4
i
25
18
i
35
i
26
Very stiff to hard, massive
to finely laminated, clayey
27
SILT. (Whidbey Formation)
I
Loose to medium dense
�
24
SAND with variable silt
content.
(Possible Colluvium)
i
Medium dense, interbedded,
silty SAND and sandy SILT.
(Possible Colluvium)
ZZA
Zipper Zeman Associates, Inc. Project No: 81052440,Geotechnical and Environmental ConsultingDrawn by:J. Duncan
18905 33rd Avenue West, Suite 117
Lynnwood, Washington 98036 Date: May 2008
Tele: (425) 771-3304 Fax: (425) 771-3549 Scale: As Noted
A'
r 120
100
:1
F-
W
W
W
Z
60 p
F-
W
J
W
40
20
rN
Johnson Residence
Edmonds, Washington
FIGURE 2 - GENERALIZED
GEOLOGIC CROSS SECTION A -A'
125
100
a 75
a�
X
Q 50
25
A
Existine Slone Conditions - 10 most critical surfaces
Existing
Minimum Bishop FOS for Static Conditions = 2.2 Foundation
Surcharge
0 25 50 75 .100 125 150 175 200
X—AXIS (feet)
SOIL PROPERTIES
(1)
Colluvium, 0=0
C=900 psf
(2)
Colluvium, 0=32 °,
C=0 psf
(3)
Colluvium, 0=36 °,
C=0 psf
(4)
Whidbey Formation,
0=0 °, C=2000 psf
125
(
a 75
aD
cn
X
Q 50
C
25
rel
Existine Slobe Conditions - 10 most critical surfaces
Existing
Minimum Bishop FOS- for Pseudo -Static Conditions = 1.1 Foundation
Surcharge
0 25 50 75 100 125 150 175 200
X—AXIS (feet
SOIL PROPERTIES
(1)
Colluvium, 0=0
C=900 psf
(2)
Colluvium, 0=20 °,
C=0 psf
(3)
Colluvium, 0=36 °,
C=0 psf
(4)
Whidbey Formation,
0=0 °, C=2000 psf
125
100
a 75
aD
y--
N
X
Q 50
25
C+A
Slone Conditions During Construction - 10 most critical surfaces
Existing
Minimum Bishop FOS for Static Conditions = 1.6 Foundation
Surcharge
0 25 50 75 100 125 150 175 200
X-AXIS (feet)
SOIL PROPERTIES
(1)
Colluvium, 0=0
C=900 psf
(2)
Colluvium, 0=32 °,
C=0 psf
(3)
Colluvium, 0=36°,
C=Opsf
(4)
Whidbey Formation,
0=0 °, C=2000 psf
125
100
a 75
a>
cn
X
Q 50
25
X
Post Construction Slone Conditions - 10 most critical surfaces
Existing
Minimum Bishop FOS for Static Conditions = 2.0 Foundation
Surcharge
0 25 50 75 100 125 150 175 200
X—AXIS (feet)
SOIL PROPERTIES
(1) Colluvium, 0=0
C=900 psf
(2) Colluvium, 0=32 °,
C=0 psf
(3) Colluvium, 0=36 °,
C=0 psf
(4) Whidbey Formation,
0=0 °, C=2000 psf
125
100
a 75
a�
V)
X
Q 50
25
N
Post Construction Slope Conditions - 10 most critical surfaces
Minimum Bishop FOS for Pseudo -Static Conditions = 1.1
Existing
Foundation
Surcharge
0 25 50 75 100 125 150 175 200
X—AXIS (feet)
SOIL PROPERTIES
(1)
Colluvium, 0=0
C=900 psf
(2)
Colluvium, 0=20 °,
C=0 psf
(3)
Colluvium, 0=36 °,
C=0 psf
(4)
Whidbey Formation,
0=0 °, C=2000 psf
APPENDIX A
FIELD EXPLORATION PROCEDURES AND LOGS
APPENDIX A
FIELD EXPLORATION PROCEDURES AND LOGS
81052440
Our field exploration for this project included 2 borings completed on June 22,
2006. The approximate exploration locations are shown on the Site and Exploration
Plan, Figure 1. The exploration locations and elevations were taken from a site specific
' survey completed by Greene Land Surveying dated August 8, 2006. Descriptive logs of
the explorations are enclosed in this appendix. The following sections describe our
procedures associated with the exploration.
' The exploratory borings
p ry were advanced with a hollow stem auger, using a track -
mounted drill rig operated by an independent drilling company working under subcontract
to ZZA. An experienced geologist from our firm continuously observed the borings,
logged the subsurface conditions encountered, and obtained representative soil samples.
' All samples were stored in moisture -tight containers and transported to our laboratory for
further visual classification and testing. After each boring was completed, the borehole
was backfilled with bentonite and soil cuttings.
Throughout the drilling operation, soil samples were obtained at 2.5- to 5-foot
depth intervals by means of the Standard Penetration Test (ASTM: D-1586). This testing
' and sampling procedure consists of driving a standard 2-inch outside diameter steel split
spoon sampler 18 inches into the soil with a 140-pound hammer free falling 30 inches.
The number of blows required to drive the sampler through each 6-inch interval is
recorded, and the total number of blows struck during the final 12 inches is recorded as
the Standard Penetration Resistance, or "blow count" (N value). If a total of 50 blows is
struck within any 6-inch interval, the driving is stopped and the blow count is recorded as
' 50 blows for the actual penetration distance. The resulting Standard Penetration
Resistance values indicate the relative density of granular soils and, the relative
consistency of cohesive soils.
The enclosed boringlogs describe the g vertical sequence of soils and materials
encountered in each boring, based primarily upon our field classifications and supported
' by our subsequent laboratory examination and testing. Where a soil contact was observed
to be gradational, our logs indicate the average contact depth. Where a soil type changed
' between sample intervals, we inferred the contact depth. Our logs also graphically
indicate the blow count, sample type, sample number, and approximate depth of each soil
sample obtained from the boring, as well as laboratory tests performed on these soil
' samples. If groundwater was encountered in a borehole, the approximate groundwater
depth, and date of observation, are depicted on the log.
' Groundwater observation wells were installed in borings B-1 and B-2. The
observation wells consisted of a length of slotted 1-inch PVC pipe placed in the borehole.
A blank PVC riser extended from the lower slotted section to the ground surface.
1
1
1
1
1
1
1
Washed silica sand was utilized to backfill the annular space between the slotted interval
and the borehole to allow entry of water into the well, while a mixture of bentonite was
used to backfill around the blank riser. A concrete surface seal and metal monument
cover were placed at the surface. Groundwater levels measured in the observation wells
subsequent to completion of drilling are indicated on the log, along with the date of
measurement. This information is also discussed in the text.
The boring logs presented in this appendix are based upon the drilling action,
observation of the samples secured, laboratory test results, and field logs. The various
types of soils are indicated as well as the depth where the soils or characteristics of the
soils changed. It should be noted that these changes may have been gradual, and if the
changes occurred between samples intervals, they were inferred.
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-1 PAGE 1 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 90.5 Feet
Soil Description ai � -0 Penetration Resistance rn
C
w c a as a; c
0 ~ = Standard Blows per foot Other j F
Z Z
0 10 20 30 40 5
0 Grass - so
Medium stiff, moist to wet, gray -brown, silty CLAY with ------------- - - -- - -- - I i
; - -
some fine sand. Slight iron oxide staining. Blocky,
disturbed texture. (Colluvium) ------------
- - -
I I
J__+__� __I___'__J_
I f I I
5
J.
S-1
.--�--r-----I-- j--'F '- r-
-I---I---
(Moistunit weight 95.5 pCf) S-1A •'
T__F__�
--------------
'
-
10 _
't--L--�-----I-- '--+--'---'---
1-inch thick sand seam observed at 11 feet. S-2
(Colluvium) PP = 3.25 tsf _ ' &; ; 8 Att.
_ J _ _ _
11/16/06
J IT_ _ _ _ _ I---
- — ---------- 10/9/06
1 5 __ 1
_ _ -
�' Loose, saturated, gray, silty SAND with trace fine _____ ______ S 3 nTD 6 20OW
organic material. (Colluvium)
-------------
- --------------------------------------------------------------
----------- - -
Medium stiff, wet, gray, silty CLAY with trace to some
20 fine sand. Disturbed, blocky texture with inclusions of --
T
hard, angular clayey SILT. (Colluvium) S-4
PP = 3.5 tsf 8
-------------
'�__J_
, f
25
Explanation
Monitoring Well Key Moisture Content
I2-inch O.D. split Spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
3-inch LD Shelby tube sample ® Bentonite
Testing Key
® No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Att. = Atterberg Limits
ATD or date of measurement
UCT = Unconfined Compression Test
ZZA ❑ Blank Casing PP = Pocket Penetrometer
7ipner Zeman Acco iat c, Inc. BORING LOG Figure A-1
Geotechnical and Environmental Consulting Date Drilled: 06/22/2006 Logged By: JPG
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-1 PAGE 2 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 90.5 Feet
9
Soil Description
-o
Penetration Resistance
y
oM
N
Standard Blows per foot Other
Z
0 10 20 30 40 5
Z
25
Grades to stiff and moist to wet.
PP = 3.5 tsf
_--i-__
S-5
•I
13
Att.
.
_______________________________________________
Loose to medium dense, saturated, gray, silty, fine
_____________
S-6
_ _ _ _ r r _ - 1- _ -1 - _ - - _ T
1
' I ' i
L
14
30
SAND. (Colluvium)
_____________
--7- - �--I---�--'l--'1--r--�- -I - - -
I I I I -
35
Grades to medium SAND with trace silt.
Medium dense, saturated, gray, interbedded, silty, fine
to medium SAND and fine sandy SILT.
--- T
-------------:+'
S-7
:•.
:::
A '
_ _ J _ _ L _ _
-r--� --
I
J -' -- ' - - '
--
8
200W
(Possible Colluvium)
40
1-inch thick organic seam observed at 40.5 feet.
--------------
-•-•
..
,� �•
, , :
18
Grades to silty, fine SAND.
S-9
-'�
�'•�
' ' I I '
*
20
45
Grades to interbedded, silty, well graded SAND with
:.;
trace clay and fine to medium SAND.
Very stiff, saturated, gray, thinly bedded SILT with26
--- ------
"'
T
- - -
trace to some fine sand. (Whidbey Formation)
'
_ _
I I I I I I_ -
I
50
I
Explanation
Monitorinq Well Key Moisture Content
2-inch O.D. split spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
3-inch I.D Shelby tube sample ® Bentonite
Testing Key
® No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Att. = Atterberg Limits
ATD or date of measurement
UCT = Unconfined Compression Test
El Blank Casing PP = Pocket Penetrometer
s� 7ipner Zeman Acco iat , Inc.
Geotechnical
.BORING LOG
Figure A-1
Date Drilled: 06/22/2006
Logged By: JPG
and Environmental Consulting
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-1 PAGE 3 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 90.5 Feet
Soil Description
Penetration Resistance
a a
a
v
a;
Q
ea
C
0
Standard Blows per foot Other
j
N
N Z
Z
50
0 10 20 30 40 5
Grades to very stiff, moist, greenish -gray, clayey SILT. 1
inch thick overconsolidated organic seam observed at
50.5 feel
I
S-11
;{
1
27
-------------
r:.•:-'
- F" - -I- - -' - - - - �' - -'- - -'- - -I - - -
-55
Grades to moist to wet, gray, finely laminated, clayey
SILT. PP = 4.5 tsf
___
T
___---------
S-12
;..
::.:.
L I
--i --i --i----- I--r--i --I---i---
_ _ r _ _ i_ _ _I _ _ _ _ r _ _
_ r
24
Boring completed at 56.5 feet on 06122/2006.
Groundwater observed at 15.5 feet at time of drilling.
Groundwater measured at 12.6 feet on 10/09/2006.
-------------
- - ;
Groundwater measured at 11.4 feet on 11/16/2006.
------------
- -
- 60------------
- -
�-
_____________
I
- r --
------ -------
------- ------
-------------
I
- - -
I I
1 I I
- 65
I
__
____________
---------------
_____-_____
------------
- 70
------ _-----
-------
1
________----
_ 1 _ _'_ _ _ I_ _ _' _ _ J _ _ _ _ L
_____________
I I
--r--,---
- 75
Explanation
Monitorinq Well Key Moisture Content
2-inch O.D. split spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
3-inch I.D Shelby tube sample ® Bentonite
Testing Kev
® No Recovery N Grout/Concrete GSA = Grain Size Analysis
20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Aft. = Atterberg Limits
ATD or date of measurement UCT = Unconfined Compression Test
❑ Blank Casing PP = Pocket Penetrometer
ZZA Zipper Zeman Associates., Inc.
Geotechnical
BORING LOG
Figure A-1
and Environmental Consulting
Date Drilled: 06/22/2006
Logged By: JPG
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-2 PAGE 1 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 103 Feet
Soil Description
d t
Penetration ResistanceCL
rn
o v
o.
`m
M
rn
oN
N Z
Standard Blows per foot Other
j
0 10 20 30 40 5
Z
~
----------------------------------------------
1
Medium stiff, moist to wet, mottled gray -brown silty ------------- - - -
CLAY with some sand. Disturbed, blocky texture.
