SKJVgeotech8.06.pdfy
Associated Earth Sciences, Inc.
N IE N WJ a
Cefefi6 y25 Voff ofYerdee
August 2, 2006
Project No. KE060165A
Soundview Homebuilders
9026 6' Avenue South
Edmonds, Washington 98020
Attention: Mr. Ron Den Adel
AUS 0 i 2006
BtifL0
CIT
1f1V0 DLPRR7MENT
° OF
EDM
NO$
Subject: Response to City of Edmonds
Proposed Rockery Construction
1.7037 76`h Avenue West
Edmonds, Washington
Dear Mr. Den Adel:
s
As requested, Associated Earth Sciences, Inc. (AESI) is pleased to provide this letter in
response to the City of Edmonds requirements for the proposed rockery construction at the
above -referenced site. As required by the City of Edmonds and reiterated in our telephone
discussion with Mr. Dave Gebert and Mr. Lyle Christman of the City of Edmonds, this letter
specifically addresses the requirements of Handout #63, Section 6, Rockery Design
Calculations.
Attached to this letter is a geotechnical report for the project prepared by AESI in April 2006,
and two rockery design details. This report provides the following information pertinent to the
requirements of Section 6 of Handout #63:
Soil Classification:
Allowable Bearing Pressure
Active Earth Pressure:
Passive Earth Pressure:
Coefficient of Friction:
Pre -Fraser Glacially Consolidated
USC: SM -ML
1,500 psf
40 pcf unrestrained
55 pcf restrained
250 psf
0.35
Land Office • 911 FifthAvenue, Suite 100 • Kirldand, WA 98033 • P (425) 827-7701 • F (425) 827-5424
Everett Office • 2911112 HewittAvenue, Suite 2 • Everett, WA 98201 • P (425) 259-0522 • F (425) 252-3408
www.aesgeo.com
Seismic Loads (per IBC 2003):
period w 0.2 seconds: 1.22g
Period = 1 second: 0.43g
Water Table Information: Minor seasonal seepage at 2 feet
Maximum Slope Behind Rockery: 211: 1V (Horizontal:Vertical)
Rock Specifications:
See attached details
Based on the above -referenced geotechnical report, in our opinion, the potential for the site
soils to liquefy during a large earthquake is low due to their high density and silt content.
Based on experience, we would estimate the moist unit weight of the native soils to be
approximately 130 pounds per cubic foot (pcf). To our knowledge, based on review of the
project plans, there are no additional surcharges applied to the rockeries.
We appreciate the opportunity to be of service to you on this project. Should you have any
questions regarding this letter or other geotechnical aspects of the project, please call us at
your earliest convenience.
Sincerely,
ASSOCIATED EARTH SCIENCES, INC.
Kirkland, Washington
EXPIgES 2 / / �,
Jon N. Sondergaard, P. G., P.E.G. Matthew A. Miller, P.E.
Principal Engineering Geologist Associate Engineer
Attachments: Subsurface Exploration and Geotechnical Engineering Letter -Report
Unreinforced Rockery Detail
Terraced Rockery Detail
rxsria
KE060165A2
Proj ects1200601651KE1W P
Associated Earth Sciences, Inc.
0 LE N 9;1 0'
Cefe&abny25 Vam o f &etw
April 10, 2006
Project No. KE060165A
Soundview Homebuilders
902 6"' Avenue South
Edmonds, Washington 98020
Attention: Mr. Ron Den Adel
Subject: Subsurface Exploration and Geotechnical Engineering Letter -Report
17039 76" Avenue West - Lot 3
Edmonds, Washington
Dear Mr. Den Adel:
Associated Earth Sciences, Inc. (AESI) is pleased to present this letter -report summarizing the
results of our subsurface exploration and providing design criteria for foundations and rockeries
for the proposed home to be built on Lot 3 of the subject property. A geotechnical report is
required for this property based on Section 19.10 of the City of Edmonds Municipal Cade for
property with slope inclinations exceeding 15