(Colluvium)
1 ,
I '
_____________
5 -
S-1 I. 1 ' 1 I I 7
------------------------------ _ _ _ _ ___----------------- ----- -
Loose, moist, gray -brown, fine SAND with some silt. - L ' - - - - r - - F -'- - - - -
Slight to moderate iron oxide staining. (Colluvium)
r.__1__ _,__ i. .___I___'___
__________________________________________ r _
Medium stiff, wet, mottled gray -brown clayey SILT with 5
some sand. Disturbed, blocky texture. (Colluvium) 3.2 r- --- - -I
� � � ,
_I_ _ y _ _ 1 _ _ 1• _ _ I_ _ _,_ _ _
________________________________________________
10 Stiff, moist to wet, gray, clayey SILT. Disturbed, blocky -
texture with inclusions of hard, clayey SILT. S-3
(Colluvium) PP = 3.5 tsf g
., _ _ I _ - L
_____________
T
__ ---,--�--� --r--i---I--'--�--i -
-
-------------- --- y, silty,
AND. (Colluvium)---- ------- --- S-4 - 7
Loose, saturated, gray, silty, fine SAND. (Colluvium) ATD
-- ---i--'+--T----I---'---i--1--r--
--------------
15 I
S-5 T I I
------------------------------------------------ I 1 1
Medium still to stiff, moist, gray, clayey SILT with trace ----- - ----- _ - _;_ _ _I _ _ i _ _ ! _ _ _ _'_ _ _ _ .!
fine sand. Blocky texture. (Colluvium) PP = 3 tsf
I I •
Wet unit weight = 118 pcf ___ __ I _ _ J - - L-------------------------------------------------
Loose, saturated, gray, silty, fine SAND. (Colluvium)
_______________________________________________ _____
Stiff, moist, gray, finely laminated, clayey SILT. J _ _
(Colluvium) S-6 A 12
20 - 11/16/06
--T--
Grades to saturated, interbedded, finely laminated, S-7 1o/s/os
clayey SILT and fine, sandy SILT. PP = 2.5 tsf ----- - -
I
------------- I_
____________________________________________ _ I I ' '
Medium dense, saturated, gray, fine SAND with some -------------
silt. (Possible Colluvium)
- 25
Explanation
Monitoring Well Key Moisture Content
I2-inch O.D. split spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
3-inch I.D Shelby tube sample ® Bentonite
Testing Key
® No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Aft. = Atterberg Limits
ATD or date of measurement UCT = Unconfined Compression Test
ZZA ❑ Blank Casing PP = Pocket Penetrometer
Tipper Zeman Associates, Inc. BORING LOG Figure A-2
Geotechnical and Environmental Consulting Date Drilled: 06/22/2006 Logged By: JPG
UCT I
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-2 PAGE 2 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 103 Feet
aai
25
Soil Description
aCL
N
d
Z
o
o f0
Penetration Resistance
0
Standard Blows per foot Other
0 10 20 30 40 5
H
Z
c
y
~
Grades to fine sandy SILT.
Grades to silty fine SAND. 3-Inch thick, stiff, clayey
SILT seam observed at 30.5 feet.
Grades to loose, silty SAND with trace clay.
----------------------------- ----------------
Very stiff, moist to wet, gray, finely laminated, clayey
SILT with trace fine sand partings.
(Whidbey Formation)
PIP >4.5tsf
J: -----
_____________
--
--------------
-------------
--------------
-
-- -
S-80000
g
S_10
S11
S-12
S 13
00
00
00
00
Co
100
:.:
_:;.:
-
I I 1 I 1
I i
r _. _ 1
- _ - - -*- - t - - r ''- -
-
---+-- - - ---- ---'---
, I 1 -, -- I - --- I ,
-- -• L- -- --1-- _ - - -
-
I
r
T
_ _ L _ _ r _ _I- _ y _ L
' I I
1 ' I i
t I I 1
1_ ' _ J _ ' _ L _ _ I _ _I
----------''--T---------,--
I I
IL _ _ I_ _ _ _ _ y _ _ _
'
I ' I
I I 1
T
g
18
25
30
40
45
- 50
Explanation
Monitorino Well Key Moisture Content
2-inch O.D. split spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
0 1
3-inch I.D Shelby tube sample ® Bentonite
Testing Key
® No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Aft. = Atterberg Limits
ATD or date of measurement UCT = Unconfined Compression Test
❑ Blank Casing PP = Pocket Penetrometer
ZZA
7ipner Zeman Associates, Inc.
Geotechnical and Environmental Consulting
BORING LOG
Figure A-2
Date Drilled: 06122/2006
Logged By: JPG
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-2 PAGE 3 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 103 Feet
Soil Description
L
Penetration Resistance
`m
w
m
�
oM
F-
N Z
0
Standard Blows per foot Other
Z
0 10 20 30 40 5
50
Grades to hard, moist, gray, finely laminated, clayey
SILT. PP > 4.5 tsf
- -
--
S-14
♦
T
-------
35
Boring completed at 51.5 feet on 06/22/2006.
Groundwater observed at 13.5 feet at time of drilling.
Groundwater measured at 20.3 feet on 10/09/2006.
- -
Groundwater measured at 19.3 feet on 11 /16/2006.
--------------
I 1
55
-------------
-------------
_____________
-------------
-------------
1
,--
I
1 i
__ 1__ r__I__-,___
60
-------------
_____________
- -
_ _ L _ _'_ _ _I _ _ _ - 1 _ _ ' I_
r_ _I --
1 I I
_____________
I � I �
I I
-
_____________
-------------
_ _ _ _ ----1--�--�--r--i --
1 1
65
------------- -------------
_____________
-------------
___r__I__y__T__-
- 70
_____________
-------------
-------------
-------------
I
_____________
- 75
Explanation
Monitoring Well Key Moisture Content
I2-inch O.D. split spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
Tr 3-inch LD Shelby tube sample ® Bentonite
Testing Kev_
® No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Aft. = Atterberg Limits
ATD or date of measurement
UCT = Unconfined Compression Test
❑ Blank Casing PP = Pocket Penetrometer
ZZA
Zipper Zeman Associates., Inc
Geotechrilcal
BORING LOG
Figure A-2
Date Drilled: 06/22/2006
Logged By: JPG
and Environmental Consulting
APPENDIX B
LABORATORY TESTING PROCEDURES AND RESULTS
APPENDIX B
LABORATORY TESTING PROCEDURES AND RESULTS
81052440
' A series of laboratory tests were performed during the course of this study to
evaluate the index and geotechnical engineering properties of the subsurface soils.
Descriptions of the types of tests performed are given below.
' Visual Classification
Samples recovered from the exploration locations were visually classified in the
field during the exploration program. Representative portions of the samples were
carefully packaged in moisture tight containers and transported to our laboratory where
' the field classifications were verified or modified as required. Visual classification of soil
was generally done in accordance with the Unified Soil Classification system. Visual soil
classification includes evaluation of color, relative moisture content, soil type based upon
' grain size, and accessory soil types included in the sample. Soil classifications are
presented on the exploration logs in Appendix A.
Moisture Content Determination
Moisture content determinations were performed on representative samples
obtained from the exploration in order to aid in identification and correlation of soil
types. The determinations were made in general accordance with the test procedures
described in ASTM: D-2216. The results are shown on the exploration logs in Appendix
A.
U.S. Number 200 Wash
This test procedure determines the amount of material finer than a U.S. No. 200
sieve by washing. The determinations were made in general accordance with the test
procedures described in ASTM: D-1140. The results of the U.S. No. 200 wash
determinations for the samples were used in classification of the soils, and are presented
in this appendix.
Atterberg Limits
Atterberg limits are used primarily for classification and indexing of cohesive
soils. The liquid and plastic limits are two of the five Atterberg limits and are defined as
the moisture content of a cohesive soil at arbitrarily established limits for liquid and
plastic behavior, respectively. Liquid and plastic limits were established for selected
samples in general accordance with ASTM: D-423 and ASTM: D-424, respectively. The
results of the Atterberg limits are presented on a plasticity chart in this appendix where
the plasticity. index (liquid limit minus plastic limit) is related to the liquid limit. The
plastic limits and liquid limits are also presented adjacent to appropriate samples on the
exploration logs in Appendix A.
In -place Density
The in -place density of some site soils was determined by computing the volume
of a portion of the undisturbed samples from the boring explorations then weighing the
sample. The in -place densities computed is presented on the boring logs in Appendix A.
Unconfined Compression Test
In order to determine the undrained shear strength of a representative sample of
the cohesive soils encountered in the borings, an unconfined compression test was
conducted in general accordance with the ASTM: D-2166 test procedure. The test was
performed by trimming an undisturbed Shelby tube sample to a length of approximately 6
inches. Axial loading was then applied to the specimen (zero confining pressure) at a
constant rate of strain. The results of this test are presented in this appendix and on the
' appropriate boring log. The undrained shear strength of a cohesive soil is generally
considered equivalent to one-half its unconfined compressive strength.
Pocket Penetrometer
A calibrated hand device, a Pocket Penetrometer (PP), was utilized on relatively
undisturbed fine-grained soil samples. This device consists of a spring -loaded ram that is
forced into the soil sample by hand pressure and the amount of spring resistance required
for penetration provides an indication of the unconfined compressive strength. The
results of these tests are presented on the boring logs in Appendix A in tons per square
foot (tsf). The undrained shear strength of a cohesive soil is generally considered
equivalent to one-half its unconfined compressive strength.
U.S. N0.200 WASH TEST RESULTS
ASTM : D 1140
SAMPLE
LOCATION
DEPTH (ft)
MOISTURE
CONTENT (%)
PERCENT PASSING THE
U.S. NO. 200 SIEVE
B-1, S-3
16
23
37
B-1, S-7
35
14
2 i
B-2, S-9
27.5
31
54
ZZA PROJECT NO: 81052440 PROJECT NAME:
�+ ;�
Zipper Zeman Associates, Inc.
Geotechnical and Environmental Consulting TEST DATE: 02/21/2007 Johnson Residence
PLASTICITY CHART
ASTM D 4318
60
50
40
0
X
d
30
w
20
a
10
7
4
0
0 10 20 30 40 50 60 70 80 90 100
Liquid Limit %
• ..
• ..
Symbol
Boring
Sample
USCS
Description
Received
M.C. %
Liquid
Limit
Plastic
Limit.
Plasticity
Index
Comments
B-1 .
S-2
ML
35
40
27
12
silty CLAY of low plasticity .
B-1
S-5
ML .
32
37
27
10
silty CLAY of low plasticity
Remarks:
Zipper Zeman Associates Inc PROJECT NO: 81052440 PROJECT NAME:
Geotechnical and Environmental Consulting DATE OF TESTING: 02/21/2007 Johnson Residence
UNCONFINED COMPRESSION TEST
Project Johnson
Residence
Job No. J-81052440
Location of Project
Edmonds, WA
Description of Soil
Boring B-2. S-5
(Clayey SILT
with trace to some fine sand)
Tested By
JPG
Date of Testing 02/15/2007
Sample Data
Diameter 2.9 in
Area A U
6.47 in2 Height, L o 5.16 in
Volume 0.0193
ft3
Weight
2,28 lb Wet unit weight 118.1 pcf
Water content, w %
30
Dry unit wt.
90.8 pcf LRC = 1.761" (dial)+6.8645
Deformation
dial
reading
(x 10-3)
Load
dial
(units)
Sample
deformation
AL, in.
(col. 1 x 10-3)
Unit
strain
OL/LO
Area
CF
1 - e
Corrected
area, A',
sq in.
Total
load on
sample
(col. 2 x LRC)
Sample
unit
load, psi
1 1
2
3
4
5
6
7
8
20
7
0.020
0.0039
0.9961
6.49
19
2.96
40
10
0.040
0.0078
0.9922
6.52
24
3.76
60
13
0.060
0.0116
0.9884
6.54
30
4.55
80
16
0.080
0.0155
0.9845
6.57
35
5.34
100
20
0.100
0.0194
0.9806
6.59
42
6.38
120
24
0.120
0.0233
0.9767
6.62
49
7.42
140
28
0.140
0.0271
0.9729
6.65
56
8.45
160
31
0.160
0.0310
0.9690
6.67
61
9.21
180
35
0.180
0.0349
0.9651
6.70
68
10.22
200
38
0.200
0.0388
0.9612
6.73
74
10.97
220
41
0.220
0.0426
0.9574
6.75
79
11.71
240
43
0.240
0.0465
0.9535
6.78
83
12.18
260
46
0.260
0.0504
0.9496
6.81
88
12.90
280
49
0.280
0.0543
0.9457
6.84
93
13.62
300
51
0.300
0.0581
0.9419.
6.87
97
14.08
320
52
0.320
0.0620
0.9380
6.89
98
14.28
340
54
0.340
0.0659
0.9341
6.92
102
14.73
360
55
0.360
0.0698
0.9302
6.95
104
14.92
380
56
0.380
0.0736
0.9264
6.98
105
15.11
400
56
0.400
0.0775
0.9225
7.01
105
15.05
420
57
0.420
0.0814
0.9186
7.04
107
15.24
440
57
0.440
0.0853
0.9147
7.07
107
15.17
460
57
0.460
0.0891
0.9109
7.10
107
15.11
480
55
0.480
0.0930.
0.9070
7.13
104
14.55
500
54
0.500
1 0.0969
0.9031
7.16
1 102
1 14.24
520
53
0.520
0.1008
0.8992
7.19
100
13.93
540
51
0.540
0.1047
1 0.8953
7.22
97
13.39
Unconfined compressive strength q u = 15.24 psi
Cohesion = q ,/2 = 7.62 psi
ZIPPER ZEMAN ASSOCIATES, INC
PROJECT NO: J-81052440
PROJECT NAME:
GEOTECHNICAL AND ENVIRONMENTAL
DATE OF TESTING: 02/15/2007
Johnson Residence
CONSULTING
ZZA
Zipper Zeman Associates Inc.
Geotechnical and Environmental Consulting
A 1rerracon Company
Mr. Steve Johnson
16121 74th Place West
Edmonds, Washington 98026
Subject: Report of Geotechnical Services
Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
Edmonds, Washington
Dear Mr. Johnson:
81052440
March 29, 2007
RZCZJ VZ®
APR - 3 2009
BUlLDrNG DEP7;
Zipper Zeman Associates, Inc. (ZZA) is pleased to present herein a copy of the above -
referenced report. This report presents the results of our surface and subsurface exploration and
geotechnical engineering study relative to foundation and construction considerations for the
referenced project. Our services were completed in accordance with our Proposal for
Geotechnical Services (J-2440). dated April 5, 2006 and our Supplement to Agreement for
Services dated February 9, 2007.
The purpose of the study was to establish general surface and subsurface conditions at the
site from which conclusions and recommendations regarding foundation design and construction
considerations could be formulated. The scope of our services consisted of a literature review,
surficial reconnaissance, subsurface exploration, geotechnical engineering analysis, and
preparation of this report.
At the time this report was prepared, project plans were in the preliminary stage. As
such, we recommend that ZZA be allowed the opportunity to review the plans and specifications
for the project once they become available to determine that the recommendations presented
herein have been properly interpreted with respect to this project. This report is an instrument of
service and the conclusions presented herein are in respect to the subject property and have been
prepared in accordance with generally accepted geotechnical engineering practices. This report
has been prepared for the exclusive use of Mr. Steve Johnson, and other members of the project
team, for specific application to this project and the stated purpose.
SITE AND PROJECT DESCRIPTION
The subject property is located near the northeast corner of the intersection of 741h Place
West and 162° Street SW in Edmonds; Washington. The roughly rectangular shaped parcel is
approximately 5,005 square feet in size and is located within a moderately steep to steep west -
facing slope. The parcel is bounded to the west by 74th Place West and to the north, east, and
south by single-family residential development. Existing single-family structures are located
about 18 feet north and 16 feet east of the subject parcel.
STREET FILE
18905 33rd Avenue West #117, Lynnwood, WA 98036 425-771-3304 Fax: 425-771-3549
ZZA
Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
81052440
March 29, 2007
Page 2
Preliminary plans indicate that the residence will encompass the majority of the parcel.
We understand that "common area" associated with the Lorian Woods Plat is located along the
west, east, and south sides of the subject parcel and that Lot 10 is located immediately adjacent
to the northern lot line of the subject parcel. The plans indicate that the house will consist of
three floor levels stepped into the slope with lower, middle, and upper level finished floor
elevations of approximately 82.8 feet, 92 feet, and 101.2 feet, respectively. We understand that
the residence will be supported on conventional shallow spread foundations with subsurface
concrete walls. A combination of slab -on -grade concrete floors and wood framed floors over
crawl spaces is planned. The proposed building layout and existing site features are shown on
the enclosed Site and Exploration Plan, Figure 1.
The site is located within an area designated as the Meadowdale Landslide Hazard Area
by the City of Edmonds. Portions of the Meadowdale Landslide Hazard Area have reportedly
experienced historic slope instability. The Meadowdale Landslide Hazard Area and the subject
site meet the criteria established for Earth Subsidence and Landslide Hazard Areas presented in
Chapter 19.10 of the City of Edmonds Building Code. As such, permitting and development of
the site must meet the guidelines presented in Chapter 19.10 of the City of Edmonds Building
Code and the geotechnical report guidelines presented in. Chapter 19.10.030 of the City of
Edmonds Building Code.
REGIONAL GEOLOGY
We assessed the regional geology of the site and the surrounding vicinity by reviewing
the following regional publications and geotechnical reports.
• Washington Department of Natural Resources, Preliminary Surfzcial Geologic Map of
the Edmonds East and Edmonds West Quadrangles, Snohomish and King Counties,
Washington, Map GM-14, 1975.
• Roger Lowe Associates, Inc.; Final Report, Landslide Hazard Investigation,
Meadowdale Area, Edmonds, Washington; October 16, 1979.
• GeoEngineers Inc.; Report of Geotechnical Consultation, Property Value Appraisal and
Assessment, Meadowdale Landslide Area, Edmonds, Washington; February 28, 1985.
The project site is located on the western margin of the Intercity Plateau within the Puget
Lowland. The Puget Lowland is a north -south trending depression bounded on the east and west
by the Cascade and Olympic mountain ranges, respectively. The topography and geology of the
Puget Lowland and the Intercity Plateau are a direct result of several cycles of regional glaciation
during the Pleistocene epoch. The most recent cycle of glaciation, known as the Vashon Stade of
the Fraser Glaciation, ended approximately 13,500 years ago. The Vashon Stade is believed to
have covered the Puget Lowland with up to 3,000 to 5,000 feet of glacial ice in the deeper
portion of the Lowland.
The Preliminary Surficial Geologic Map of the Edmonds East and Edmonds West
' Quadrangles, Snohomish and King Counties, Washington describes the site and surrounding
vicinity as being mantled by Quaternary age "Old Landslide" deposits. The Old Landslide
' 81052440 Johnson Res Report 032907.doc
Proposed ZZA p sed Single -Family Residence
3 Lorian Woods Plat, Lot 9
81052440
' n j March 29, 2007
Page 3
' deposits are described as large slums that occurred during theablation
g p g anon (retreat) of the Puget
Lobe of the Vashon ice sheet by lowering of water table levels. The publication indicates that
' the landslides may have been active since original movement. This large landslide is locally
referred to as the Meadowdale Landslide Hazard Area and the Meadowdale Landslide Complex.
The geologic units mapped around the landslide suggest that the landslide occurred primarily
within Whidbey Formation deposits and may include deposits of the underlying Double Bluff
Drift.
The Whidbey Formation comprises pre-Vashon interglacial fluvial sediments. The
formation consists primarily of bedded sand, silt, and clay. Sorting is generally good within each
' individual bed. The upper portion of the unit is typically oxidized. Tectonically contorted
bedding is not uncommon. Due to clay beds within the Whidbey Formation, groundwater
percolating down through sandy zones tends to build up and move laterally on top of the clay
beds. Where these beds daylight. on hillsides and coastal bluffs, groundwater seepage and
landsliding are not uncommon.
The Double Bluff Drift comprises pre-Vashon glacial and non glacial deposits. The unit
contains fluvial gravels with variable silt and sand content, lodgment till, pebbly fine grained
glacial lacustrine silts, and massive deposits of silt and clay. The unit may show tectonic
deformation. The unit has a low permeability and hydraulic conductivity, and perched
groundwater often develops in the overlying Whidbey Formation, deposits, forming a weakened
zone in which the Whidbey Formation soils can slide.
' The site is located within the Meadowdale Landslide Hazard Area as defined by the City
of Edmonds and reported in the Roger Lowe Associates 1979 report. The report. describes the
' landslide mass as extending about 3,200 feet in a north -south direction along the shoreline of
Puget Sound and up to 650 feet in an easterly direction from the Burlington Northern railroad
right-of-way which is located near the toe of the landslide area. The topographic relief of the
' landslide area is about 150 feet, while the headscarp of the landslide extends up to about
elevation 300 feet. The landslide mass is reported to be on the order of 20 to 50 feet thick. The
initial movement of the landslide is believed to have occurred about 7,000 years ago as a result
' of rising sea levels associated with glacial retreat and shoreline erosion. Historic movement of
the landslide complex has primarily occurred within a zone approximately 400 feet wide
adjacent to and east of the Burlington Northern railroad right-of-way from the 1940's through the
' 1770's.
The evaluation completed by Roger Lowe Associates included a landslide hazard risk
' assessment and the development of a Landslide Hazard Map for the Meadowdale Landslide
Complex and surrounding vicinity. The 1979 Landslide Hazard Map suggests that the western
portion of the site is located within a 4A90 hazard area. This designation indicates a 90 percent
' probability of movement within an existing slump during a 25 year period. The eastern portion
of the site appears to be located within a 4A35 hazard area, indicates a 35 percent probability of
movement within an existing slump during a 25 year period. In the early 1980's, the City of
Edmonds implemented measures that contributed to lowering of groundwater levels within
portions of the Meadowdale landslide area. GeoEngineers reevaluated landslide hazards within
' 81052440 Johnson Res Report 032907.doc
' Pro i
ZZA Proposed p Single -Family Residence
Lorian Woods Plat, Lot 9
81052440
' March 29 2007 �AAAL Page 4
' the Meadowdale Landslide Complex to account for decreased
p groundwater levels and developed
a revised Landslide Hazard Map. The revised hazard map indicates that the western and eastern
' portions of the site have a 30 percent and 10 percent probability of movement within an existing
slump during a 25 year period, respectively.
' CITY OF EDMONDS LITERATURE REVIEW
' In addition to our review of the Roger Lowe Associates and GeoEngineers reports
completed for the City of Edmonds, we completed a review of documents on file with the City of
Edmonds relative to landsliding, ground subsidence, erosion, and other geotechnical related
' problems within an approximate 400 foot radius of the subject site. Specifically, our review
included the following documents.
I. Associated Earth Sciences, Inc.; Limited Slope Reconnaissance, 16202 — 72"d Avenue
West, Edmonds, Washington; March 15, 2001.
2. City of Edmonds; RE: Slope Investigation, Johnson Residence, 16121 — 74`h Place West,
Edmonds, Washington; March 23, 2001.
3. Landau Associates; Slope Stability Consultation, 16202 — 72"d Avenue West, Edmonds,
Washington; April 19, 2001.
4. City of Edmonds; RE:'Slope Stability Consultation, 16202 — 72"d Avenue West, Edmonds,
Washington; April 26, 2001.
5. Landau Associates; Landslide Evaluation Meadowdale Area — Lorian Woods/Sequoia
Ridge Plats, Edmonds, Washington; September 25 2003.
6. City of Edmonds; RE: Localized landslide near Lorian Woods/Sequoia Ridge Plats,
Edmonds, Edmonds, Washington; September 25, 2003.
7. Terra Associates, Inc.; Geotechnical Consultation, Deck Repair, Johnson Residence,
Lorian Woods, Lot 8, Edmonds, Washington; February 27, 2003.
8. Terra Associates, Inc.; Final Letter, Earthwork Observation and Testing, Johnson
Residence, Lorian Woods, Lot 8, Edmonds, Washington; June 13, 2003.
Documents 1 through 4 are associated with a landslide that occurred on September 13,
1998 and appeared to reactivate in February 2001. The landslide(s) appear to have occurred
about 350 to 400 feet southeast of the subject property on a steep west -facing slope located west
of 16202 72nd Avenue West. The slope was reported to have an inclination of about 1H:1V and
a total relief of about 120 feet. The slide was reportedly shallow in nature, consisted of a rapidly
moving mud and debris, and extended from the toe to the top of the slope. The risk of future
landsliding adversely affecting the properties immediately above and below the steep slope was
considered high.
Documents 5 and 6 are associated with a landslide that occurred on or around September
' 15, 2003. The landslide reportedly occurred about 400 feet northeast of the subject property
between Lot 2 of Lorian Woods and Lot 4 of the Sequoia Ridge Plat. The slide reportedly
consisted of a combination block slide and mudflow that extended to a depth of about 3 to 5 feet
' (measured perpendicular to the slope face) and occurred on the face of a steep landslide scarp.
1
81052440 Johnson Res Report 032907.doc
1
1
Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
81052440
March 29, 2007
Page 5
Ground cracks were observed up gradient (east of the landslide) and the documents indicate an
increased risk to properties immediately above and below the slide area.
Documents 7 and 8 appear to be associated with settlement damage to a small concrete
patio slab and two patio columns located near the southwest corner of the residence located on
Lot 8 of Lorian Woods, about 15 feet east of the subject site. Settlement damage reportedly
occurred due to consolidation of fill soils. The documents indicate that the slab was removed
and replaced above a compacted subgrade and that the two columns were supported on driven 2-
inch diameter pipe piles.
SITE CONDITIONS
We completed a visual reconnaissance and subsurface exploration of the site in June
2006. The surface and subsurface conditions are described below. Pertinent site features and
approximate exploration locations for the proposed development area are shown on the Site and
Exploration Plan, Figure 1. Details of the field exploration procedures along with the
exploration logs are presented in Appendix A.
Surface Conditions
The subject parcel consists of a moderately steep to steep west -facing slope with
inclinations ranging from about 28 to 40 percent and a total relief of about 20 feet. A steep west -
facing slope with inclinations ranging from about 45 to 55 percent and a total relief of about 6 to
7 feet is present within the "common area" located between the subject parcel and the 741h Place
West right-of-way. This steeper slope area appears to be the result of cuts associated with
roadway and utility construction.
The parcel is predominantly vegetated with grass and includes some shrubs and
ornamental plantings within the northern portion of the lot. We did not observe any obvious
indications of recent slope movement, such as ground cracks or hummocky topography at the
time of our evaluation. We did not observe any standing or flowing surface water or indications
of groundwater seepage within the proposed development area at the time of our evaluation.
The base of a steep west -facing slope is located about 150 to 180 feet east of the subject
parcel near the eastern side of Lot 8. The slope exhibited geomorphic indications of surficial soil
creep and shallow surficial landsliding. Based on our observations and published geologic maps
and geotechnical reports of the area, this steep slope is interpreted as a portion of the
Meadowdale landslide headscarp.
Subsurface Conditions
The subsurface exploration completed for this study consisted of two hollow stem auger
borings within the proposed building footprint. Boring B-1 was advanced near the western side
of the proposed residence and was completed to a depth of approximately 56.5 feet below the
ground surface. Boring B-2 was advanced near the eastern side of the proposed residence and
81052440 Johnson Res Report 032907.doc
rKt
Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
81052440
March 29, 2007
Page 6
was completed to a depth of approximately 51.5 feet below the ground surface. The approximate
exploration locations are shown on the Site and Exploration Plan, Figure 1. Figure 2 presents a
generalized subsurface profile depicting conditions down the fall line of the west -facing slope.
In general, the explorations disclosed approximately 36 to 45 feet of colluvial deposits
underlain by undisturbed native soils interpreted as Whidbey Formation deposits. The colluvial
soils generally consisted of loose to medium dense sand with variable silt content and medium
stiff to stiff, silty clay and clayey silt with variable sand content. The fine grained portions of the
colluvium exhibited a disturbed, blocky texture with inclusions of hard silt and portions of the
granular deposits exhibited a lack of depositional structure. The underlying Whidbey deposits
generally consisted of very stiff to hard, moist, massive to finely laminated clayey silt and
extended to the maximum depth explored at 56.5 feet below the ground surface. The subsurface
soils disclosed in our explorations were generally consistent with the published geologic units for
the site vicinity.
Groundwater
Groundwater was observed in borings B-1 and B-2 at the time of our evaluation. The
observed groundwater was interpreted to represent a perched condition above the low
permeability, undisturbed Whidbey Formation deposits encountered below the colluvium.
Monitoring wells were installed in borings B-1 and B-2 to record fluctuations in the groundwater
conditions. Groundwater levels recorded at the time of drilling and during subsequent
monitoring well soundings are presented in the table below.
GROUNDWATER CONDITIONS
Exploration
Number
Date Measured
Groundwater Depth Below
Ground "Surface ft
Groundwater Elevation (ft)
06/22/2006 *
15.5
75
B-1
10/09/2006
12.6
77.9
11 / 16/2006
11.4
79.1
06/22/2006 *
13.5
89.5
B-2
10/09/2006
20.3
82.7
11 / 16/2006
19.3
83.7
* Groundwater level estimates developed at the time of drilling.
Groundwater conditions should be expected to fluctuate due to changes in season,
precipitation patterns, site utilization, on -site or off -site irrigation activities, and other on- and
off -site factors.
81052440 Johnson Res Report 032907.doc
1
1
1
Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
81052440
March 29, 2007
Page 7
CONCLUSIONS AND RECOMMENDATIONS
General
We understand that the residence will consist of three levels stepped into the slope with
lower, middle, and upper level finished floor elevations of approximately 82.8 feet, 92 feet, and
101.2 feet, respectively. We understand that the residence will be supported on conventional
shallow spread foundations with subsurface concrete retaining walls. A combination of slab -on -
grade concrete floors and wood framed floors over crawl spaces are planned.
Preliminary plans indicate that the residence will encompass the majority of the parcel.
Based on the subsurface conditions disclosed at the exploration locations, the project appears
geotechnically feasible utilizing conventional shallow foundation support and slab -on -grade
concrete floors or wood framed floors over crawl spaces. However, the site is mapped within a
portion of the Meadowdale Landslide area having a 10 to 30 percent probability of movement in
a 25 year period. Given the lateral extent, depth, and topographic relief of the Meadowdale
Landslide, it is our opinion that mitigation of this risk of movement is not feasible. Our analyses
also indicate that portions of the site soils are susceptible to liquefaction and settlement during a
design seismic event. Given the proximity of the residence to the property lines, the planned cut
depths, and the recommended maximum temporary cut slope inclination of 1.5H:1 V, we
anticipate that temporary shoring will likely be necessary.
Specific recommendations for project design, including a more detail discussion
regarding the above concerns, are presented in the following sections.
Seismic Considerations
Tectonic Setting
' The tectonic setting of western Washington is dominated by the Cascadia Subduction
Zone formed by the Juan de Fuca plate subducting beneath the North American Plate. This
setting leads to intraplate, crustal, and interplate earthquake sources. Seismic hazards relate to
risks of injury to people and damage to property resulting from these three principle earthquake
sources.
Soil Liquefaction
Liquefaction is a phenomenon wherein saturated cohesionless soils build up excess pore
' water pressures during earthquake loading. Liquefaction typically occurs in loose soils, but may
occur in denser soils if the ground shaking is sufficiently strong. We assessed the potential for
liquefaction using the simplified procedure originally developed by Seed and Idriss (1971), and
' updated by Idriss (2004). It is an empirical method based on surficial expressions of soil
liquefaction during past earthquakes. The method involves a comparison of earthquake -induced
stresses to soil strength at the location and depth of each exploration sample. Soil strength is
' correlated to the standard penetration resistance blow count, (Nl)60, after it has been normalized
to an effective overburden pressure of 1 ton per square foot and corrected for drilling/sampling
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procedures and fines content. Earthquake -induced stresses are estimated with an equation that
includes horizontal Peak Ground Acceleration (PGA) at the ground surface and earthquake
magnitude as variables.
Our analysis was completed for a magnitude 7 design earthquake with a 2,500-year return
period, and used a PGA of 0.34g. This PGA value is based on USGS National Seismic Hazard
Mapping Project 1996 spectral ordinates and has been factored in accordance with the 2003
International Building Code (IBC) seismic design method. The USGS obtained these values by
performing probabilistic seismic hazard analyses that considered all potential earthquake sources
that may contribute to strong ground shaking at the site. Magnitude, distance, and probability of
occurrence were all factored into this hazard analysis.
Based on our analyses, zones of liquefied soil are anticipated to develop within the
granular portions of the site colluvial deposits during ground shaking from an event with a 2,500-
year return period. Based on the conditions encountered in borings B-1 and B-2, it appears that
potentially liquefiable zones are laterally and vertically discontinuous due to the disturbed nature
' of the colluvial deposits. Soil liquefaction may be expressed at the ground surface as sand boils,
ground cracks, vertical settlements, and lateral displacements. However, given the discontinuous
nature of the potentially liquefiable zones and the presence of non -liquefiable clayey soils
' located above the perched water table, surficial expression of soil liquefaction such as sand boils
and ground cracking may not be observed at the project site.
' Ground shaking from an earthquake can result in subsidence of the ground surface and
settlement of on -grade supported facilities. Seismic induced settlements tend to be greatest in
loose granular soils, and particularly soils which are susceptible to liquefaction. Based on the
' results of our analyses, we estimate that total vertical settlements on the order of 1 to 2 inches
could be experienced at the site during a design earthquake. Differential settlement could
approach %2 to 1 inch over a distance of about 30 feet.
' International Building Code Seismic Design Parameters
It is our understanding that seismic design for this project will be completed in
accordance with the procedures presented in the 2003 IBC. Per the 2003 IBC seismic design
procedures, the presence of liquefiable soils requires a Site Class definition of F. A Site Class of
' F requires a site -specific dynamic site response analysis, except for structures with periods of
vibration equal to or less than 0.5 seconds. For structures with periods of vibration equal to or
less than 0.5 seconds, site coefficients Fa and F,, may be taken equal to the values for the Site
' Class determined without regard to liquefaction. The structure is expected to have. a period less
than 0.5 seconds. Based on the subsurface conditions encountered at the site and published
geologic literature, it is our opinion that an IBC Site Class of D describes the average properties
of soil beneath the site to a depth of 100 feet, when disregarding liquefaction. This designation
describes soils that are considered stiff with a shear wave velocity between 600 and 1,200 feet
per second, average Standard Penetration Test values between 15 and 50, and an undrained shear
' strength between 1,000 and 2,000 psf.
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The USGS National Seismic Hazard Mapping Project computes the 1996 spectral
ordinates (5 percent damping) at building periods of 0.2 and 1.0 seconds for ground motions at
the project site with a 2 percent probability of exceedance in 50 years (2,500-year return period)
as 1.28g and 0.45g. Therefore, we recommend that Ss and Si be assigned values of 1.28g and
0.45g, respectively.
Environmental Critical Area Considerations
The site is located within a documented landslide area designated as the Meadowdale
Landslide Hazard Area by the City of Edmonds. The extent and nature of this landslide area are
described in the Final Report, Landslide Hazard Investigation, Meadowdale Area, Edmonds,
Washington prepared by Roger Lowe Associates, 1979 and the Report of Geotechnical
Consultation, Property Value Appraisal and Assessment, Meadowdale Landslide Area,
Edmonds, Washington, prepared by GeoEngineers, 1985.
The evaluation completed by Roger Lowe Associates included a landslide hazard risk
assessment and the development of a Landslide Hazard Map for the Meadowdale Landslide
Hazard Area and surrounding vicinity. In the early 1980's, the City of.Edmonds implemented
measures that contributed to lowering of groundwater levels within portions of the Meadowdale
landslide area. GeoEngineers reevaluated landslide hazards within the Meadowdale Landslide
Complex to account for decreased groundwater levels and developed a revised Landslide Hazard
Map. The revised hazard map indicates that the western and eastern portions of the subject site
have a 30 percent and 10 percent probability of movement within an existing laterally extensive
slump during a 25 year period, respectively.
Due to the site location within the Meadowdale Landslide Hazard Area and the site
specific geotechnical and topographic conditions, the site appears to meet the criteria for an
Earth Subsidence and Landslide Hazard Area based on the Edmonds Community Development
Codes. This designation generally applies when a site is located within mapped areas of historic
landsliding or areas with slope inclinations greater than 15 percent, in combination with certain
adverse hydrogeologic conditions. For sites with this designation, the City of Edmonds requires
a site -specific geotechnical evaluation addressing the risk associated with the landslide hazard
area and providing specific recommendations concerning the development of the site in
accordance with the City of Edmonds geotechnical report requirements. The conclusions and
recommendations presented in this report are intended to address the concerns related to the
landslide hazard designation in general accordance with the Chapter 19.10 of the City of
Edmonds Building Code
Provided that the recommendations presented in this report are implemented, the
proposed development is considered geotechnically feasible and is not anticipated to adversely
affect the stability of the site, the adjacent properties, or the surrounding area. It is our opinion
that the subject site will remain stable following development, as defined in Chapter 19.10.020-B
of the City of Edmonds Building Code, which defines stable to mean "that the risk of damage to
the proposed development, or to adjacent properties, from soil instability shall be minimal and
that the proposed development will not increase the potential for soil movement." It should be
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' understood that the site is mapped within a portion of the Meadowdale Landslide area having a
10 to 30 percent probability of movement in a 25 year period. Given the lateral extent, depth,
' and topographic relief of the Meadowdale Landslide, it is our opinion that mitigation of this risk
of movement is not feasible. Chapter 19.10.020-B of the City of Edmonds Building Code
indicates that such a hazard shall not render a site proposed for single-family residences to be
' presumed unstable for the purposes of this provision if the risk of probability of earth movement
is measured at 30 percent or less within a 25 year period.
' Slope Stability Considerations
ZZA completed slope stability analyses for the site using the XSTABL5.2 computer
' program. The stability analyses were based on a generalized subsurface profile taken down the
fall of the slope as shown on Figure 2. The soil profile consists of colluvium deposits over
' undisturbed Whidbey Formation deposits. Groundwater was modeled based on site specific
piezometric measurements completed during the winter of 2006.
' Static and pseudo -static (seismic) stability analyses were completed for three surface
profiles. These profiles are outlined below and presented on Figures 3 through 7.
' • Figure 3 — Depicts the current configuration and stability of the slope for static
conditions.
• Figure 4 — Depicts the current configuration and stability of the slope for pseudo -static
conditions.
• Figure 5 — Depicts the configuration of the slope during construction for static conditions.
The profile and analysis includes the use of two temporary ecology block shoring walls,
' as discussed in the Temporary Shoring section of this report.
• Figure 6 — Depicts the configuration of the slope after construction for static conditions.
• Figure 7 — Depicts the configuration of the slope after construction pseudo -static
conditions.
Our analyses of the current and post construction slope configurations were completed
' for static and pseudo -static conditions. Our analyses used a pseudo -static coefficient (kh) of 0.17,
or % of Amax calculated in accordance with the procedures presented in the 2003 International
Building Code. Friction angles and cohesion values used in our analyses for each soil stratum
are presented on Figures 3 through 7. Based on the site specific boring data, it is our opinion that
the referenced friction angle and cohesion values are reasonable estimates of the site soil strength
parameters.
' Factors of safetyf o 1.5 or greater under static conditions and 1.1 or greater under pseudo -
static conditions are generally considered acceptable for permanent structures and slopes. Static
safety factors of 1.1 or greater are generally considered acceptable for temporary structures and
slopes. Our analysis of the current slope configuration indicates static and pseudo -static safety
' factors of about 2.2 and 1.1, respectively. Our analysis of the slope configuration during
construction indicates a static safety factor of about 1.6. Our analysis of the slope configuration
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' after construction indicates static
and under pseudo -static safety factors of about 2.0 and 1.1,
respectively.
' It should be noted that the slope stability analyses described above are associated only
' with the subject site. These analyses and reported safety factors are not intended to represent
that stability of the larger scale Meadowdale Landslide mass. We evaluated the stability of the
larger scale Meadowdale Landslide mass by reviewing the 1979 Landslide Hazard Investigation
' prepared by Roger Lowe Associates and the revised Landslide Hazard Map for the Meadowdale
Landslide Area prepared by Geoengineers in 1985. These publications indicate that the western
and eastern portions of the subject site have a 30 percent and 10 percent probability of movement
' 'within an existing extensive slump during a 25 year period, respectively. Based on our site
specific subsurface explorations and our reconnaissance of the surrounding vicinity, it is our
opinion that the site conditions generally appear to be consistent with the conditions reported for
' the mapped risk probabilities.
The landslide mechanisms modeled in our site specific slope stability analyses and the
' mechanism indicated for the project vicinity in the Roger Lowe Associates and GeoEngineers
reports primarily consist of rotational/slump failures and deep seated rotational or complex
landslides. Our evaluation also considered other types of earth movement including debris
' avalanches, earth flows, debris falls, and mud flows.
Our evaluation indicates that the base of a steep west -facing slope is located about 150 to
' 180 feet east of the subject parcel near the eastern side of Lot 8. This steep slope exhibited
geomorphic indications of surficial soil creep and shallow surficial landsliding. Based on our
observations and published geologic maps and geotechnical reports of the area, this steep slope is
' interpreted as a portion of the Meadowdale landslide headscarp. Based on our review of City
files, portions of the headscarp appear to be susceptible to rapid moving earth topples and slides,
and mud and debris flows. However, given the distance of the subject site from the base of the
' slope and the relatively level ground surface of Lot 8, which would tend to act as a run -out area
and reduce the velocity of mass wasting material, it is our opinion that the risk of damage to the
subject site from landslide debris derived from the steep west -facing headscarp is low.
Site Preparation
' We anticipate that this project will require cuts ranging from about 5 feet near the west
and east sides of the site to about 13 feet near the middle of the site. Site preparation should
include the removal of all vegetation, root mass, organic soils, existing structures, undocumented
' fill material, and any deleterious debris from building and paving areas, or those locations where
"structural fill" is to be placed.
' Preparation for site grading and construction should begin with procedures intended to
drain ponded water and control surface water runoff. It will be difficult to successfully utilize
on -site soils as "structural fill" if accumulated water is not drained prior to grading, or if drainage
' is not controlled during construction. Attempting to grade the site without adequate drainage
control measures will reduce the amount of on -site soil effectively available for use, increase the
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amount of select import fill materials required, and ultimately increase the cost of the earthwork
and foundation construction phases of the project.
Following clearing and grubbing, any organic -rich topsoil will need to be stripped in the
building and pavement areas, as well as those areas to receive structural fill. Based on our
explorations, topsoil (grass sod) on the order of 3 inches thick appears to mantle the site. The
topsoil should be removed and should not be reused as structural fill. Localized areas of deeper
organics, such as root systems, may be encountered within the project site and should likewise be
removed. Any excavations that extend below finish grades should be backfilled with structural
fill as outlined subsequently in this report.
After stripping of topsoil and excavation to design grade is completed, the exposed soils
will generally consist of silty clay to clayey silt with variable sand content. Prior to placement of
structural fill, we recommend that foundation, floor subgrade, pavement areas, and other areas to
receive structural fill be proofrolled and compacted to a firm and unyielding condition in order to
achieve a minimum compaction level of 95 percent of the modified Proctor maximum dry
density as determined by the ASTM:D-1557 test procedure. Due to the silty nature of the
exposed soils, proofrolling and adequate compaction can only be achieved when the soils are
within approximately f 2 percent of the optimum moisture content. Soils which appear firm after
stripping may be proof -rolled with a heavy compactor, loaded double -axle dump truck, or other
heavy equipment under the observation of a qualified geotechnical engineer, or his
representative. This observer will assess the subgrade conditions prior to filling. Areas where
loose surface soils exist due to grubbing and stripping operations should be considered fill to the
depth of the disturbance and treated as subsequently recommended for structural fill placement.
The need for or advisability of proofrolling due to soil moisture conditions should determined at
the time of construction. We recommend that a representative of our firm observe the soil
conditions prior to and during proofrolling to evaluate the suitability of stripped subgrades prior
to fill placement.
Earthwork may be difficult or impossible during periods of elevated soil moisture and
wet weather due to the moisture sensitive nature of the silty and clayey site soils. Excavated site
soils may not be reusable as structural fill depending on the moisture content and weather
conditions at the time of construction. If soils are stockpiled for future reuse and wet weather is
anticipated, the stockpile should be protected with plastic sheeting that is securely anchored. If
on -site soils become unusable, it may become necessary to import clean, granular soils to
complete wet weather site work.
Subgrade soils that become disturbed due to elevated moisture conditions should be
overexcavated to expose firm, non -yielding, non -organic soils and backfilled with compacted
structural fill. We recommend that the earthwork portion of this project be completed during
' extended periods of dry weather if possible. If earthwork is completed during the wet season
(typically November through May) it may be necessary to take extra precautionary measures to
protect subgrade soils. Wet season earthwork may require additional mitigative measures
' beyond that which would be expected during the drier summer and fall months. This could
include diversion of surface runoff around exposed soils, draining of ponded water on the site,
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and collection and rerouting of groundwater seepage from upgradient on- and off -
site sources.
Once subgrades are established, it may be necessary to protect the exposed subgrade soils from
' construction traffic. Placing quarry spalls, crushed recycled concrete, or clean pit -run sand and
gravel over these areas would further protect the soils from construction traffic.
' Structural Fill
All fill material placed in building, pavement, and non -landscaped areas should be placed
in accordance with the recommendations herein for structural fill. Prior to placement, the
surfaces to receive structural fill should be prepared as previously described. All structural fill
should be free of organic material, debris, or other deleterious material. Individual particle size
should be less than 3 inches in maximum dimension.
Structural fill should be placed in lifts no greater than 8 inches in loose thickness. The
structural fill should be compacted to at least 95 percent of the modified Proctor. maximum dry
density as determined by the ASTM:D-1557 test procedure in building areas and to a depth of 2
feet below the subgrade surface in pavement areas. Below a depth of 2 feet in pavement areas,
the structural fill should be compacted to at least 90 percent of ASTM:D-1557. We recommend
that a representative from our firm be present during grading so that an adequate number of
density tests can be conducted as structural fill placement occurs. In this way, the adequacy of
the earthwork may be evaluated as it proceeds. In the case of roadway and utility trench filling
in municipal rights -of -way, the backfill should be placed and compacted in accordance with
current local codes and standards.
The suitability of soils for structural fill use depends primarily on the gradation and
moisture content of the soil when it is placed. As the amount of fines (that soil fraction passing
the U.S. No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in
moisture content and adequate compaction becomes more difficult, or impossible, to achieve.
Generally, soils containing more than about 5 percent fines by weight (based on that soil fraction
passing the U.S. No. 4 sieve) cannot be compacted to a firm, non -yielding condition when the
moisture content is more than a few percent from optimum. The optimum moisture content is
that which yields the greatest soil density under a given compactive effort.
At the time of the subsurface evaluation, the site soils disclosed by the explorations
appeared to have moisture contents above their estimated optimum moisture content relative to
their possible use as structural fill. Due to the high moisture sensitivity of the site soils, we
anticipate that adequate moisture control and compaction of these silty and clayey soils will be
difficult or impossible to achieve even under favorable weather conditions. We recommend that
the project include provisions for the export of on site cut soils and import of "clean" free
draining sand and gravel, as discussed below.
We recommend that import fill consisting of a "clean", free -draining pit -run sand and
gravel be used. Such material should generally contain less than 5 percent fines, based on that
soil fraction passing the U.S. No. 4 sieve, and not contain discrete particles greater than 3 inches
in maximum dimension. It should be noted that the placement of structural fill is, in many cases,
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weather -dependent. Delays due to inclement weather are common even when using select
granular fill. We recommend that site grading and earthwork be scheduled for the drier months,
if at all possible.
Temporary Cut Slopes
We anticipate that temporary open cuts may be utilized during the construction of foundation
elements for the proposed structure. Temporary slope stability is a function of many factors,
including the following:
'
1. The presence and abundance of groundwater;
2. The type and density of the various soil strata;
3. 'The depth of cut;
4. Surcharge loading adjacent to the excavation; and
5. The length
of time the excavation remains open.
' It is exceedingly difficult under the variable circumstances to pre -establish a safe and
"maintenance -free" temporary cut slope angle. Therefore, it should be the responsibility of the
contractor to maintain safe slope configurations since the contractor is continuously at the job
' site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface
materials and groundwater conditions encountered. It may be necessary to drape temporary
slopes with plastic or to otherwise protect the slopes from the elements and minimize sloughing
' and erosion. We do not recommend vertical slopes or cuts deeper than 4 feet if worker access is
necessary. The cuts should be adequately sloped or supported to prevent injury to personnel
from local sloughing and spalling. The excavation should conform to applicable Federal, State,
and local regulations.
According to Chapter 296-155, Part N, Excavation Trenching and Shoring, of the
' Washington Administrative Code (WAC), it is our opinion that the existing colluvial soils
encountered at the site within the planned cut depths are representative of a WAC Type C soil.
According to the Code, excavations less than 20 feet deep in Type C soils may be cut at a
maximum temporary slope angle of 34 degrees (1 %2H:1 V).
Zones of perched groundwater may be encountered during site excavation. This
' condition may require the use of flatter temporary slopes or the use of additional temporary
shoring. Alternatively, it may be feasible to allow the area(s) to drain prior to continuing the
excavation.
' The stability of temporary slopes is affected by the length of time the excavation remains
open. The design and construction schedule should make every effort to minimize the time
' excavations remain open. It may be necessary to backfill temporary cut slopes if the project
experiences protracted delays.
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' Temporary Shoring
p Y g
' Based on our review of the preliminary project plans, the WAC temporary cut slope
inclination of I V2H:IV, and our slope stability analyses, it appears that temporary shoring will be
' required for portions of the north, south, and eastern sides of the lower level, and along the
eastern property line. Several temporary shoring options have been considered for this project
including cantilever soldier pile walls, cantilever sheet. pile walls, and gravity walls such as
concrete ecology block and Ultra Block walls. We understand that ecology block walls are the
preferred type of temporary shoring wall. Based on the subsurface conditions encountered in our
explorations, we recommend that a maximum wall height of 6 feet and a wall batter of 1H:6V be
' used for planning purposes. Based on our slope stability analyses, we recommend that the
project plans include 6 foot high temporary ecology block walls behind the northern, southern,
and eastern lower level subgrade walls and along the eastern property line.
' We anticipate that it will be extremely difficult to remove these temporary shoring walls
once permanent cast -in -place concrete walls are constructed. We recommend that the project
' plans and budget include provisions for abandoning the ecology walls in place behind the
permanent cast -in -place walls. ZZA is available to provide additional geotechnical engineering
recommendations and/or design services for temporary ecology block gravity shoring systems.
Permanent Slopes
' Permanent cut and fill slopes should be constructed no steeper than 2H:IV, provided that
all embankment fill is compacted to at least 90 percent of the modified Proctor maximum dry
density as determined by the ASTM:D-1557 test procedure. It has been our experience that
' permanent slopes steeper than 2H:1 V will tend to ravel and slough to a flatter inclination over
time. In addition, with steeper slopes, topsoil erodes readily and it is more difficult and takes
longer to establish vegetation for slope protection.
' All permanent slopes should be provided with deep-rooted ground cover immediately
after they are completed. If the time of year does not allow the growth of stabilizing vegetation,
finished slopes should be provided with temporary erosion protection. Temporary erosion
protection could include the use of anchored sheet plastic or rolled erosion protection material,
such as Jute matting or Curlex II, if vegetation has not been established by the regional wet
' season (typically November through May).
Foundation Considerations
' We understand that the preliminary design included the use of conventional shallow
spread foundations. In our opinion, conventional spread footings will provide adequate support
for the planned structure, provided that the subgrade is prepared in accordance with the
recommendations presented below and that the potential for liquefaction induced settlement is
considered acceptable.
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' As discussed in the Seismic Considerations section of this report, we estimate that total
liquefaction induced settlements on the order of 1 to 2 inches could be experienced at the site
' during a design earthquake. Differential seismic induced settlements could approach %2 to 1 inch
over a distance of about 30 feet. If the risk of seismic induced settlement is not considered
acceptable, we recommend that the house be supported on piles. ZZA is available to provide
' design recommendations for pile foundations, if needed.
Based on our subsurface explorations, we anticipate that shallow foundations will be
underlain by about 30 feet of colluvial soils primarily consisting of medium stiff, silty clay with
variable sand content and loose to medium dense sand with variable silt content. To reduce total
' and differential static settlements to tolerable levels and provide a firm subgrade, we recommend
that the upper 18 .inches of the foundation subgrade be compacted to a firm and unyielding
condition and to at least 95 percent of the modified Proctor maximum dry density as determined
' by the ASTM:D-1557 test procedure. If soil moisture conditions will not allow for this level of
compaction, the subgrade soils should be removed to a depth of 18 inches below the bottom of
the foundation and replaced with structural fill compacted to a firm and non yielding condition
' and to at least 95 percent of the modified Proctor maximum dry density. The overexcavation
should extend laterally beyond the edge of the footing a distance equal to the depth of the
overexcavation.
Continuous or isolated column footings founded as described above may be designed for
a maximum allowable bearing pressure of 2,000 psf. A one-third increase in this bearing
' pressure may be used for short-term wind or seismic loading. For building and retaining wall
foundations, we recommend using an allowable base friction value of 0.35 and a maximum
allowable passive resistance of 230 pcf. The allowable base friction and passive resistance
1 values include a safety factor of 1.5. Exterior footings should extend at least 18 inches below
adjacent grade for frost protection, while the interior footings should extend at least 12 inches
below adjacent grade. We recommend that all continuous and isolated footings be at least 16 and
18 inches in width, respectively.
We estimate that the total static settlement of foundation members supported as
' recommended above may approach I inch. Static differential settlement of foundations could
approach %2 inch over a distance of 30 feet. Settlements would occur elastically as the loads are
applied. As previously discussed in the Seismic Considerations section of this report,
foundations may be subject to total seismic settlements on the order of 1 to 2 inches. Seismic
differential settlement of foundations could approach 'h to l .inch over a distance of 30 feet. We
recommend that the structural engineer include provisions in the foundation design to minimize
' the adverse effects of potential seismic induced differential settlement.
Foundation settlement is oftentimes a function of the condition of the footing excavation
' subgrade. Footing excavations should be free of loose or soft soil, slough, debris, or water prior
to pouring footing concrete.
' The moisture sensitive nature of the on -site soils may require that the footing excavations
be covered with a lift of crushed rock or a lean concrete "mud mat" to minimize disturbance of
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the bearing surface during construction in wet weather. Under no circulnstances should footings
be cast atop loose or soft soil, slough, debris, or surfaces with standing water. We recommend
that a representative from our firm observe the condition of the footing subgrades prior to the
pouring of concrete, or a lean concrete mud mat, in order to confirm that the bearing soils are
undisturbed and that conditions are consistent with the recommendations contained within this
report.
BackfiRed Walls
Preliminary plans indicate that the residence will be constructed in close proximity to the
' property lines and that temporary open cuts and shoring will be required to complete the planned
excavations for the structure. In order to reduce the distance that project excavations extend into
the slope and the height of the resulting cut slopes and shoring walls, we recommend that the
subgrade walls (particularly the north, south, and eastern walls for the lower level) be designed
in a manner that will minimize the length of the "heel", or that portion of the wall footing that
extends toward to slope.
' As discussed in the Temporary Cut Slope section of this report, the stability of temporary
cuts is affected by the length of time the cut remains open. To reduce the length of time
' temporary cuts remain open, we recommend that backfilled walls for the structure be designed in
a manner that will allow for the placement of wall backfill before the placement of structural
framing and floors, or that the design include provisions for temporary bracing. Further, we
' recommend that the structural engineer specify a minimum concrete cure time or minimum
concrete unconfined compressive strength that should be attained before subgrade walls are
backfilled.
All backfill placed behind walls or around foundation elements should be placed in
accordance with our recommendations for structural fill. The following recommended earth
pressures, presented as equivalent fluid weights, are based on the assumption of a level backfill
surface and no buildup of hydrostatic pressure behind the wall. To minimize lateral earth
pressures and prevent the buildup of hydrostatic pressures, the backfill within 24 inches of the
' wall should contain less than 5 percent fines, based on that portion passing the U.S. No. 4 sieve,
coupled with a perforated pipe drain placed at the base of the wall backfill, similar in
configuration to that described for the perimeter footings. We anticipate that the lower level of
' the structure may experience moderate groundwater seepage. We recommend that 6-inch
diameter drain pipes be used for the lower level of the structure. The wall drain system should
include permanent cleanouts to allow for potential future maintenance of the system. The upper
' 1-foot of the wall backfill should consist of a low permeability silty soil and be sloped away
from the wall in order to reduce the potential for surface water infiltration behind the wall.
' If the backfilled walls are structurally restrained from lateral movement at the top, we
recommend that they be designed for an "at -rest" equivalent fluid weight of 55 pounds per cubic
foot (pcf). If the top of the wall is free to move laterally in an amount equal to at least 0.1
percent of the wall height during placement of backfill soils, they may be designed for an
"active" equivalent fluid weight of 35 pcf.
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We recommend uniform seismic surcharges equivalent to 7H in pounds per square foot
(rectangular distribution) for yielding walls and I I for walls structurally restrained from lateral
movement, where H is the height of the wall above finished grade in feet.
Surcharges due to sloping ground, adjacent footings, vehicles, construction equipment,
etc., must be added to these values. The above equivalent fluid pressures assume that the
' backfill is compacted to approximately 90 to 92 percent of the modified Proctor maximum dry
density determined in accordance with ASTM:D-1557. Additional compaction adjacent to the
wall will increase the earth pressure, while a lesser degree of compaction could result in post
construction settlements.
Slab -On -Grade Floors
' In our opinion, the use of slab -on -grade concrete floors is geotechnically feasible
provided that the subgrade is prepared in accordance with the previous site preparation
' recommendations and the potential for liquefaction induced settlement is considered expectable.
As previously discussed in the Seismic Considerations section of this report, slab -on -grade floors
may be subject to total liquefaction induced surface settlements on the order of 1 to 2 inches.
' We recommend that the structural engineer make provisions in the floor design to minimize the
adverse effects of a potential seismic induced differential settlement on the order of %2 to 1 inch
over a distance of about 30 feet.
' All slab -on -grade floors should be founded on proofrolled or compacted native ground or
structural fill compacted to at least 95 percent of the modified proctor maximum dry density
' determined in accordance with ASTM:D-1557. We recommend that slab -on -grade floors be
underlain by a minimum 6-inch thickness of clean, free draining, well graded mixture of course
sand and gravel to provide uniform support and act as a capillary break. The capillary break
' material should contain less than 3 percent fines, based on that portion passing the U.S. No. 4
sieve.
' In floor slab areas where moisture sensitive floor coverings are planned, an impermeable
membrane (e.g. polyethylene sheet) should be placed directly beneath the slab to act as a vapor
retarder. The vapor retarder should be installed in accordance with ASTM E 1643 "Standard
' Practice for Installation of Water Vapor Retarders Used in Contact with Earth or Granular Fill
Under Concrete Slabs". We recommend a minimum 10-mil polyethylene thickness, or the
minimum thickness specified by the flooring manufacturer, whichever is greater. When concrete
' slabs are cast directly over polyethylene vapor retarders, the concrete water -to -cement ratio must
be correctly specified in order to control bleed water and plastic shrinkage cracking.
' Drainage Considerations
' We recommend that the building be protected by a perimeter footing drain. The drain
should consist of a minimum 4-inch diameter perforated pipe embedded in at least an 18-inch
wide envelope of clean, free -draining, well graded mixture of course sand and gravel. The free-
' 81052440 Johnson Res Report 032907.doc
1
A
Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
81052440
March 29, 2007
Page 19
draining materials should contain less than 5 percent fines, based on that soil fraction passing the
U.S. No. 4 sieve. A non -woven filter fabric such as Mirafi 140N, or equivalent, should envelope
the free -draining granular material.
We .recommend that an under -slab drainage system be installed below the lower level
concrete slab floor. The drainage system should consist of perforated drain lines placed below
the capillary break material of the lower level concrete slab floor. The drain lines should be
equally spaced on approximately 15 foot centers and should consist of 6-inch diameter,
perforated PVC drain pipe placed in excavations 1 foot deep and 1 foot wide. The trenches
should be lined with a non -woven filter fabric such as Mirafi 140N, or equivalent. The trench
' should be backfilled with a clean, free -draining, well graded mixture of coarse sand and gravel
contain less than 3 percent fines, based on that soil fraction passing the U.S. No. 4 sieve.
Subsurface drainage systems including the perimeter footing drains, wall. drains, and
under -slab drains should include permanent cleanouts to allow for potential future maintenance
of the systems. Under -slab drains may be connected to the footing drain system. Roof drains
' should not be connected to the subsurface drainage system. The roof and footing drain system
should be tightlined to a City approved discharge location.
' Final exterior grades should promote free and positive drainage from the building area at
all times. Water must not be allowed to pond or to collect adjacent to foundations or within the
immediate building area. We recommend a gradient of at least 2 percent be provided for a
' minimum distance of 5 feet from the building perimeter, except in paved areas. In concrete or
asphalt paved areas, a minimum gradient of one-half percent should be provided unless
provisions are included for the collection and disposal of surface water adjacent to the structure.
' CLOSURE
' The conclusions and recommendations presented in this report are based on the
explorations accomplished for this study. The number, location, and depth of the explorations
were completed within the site and scope constraints of the project so as to yield the information
' necessary to formulate our recommendations. The plans for this project were in the preliminary
stage at the time this report was written. Under the circumstances, it is recommended that we be
provided the opportunity for general review of the project plans and specifications in order to
confirm that the recommendations and design considerations presented in this report have been
properly interpreted and implemented into the project design package.
' The integrity and performance of the foundation systems at this site depend on proper site
preparation and construction procedures. Field judgment by a qualified engineer will be
necessary in order to determine the adequacy of the site grading, drainage, and foundation
support systems. Therefore, because of our familiarity with the site soils, we recommend that
Zipper Zeman Associates, Inc. be retained to provide geotechnical services during the earthwork
and foundation construction phases of the project. If variations in the subsurface conditions are
' observed at the time of construction, we would be able to provide additional geotechnical
81052440 Johnson Res Report 032907.doc
A
Proposed Single -Family Residence
Lorian Woods Plat, Lot 9
81052440
March 29, 2007
Page 20
engineering recommendations to the contractor and owner in a timely manner as the project
construction progresses.
We appreciate this opportunity to be of service to you, and would be pleased to discuss
the contents of this report or other aspects of the project with you at your convenience.
�0 Ok w a shi r of 1
..03 0
ti
Ettglnesring Geologat '4.
C,ce 1783
Sea
JAMES P. GEORGIS
101
EXPIRES 04 / 0 08
Respectfully submitted,
Zipper Zeman Associates, Inc.
James P. Georgis, L.E.G.
Project Geologist
James B Thompson, P.E.
Principal
Enclosures: Figure 1 — Site and Exploration Plan
Figure 2 — Generalized Geologic Cross Section A -A'
Figure 3 — Static Slope Stability Analysis — Existing Conditions
Figure 4 — Pseudo -Static Slope Stability Analysis — Existing Conditions
Figure 5 — Static Slope Stability Analysis — Construction Conditions
Figure 6 — Static Slope Stability Analysis — Post Construction Conditions
Figure 7 — Pseudo -Static Slope Stability Analysis — Post Construction Conditions
Appendix A — Field Exploration Procedures and Logs
Appendix B — Laboratory Test Procedures and Results
81052440 Johnson Res Report 032907.doc
I
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\ #16121 I I ! 1 1 LEGEND:
I 1 1 / B-1 BORING NUMBER AND
c� 1 1 1 I APPROXIMATE LOCATION
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RIM 84.30 NO PIPES
162ND ST SW IE 12" 97.35
RIM 85.04
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0 20 40
SCALE IN FEET
LEGEND:
B-1 BORING NUMBER
TOP OF BORING
7 STANDARD PENETRATION RESISTANCE IN BLOWS PER FOOT
ST SHELBY TUBE SAMPLE
ATD i GROUNDWATER LEVEL AT TIME OF DRILLING
10/9/06 i GROUNDWATER LEVEL ON DATE INDICATED
BOTTOM OF BORING
NOTES:
THE STRATA ARE BASED UPON INTERPOLATION
BETWEEN EXPLORATIONS AND MAY NOT REPRESENT
ACTUAL SUBSURFACE CONDITIONS. SIMPLIFIED NAMES
ARE SHOWN FOR SOIL DEPOSITS BASED ON
GENERALIZATIONS OF SOIL DESCRIPTIONS.
SEE EXPLORATION LOGS AND REPORT TEXT FOR MORE
DETAILED SOIL AND GROUNDWATER DESCRIPTIONS.
0 20 40
SCALE IN FEET
A
120
100 -
I—
W
W
IL
Z
p 60 -
H
W
J
W
40 -
20 -
0-
PROPOSED -
RESIDENCE
R
B-1
EXISTING GROUND
SURFACE
R
A'
B-2 EXISTING RESIDENCE 120
16121 34TH PLACE WEST
I I ;
I
7
74TH PLACE WEST
FF EL.
92'
5
s
ST /
F F E LF82.8'
10/9/06
12
V46/06
8
�? /
10/9/06
=11/16/06
ST
20
Medium stiff to stiff, silty
8
CLAY to clayey SILT with
variable sand content and
13
loose SAND with variable
/ /
i
18
silt content. (Colluvium)
444
/
y /
25
/
/
8
� /
/
/
�
/
/
35
18 /
Very stiff to hard, massive
to finely laminated, clayey
/
27
SILT. (Whidbey Forrnatiori)
Loose to medium dense
/
24
SAND with variable silt
^
content.
(Possible Colluvium)
Medium dense, interbedded,
silty SAND and sandy SILT.
t
i
(Possible Colluvium)
f
100
H
W
W
IL
Z
60 p
H
W
J
W
M
20
125
100
a 75
W
c/)
X
Q 50
25
0
Existing Slope Conditions - 10 most critical surfaces
Existing
Minimum Bishop FOS for Static Conditions = 2.2 Foundation
Surcharge
0 25 50 75 100 125 150 175 200
X—AXIS (feet)
SOIL PROPERTIES
(1)
Colluvium, 0=0
C=900 psf
(2)
Colluvium, 0=32 °,
C=0 psf
(3)
Colluvium, 0=36 °,
C=0 psf
(4)
Whidbey Formation,
0=0 °, C=2000 psf
125
••l
a 75
a�
_N
X
Q 50
25
C•;
Existing Slope Conditions - 10 most critical surfaces
Existing
Minimum Bishop FOS for Pseudo -Static Conditions = 1.1 Foundation
Surcharge
SOIL PROPERTIES
(1)
Colluvium, 0=0 °,
C=900 psf
(2)
Colluvium, 0=20 °,
C=0 psf
(3)
Colluvium, 0=36 °,
C=0 psf
(4)
Whidbey Formation,
0=0 °, C=2000 psf
0 25 50 75 100 125 150 175 200
X—AXIS (feet)
ZIPPER ZEMAN ASSOCIATES, INC. Project No. 81052440 Johnson Residence
Date: March 2007 Edmonds, Washington
GEOTECHNICAL AND ENVIRONMENTAL Scale: As Noted
CONSULTING Figure 4 : Pseudo -Static Slope Stability Analysis
Existing Conditions
125
100
a 75
aD
to
X
Q 50
25
n
Slone Conditions During Construction - 10 most critical surfaces
Existing
Minimum Bishop FOS for Static Conditions = 1.6 Foundation
Surcharge
0 25 50 75 100 125 150 175 200
X—AXIS (feet)
SOIL PROPERTIES
(1)
Colluvium, 0=0
C=900 psf
(2)
Colluvium, 0=32 °,
C=0 psf
(3)
Colluvium, 0=36°,
C=Opsf
(4)
Whidbey Formation,
0=0 °, C=2000 psf
M M M M M M M M M M
125
100
0--.
i 75
m
to
X
Q 50
25
U
Post Construction Slope Conditions - 10 most critical surfaces
Existing
Minimum Bishop FOS for Static Conditions = 2.0 Foundation
Surcharge
SOIL PROPERTIES
(1)
Colluvium, 0=0 °,
C=900 psf
(2)
Colluvium, 0=32 °,
C=0 psf
(3)
Colluvium, 0=36°,
C=0 psf
(4)
Whidbey Formation,
0=0 °, C=2000 psf
0 25 50 75 100 125 150 175 200
X—AXIS (feet
ZIPPER ZEMAN ASSOCIATES. INC. Project No. 81052440 Johnson Residence
Date: March 2007 Edmonds, Washington
GEOTECHNICAL AND ENVIRONMENTAL Scale: As Noted
CONSULTING Figure 6 : Static Slope Stability Analysis
Post Construction Conditions
125
100
m 75
to
X
Q 50
►;
25
0
Post_ Construction Slope Conditions - 10 most critical surfaces
Existing
Minimum Bishop FOS for Pseudo -Static Conditions = 1.1 Foundation
Surcharge
0 25 50 75 100 125 150 175 200
X—AXIS (feet)
SOIL PROPERTIES
(1)
Colluvium, 0=0
C=900 psf
(2)
Colluvium, 0=20 °,
C=0 psf
(3)
Colluvium, 0=36 °,
C=0 psf
(4)
Whidbey Formation,
0=0 °, C=2000 psf
APPENDIX A
FIELD EXPLORATION PROCEDURES AND LOGS
APPENDIX A
FIELD EXPLORATION PROCEDURES AND LOGS
81052440
Our field exploration for this project included 2 borings completed on June 22,
2006. The approximate exploration locations are shown on the Site and Exploration
Plan, Figure 1. The exploration locations and elevations were taken from a site specific
survey completed by Greene Land Surveying dated August 8, 2006. Descriptive logs of
the explorations. are enclosed in this appendix. The following sections describe our
procedures associated with the exploration.
The exploratory borings were advanced with a hollow stem auger, using a track -
mounted drill rig operated by an independent drilling company working under subcontract
to ZZA. An experienced geologist from our firm continuously observed the borings,
logged the subsurface conditions encountered, and obtained representative soil samples.
All samples were stored in moisture -tight containers and transported to our laboratory for
further visual classification and testing. After each boring was completed, the borehole
was backfilled with bentonite and soil cuttings.
Throughout the drilling operation, soil samples were obtained at 2.5- to 5-foot
depth intervals by means of the Standard Penetration Test (ASTM: D-1586). This testing
and sampling procedure consists of driving a standard 2-inch outside diameter steel split
spoon sampler 18 inches into the soil with a 140-pound hammer free falling 30 inches.
The number of blows required to drive the sampler through each 6-inch interval is
recorded, and the total number of blows struck during the final 12 inches is recorded as
the Standard Penetration Resistance, or "blow count" (N value). If a total of 50 blows is
struck within any 6-inch interval, the driving is stopped and the blow count is recorded as
50 blows for the actual penetration distance. The resulting Standard Penetration
Resistance values indicate the relative density of granular soils and the relative
consistency of cohesive soils.
The enclosed boring logs describe the vertical sequence of soils and materials
encountered in each boring, based primarily upon our field classifications and supported
by our subsequent laboratory examination and testing. Where a soil contact was observed
to be gradational, our logs indicate the average contact depth. Where a soil type changed
between sample intervals, we inferred the contact depth. Our logs also graphically
indicate the blow count, sample type, sample number, and approximate depth of each soil
sample obtained from the boring, as well as laboratory tests performed on these soil
samples. If groundwater was encountered in a borehole, the approximate groundwater
depth, and date of observation, are depicted on the log.
Groundwater observation wells were installed in borings B-1 and B-2. The
observation wells consisted of a length of slotted 1-inch PVC pipe placed in the borehole.
A blank PVC riser extended from the lower slotted section to the ground surface.
Washed silica sand was utilized to backfill the annular space between the slotted interval
and the borehole to allow entry of water into the well, while a mixture of bentonite was
used to backfill around the blank riser. A concrete surface seal and metal monument
cover were placed at the surface. Groundwater levels measured in the observation wells
subsequent to completion of drilling are indicated on the log, along with the date of
measurement. This information is also discussed in the text.
The boring logs presented in this appendix are based upon the drilling action,
observation of the samples secured, laboratory test results, and field logs. The various
types of soils are indicated as well as the depth where the soils or characteristics of the
soils changed. It should be noted that these changes may have been gradual, and if the
changes occurred between samples intervals, they were inferred.
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-1 PAGE 1 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 90.5 Feet
Soil Description
N �
-0
Penetration Resistance
a
a
d
c�
,r
c
oM
=
Standard Blows per foot Other
j
0
to Z
01
0 10 20 30 40 5
Z
d
~
0
_.
------------------------------------------------ I
Medium stiff, moist to wet, gray -brown, silt CLAY with y Y
some fine sand. Slight iron oxide staining. Blocky,
disturbed texture. (Colluvium)
--------------
_____________
5 _
S-1 . ' I i 6
L_
(Moist unit weight 95.5 pcf) --T-------'-- --*--r--'---,---
S-1A I ' I ' •'
---;----r--'-- 1--'-------I---
I
-------------
T
1 0
1-inch thick sand seam observed at 11 feet.
S-2
(Colluvium) PP = 3.25 tsf 8 Att.
T r
11/16/06
10/9/06 I I 1 1
---,--T--�--r--�---I-- �--+--r--------------
-
I
_T_
15
Loose, saturated, gray, silty SAND with trace fine o ' 6 20OW
organic material. (Colluvium)
________________________________________________
Medium stiff, wet, gray, silty CLAY with trace to some 1
20
fine sand. Disturbed, blocky texture with inclusions of T
hard, angular clayey SILT. (Colluvium) S-4 1
PP=3.5tsf --- -- •'---I-- L-----'-- 8
-------------
1 ' I '
_' I
- I ,-- -7--�--r--I---
- 25
Explanation
Monitoring Well Key Moisture Content
I2-inch O.D. split spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
IF 3-inch I.D Shelby tube sample Bentonite
Testing Key
® No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Att. = Atterberg Limits
ATD or date of measurement
UCT = Unconfined Compression Test
ZZA ❑ Blank Casing PP = Pocket Penetrometer
711pner Zeman ASSociatPc, Inc. BORING LOG Figure A-1
Geotechnical and Environmental Consulting Date Drilled: 06/22/2006 Logged By: JPG
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-1 PAGE 2 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 90.5 Feet
Soil Description
a
Penetration Resistance
H
R
ow
F
N
A=
o
Standard Blows per foot Other
25
N Z
U'
0 10 20 30 40 5
Z
t)
Grades to stiff and moist to wet.
PP - 3.5 tsf
S-5
, 1
I I I , 1 , ,
13
Att.
-------------
-------------
T
, __I___I _ - -_
I I I I I I I I I
- 30
-------------------------------------------
Loose to medium dense, saturated, gray, silty, fine
S6
- - - - - - - - -
14
SAND. (Colluvium)
--------------
.
-------------
-=-----------
- - - - -' - - -, - - - - - r - -'- - -, - -
I I I I I -
-
35
Grades to medium SAND with trace silt
Medium dense, saturated, gray, interbedded, fine
-------------
S-7
-J r �I
1
J
t - • '•
___
�' ,
T - - -- 'J - --
I__T It__
__ i__r___
8
200W
silty,
to medium SAND and fine sandy SILT.
k
, I , 1 I I I 1 I
(Possible Colluvium)
_
40-
1-inch thick organic seam observed at 40 5 feet.
S-8,
, 1 , 1
' I .' I I
18
- -
- --
I
Gradestoto silty, fine SAND.
--
S 9
--'-
*
20
45
Grades to interbedded, silty, well graded SAND with
trace clay and fine to medium SAND.
-----------------------------------------------
Very stiff, saturated, gray, thinly bedded SILT with
--
----- -----
S-10
:;
- - ,- - -'- - -r - - - r
'
26
trace
to some fine sand. (Whidbey Formation)-'
--------------
-------------
-------------
_ Y _ _ L _ _ r _ _ _ _
50
Explanation
Monitoring Well Key Moisture Content
I 2-inch O.D.
split spoon sample Clean Sand Plastic Limit Natural Liquid Limit
3-inch I.D Shelby tube sample Bentonite
® Testing Key
No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Att. = Atterberg Limits
ATD
or date of measurement
UCT = Unconfined Compression Test
❑ Blank Casing PP = Pocket Penetrometer
Zipper Zeman Acco iatec', Inc BORING LOG Figure A-1
Geotechnical and Environmental Consulting Date Drilled: 06/22/2006 Logged By: JPG
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-1 PAGE 3 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 90.5 Feet
Soil Description
Penetration Resistance
0
m
0 so
Standard Blows per foot Other
j
o
Cl)
0Z
C9�
0 10 20 30 40 5
Z
50
Grades to very stiff, moist, greenish -gray, clayey SILT. 1•
Inch thick overconsolldaled organic seam observed at
50 5 feet.
-------------
S 11
::
.tom,
_' 1
___r __I___I__1
27
' 1
55
Grades to moist to wet, gray, finely laminated, clayey
SILT. PP = 4.5 tsf
----- ------
-------------
S-12
� -
'_ _ _ _' _ _ 1 _. _ _ _
- - I L _ _1 , I I I_ - -,- - -_ _ _
,
I I I
24
Boring completed at 56.5 feet on 06/22/2006.
Groundwater observed at 15.5 feet at time of drilling.
Groundwater measured at 12.6 feet on 10/09/2006.
--------------
- " T - -'" - -- - -'- - - - - ` - - r - - - - -'- - -
Groundwater measured at 11.4 feet on 11 /16/2006.
_____________
_ 7 _ _ L _ _ r _ _1_ _ .y _ _ 1 _ _ }. _ _ I_ _ _1_ _ _
60
-------------
I ' I ' I
- y - - L-
I
_____________
_____________
1 '
T--i --t--1--�----r--� --
_____________
1
1
'
7 _ _ _ _ _ r _
65
-------------
_____________
_,_ _ _I _ _ .{ _ _ _ _ - _ _1_ _ _I
__ L 1 1 I 1 ' 1
_____________
_ I_ _ _I _ _ J - _ _ _ L - _ 1_ _ _1
1
_____________
_ _. _ 1_ _ J _ I , ' ,
_____________
70
-------------
T
I
-------------
1-
_____________
I
_ _ 1 _ _ _ _ I_ _ _' _ _ I -r--1---
75
I
Explanation
Monitoring Well Key Moisture Content
I2-inch O.D. split spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
3-inch I.D Shelby tube sample ® Bentonite I
Testing Key
® No Recovery Grout/Concrete GSA = Grain Size Analysis
20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Aft. = Atterberg Limits
ATD or date of measurement UCT = Unconfined Compression Test
❑ Blank Casing PP = Pocket Penetrometer
ZZA Zipper Zeman Associates-., Inc.
BORING LOG
Figure A-1
Geotechnical and Environmental Consulting
Date Drilled: 06/22/2006
1 Logged By: JPG
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-2 PAGE 1 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 103 Feet
Soil Description
Penetration Resistance
a
rn
oto
y Z
0
Standard Blows per foot Other
Z
0 10 20 30 40 5
------------------------------------------------
Medium stiff, moist to wet, mottled gray -brown silty
-----------
- - - - - -, - - i - _ _ _ _ _ 1- - _� _
CLAY with some sand. Disturbed, blocky texture.
(Colluvium)_____________
------------- _ _I _
r - -'- - 7 - - - - - - -I- - - 4 - -
LAA
ixx
-------------DQ<-�-----'----'--'---'---'--J-
--
5 -
I
S-1 ,. 7
--------------------------------------------- __
Loose, moist, gray -brown, fine SAND with some silt. - L - - - - - - - - -, -
Slight to moderate iron oxide staining. (Colluvium)
- - ,- - - r - -,- -- -I - - j - - _ - - -'- - -I - - -
------------------------------------------------
r
Medium stiff, wet, mottled gray -brown clayey SILT with - -- ------
-�--�-r---
some sand. Disturbed, blocky texture. (Colluvium) - -I- - -I
S_2 4 5
L
________________________________________________
10 Stiff, moist to wet, gray, clayey SILT. Disturbed, blocky -- _ _ _ - --
---- ---- --
texture with inclusions of hard, clayey SILT. S-3 g
(Colluvium) PP = 3.5 tsf
T
--- - - -' - 1
1 --� - -r --,-- -I-- --+- -� --
Loose, saturated, gray, silty, fine SAND. (Colluvium) S-4 ATD ; 7
------+--T --'------'---i--i--r--
I
15
----------------------'-----1 `----------------- 1
-5
Medium stiffto stiff, moist, gray, clayey SILT with trace -- -- _ _ _ _'_ - -I _ _ I
fine sand. Blocky texture. (Colluvium) PP = 3 tsf
Wet unit weight = 118 pcf
-----------------------------------------
Loose, saturated, gray, silty, fine SAND. (Colluvium)
--------------------------------------------- _ _ _ I- - -'- - -' - -
----- ---- -
Stiff, moist, gray, finely laminated, clayey SILT. S 6 - - - - - -I- - - - - -
(Colluvium) . 12
My__ _ _-- _
20 _ 11/16/06 1
___ YK I
Grades to saturated, interbedded, finely laminated, S-7 1o/s/os 11
clayey SILT and fine, sandy SILT. PP = 2.5 tsf _____ ______
---------------
_I__
Medium dense, saturated, gray, fine SAND with some------------
silt.
(Possible Colluvium)
. 25
1 I I I I I
Explanation
Monitoring Well Key Moisture Content
I2-inch O.D. split spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
3-inch I.D Shelby tube sample Bentonite
Testing Key
® No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Aft. = Afterberg Limits
ATD or date of measurement
UCT = Unconfined Compression Test
ZZA ❑ Blank Casing PP = Pocket Penetrometer
7iR er Zeman A socia c., Inc- BORING LOG Figure A-2
Geotechnical and Environmental Consulting Date Drilled: 06/22/2006 Logged By: JPG
UCT 1
j
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-2 PAGE 2 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 103 Feet
Soil Description L a Penetration Resistance w
Gf L
om F A 3 3 Standard Blows per foot Other j vt
In to Z U' Z fd
0 10 20 30 40 5
25
S-8
e% y
I I I I I I
— —
S-9 " "
Grades to fine sandy SILT. '�, -' r 20 20OWI
30
Grades to silty fine SAND. 3-inch thick, stiff, clayey g_10
SILT seam observed at 30.5 feet. _ _ - _ _I _ _
- I I I I
I
-------------
--------------
I
7--�--I---'--�——�——r——'——-I---
..
1 I
35
.{
___ L_ _ y _ _ )_ _�_
Grades to loose, silty SAND with trace clay.
S-11 .: ::: . 9
-----------------------------------------------
Very stiff, moist to wet, gray, finely laminated, clayey
SILT with trace fine sand partings
I
(Whidbey Formation)-
...
-------------
------------
———I——*—— r — —�——i——'————i——r——
40
� I I
S-12l ?- 18
I
{-
45
PP>4.5tsf - -; -- ----*--T--------,--
S-13 * 25
- -
I
-+ _r-
-'-------------I--
I
- - - - - - - - - - - - - -..:.' -'-.: - �- - -'- - - I- - -' - - '- - -'- - -' -
50
Explanation
Monitoring Well Key Moisture Content
I2-inch O.D. split spoon sample ❑ Clean Sand Plastic Limit Natural Liquid Limit
R3-inch I.D Shelby tube sample Bentonite
Testing Key
® No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Att. = Atterberg Limits
ATD or date of measurement
UCT = Unconfined Compression Test
ZZA ❑ Blank Casing PP = Pocket Penetrometer
7ipner Zeman A oarp��lBORING LOG Figure A-2
Geotechnical and Environmental Consulting Date Drilled: 06/22/2006 Logged By: JPG
PROJECT: Johnson Residence JOB NO.: 81052440 BORING: B-2 PAGE 3 OF 3
Location: Edmonds, WA Approximate Surface Elevation: 103 Feet
Soil Description
Penetration Resistance
s
a CL
0
rn
c
oR
FT.
3
0"
Standard Blows per foot Other
j
N
CO Z
U'
0 10 20 30 40 5
Z
50
Grades to hard, moist, gray, finely laminated, clayey
SILT. PP > 4.5 tsf
-
S-14
♦
T
35
--------------
Boring completed at 51.5 feet on 06/22/2006.
Groundwater observed at 13.5 feet at time of drilling.
Groundwater measured at 20.3 feet on 10/09/2006.
-I -
Groundwater measured at 19.3 feet on 11/16/2006.
- 55
------------
-------------
_____________
-------------
-------------
L _ _ 1 1
1 ' I
--7--�--i--'--'I--� --r--I---I---
I I I I I
'
I- - _I_ _ _
I I I I
' 60
1 I I I 1
' 1 1
-------------
_____________
_____________
_____________
1
I
I '
T
65
I '
-------------
-------------
_I _y__1__F__
_____________
I ' __
___1___I__,_____
_____________
I
I I I I I
I I
70
___ __________
I 1 I I I
-------------
_____________
_____________
I I 1 I I I I I I
L _ _ _I _ _ _ _ _ _ - _ _'_ _
'_ _ _ I_ _ _' _ _ J _ -- I I 1 I
' I I
75
I I I I
Explanation
Monitoring Well Key
Moisture Content
I2-inch O.D. split spoon sample ❑ Clean Sand
Plastic Limit Natural Liquid Limit
3-inch 1.13 Shelby tube sample Bentonite
1
Testing K
® ew
No Recovery Grout/Concrete GSA = Grain Size Analysis
. 20OW = 200 Wash Analysis
Groundwater level at time of drilling ® Screened Casing Aft. = Atterberg Limits
ATD or date of measurement
UCT = Unconfined Compression Test
ZZA ❑ Blank Casing PP = Pocket Penetrometer
Zipper Zeman Associates, Ins. BORING LOG Figure A-2
I
Geotechnical and Environmental Consulting Date Drilled: 06/22/2006 Logged By: JPG
APPENDIX B
LABORATORY TESTING PROCEDURES AND RESULTS
APPENDIX B
' LABORATORY TESTING PROCEDURES AND RESULTS
81052440
' A series of laboratory tests were performed during the course of this study to
evaluate the index and geotechnical engineering properties of the subsurface soils.
Descriptions of the types of tests performed are given below.
Visual Classification
' Samples recovered from the exploration locations were visually classified in the
field during the exploration program. Representative portions o the same es were
carefully packaged in moisture tight containers and transported to our laboratory where
' the field classifications were verified or modified as required. Visual classification of soil
was generally done in accordance with the Unified Soil Classification system. Visual soil
classification includes evaluation of color, relative moisture content, soil type based upon
grain size, and accessory soil types included in the sample. Soil classifications are
presented on the exploration logs in Appendix A.
' Moisture Content Determination
' Moisture content determinations were performed on representative samples
obtained from the exploration in order to aid in identification and correlation of soil
types. The determinations were made in general accordance with the test procedures
described in ASTM: D-2216. The results are shown on the exploration logs in Appendix
A.
U.S. Number 200 Wash
This test procedure determines the amount of material finer than a U.S. No. 200
sieve by washing. The determinations were made in general accordance with the test
procedures described in ASTM: D-1140. The results of the U.S. No. 200 wash
determinations for the samples were used in classification of the soils, and are presented
in this appendix.
Atterberg Limits
Atterberg
limits are used primarily for classification and indexing of cohesive
' soils. The liquid and plastic limits are two of the five Atterberg limits and are defined as
the moisture content of a cohesive soil at arbitrarily established limits for liquid and
plastic behavior, respectively. Liquid and plastic limits were established for selected
samples in general accordance with ASTM: D-423 and ASTM: D-424, respectively. The
results of the Atterberg limits are presented on a plasticity chart in this appendix where
the plasticity index (liquid limit minus plastic limit) is related to the liquid limit. The
1!
plastic limits and liquid limits are also presented adjacent to appropriate samples on the
exploration logs in Appendix A.
In -place Density
The in -place density of some site soils was determined by computing the volume
of a portion of the undisturbed samples from the boring explorations then weighing the
sample. The in -place densities computed is presented on the boring logs in Appendix A.
Unconfined Compression Test
In order to determine the undrained shear strength of a representative sample of
the cohesive soils encountered in the borings, an unconfined compression test was
conducted in general accordance with the ASTM: D-2166 test procedure. The test was
performed by trimming an undisturbed Shelby tube sample to a length of approximately 6
inches. Axial loading was then applied to the specimen (zero confining pressure) at a
constant rate of strain. The results of this test are presented in this appendix and on the
appropriate boring log. The undrained shear strength of a cohesive soil is generally
considered equivalent to one-half its unconfined compressive strength.
Pocket Penetrometer
A calibrated hand device, a Pocket Penetrometer (PP), was utilized on relatively
undisturbed fine-grained soil samples. This device consists of a spring -loaded ram that is
forced into the soil sample by hand pressure and the amount of spring resistance required
' for penetration provides an indication of the unconfined compressive strength. The
results of these tests are presented on the boring logs in Appendix A in tons per square
foot (tsf). The undrained shear strength of a cohesive soil is generally considered
equivalent to one-half its unconfined compressive strength.
1
11
60
PLASTICITY CHART
ASTM D 4318
ZEE
50
40
eH
Q
C
30
v
R
a
20
10
7
4
0
0 10 20 30 40 50 60 70 80 90 100
Liquid Limit %
U_line—
-line_
-------
---- ---
----
— -Ino
------high-plasticity
panic -slays
of
—
—
-Low.p a ti
inorganic
——Micaceous
diatomace
us_fine—
clays; san
y and
s�ndy-and-sil
y-soils; ela
tic -silts=-
-silty-clays-
-Medium
ganic-sit
lays, -and
'tty-clays-
_
plas is
--
inoraan�
_.
OR
—Silty-el
ys=-
---
-
--days
or
�lagey
tits
C-L
MIJ—_
and sa
ds
OL
--I
o
organi�an
-towplasti '
-organic-sil
y; roek-floe
-and-silt
;silty -silty -el
ays
yey
_ _
CGML
_ _ _
-
-
-
M
i
e sands
USCS
Received
Liquid
Plastic
Plasticity
1
UNCONFINED COMPRESSION TEST
Project Johnson Residence Job No. J-81052440
Location of Project Edmonds WA
Description of Soil Boring B-2 S-5 (Clayey SILT with trace to some fine sand)
Tested By JPG Date of Testing 02/15/2007
Sample Data
Diameter 2.9 in Area A o 6.47 in Height, L o 5.16 in
Volume 0.0193 ft3 Weight 2.28 lb Wet unit weight 118.1 pcf
Water content, w% 30 Dry unit wt. 90.8 pcf LRC = 1.761"(dial)+6 8645
Deformation
dial
reading
(x 103)
Load
dial
(units)
Sample
deformation
AL,, in.
(col. 1 x 10,3)
Unit
strain
4L/Lo
Area
CF
1 - a
Corrected
area, A',
sq in.
Total
load on
sample
(col. 2 x LRC)
Sample
unit
load, psi
1
2
3
4
5
6
7
8
20
7
0.020
0.0039
0.9961
6.49
19
2.96
40
10
0.040
0.0078
0.9922
6.52
24
3.76
60
13
0.060
0.0116
0.9884
6.54
30
4.55
80
16
0.080
0.0155
0.9845
6.57
35
5.34
100
20
0.100
0.0194
0.9806
6.59
42
6.38
120
24
0.120
0.0233
0.9767
6.62
49
7.42
140
28
0.140
0.0271
0.9729
6.65
56
8.45
160
31
0.160
0.0310
0.9690
6.67
61
9.21
180 _
35
0.180
0.0349
0.9651
6.70
68
10.22
200
38
0.200
0.0388
0.9612
6.73
74
10.97
220
41
0.220
0.0426
0.9574
6.75
79
11.71
240
43
0.240
0.0465
0.9535
6.78
83
12.18
260
46
0.260
0.0504
0.9496
6.81
88
12.90
280
49
0.280
0.0543
0.9457
6.84
93
13.62
300
51
0.300
0.0581
0.9419
6.87
97
14.08
320
52
0.320
0.0620
0.9380
6.89
98
14.28
340
54
0.340
0.0659
0.9341
6.92
102
14.73
360
55
0.360
0.0698
0.9302
6.95
104
14.92
380
56
0.380
0.0736
0.9264
6.98
105
15.11
400
56
0.400
0.0775
0.9225
7.01
105
15.05
420
57
0.420
0.0814
0.9186
7.04
107
15.24
440
57
0.440
0.0853
0.9147
7.07
107
15.17
460
57
0.460
0.0891
0.9109
7.10
107
15.11
480.
55
0.480
0.0930
0.9070
7.13
104
14.55
500
54
0.500
0.0969
0.9031
7.16
102
14.24
520
53
0.520
0.1008
0,8992
7.19
100
13.93
540
51
0.540 1
0.1047
0.8953
7.22
97
13.39.
Unconfined compressive strength q , = 15.24 psi
Cohesion = q /2 = 7.62 psi
ZIPPER ZEMAN ASSOCIATES, INC PROJECT NO: J-81052440 PROJECT NAME:
GEOTECHNICAL AND ENVIRONMENTAL DATE OF TESTING: 02/15/2007 Johnson Residence
CONSULTING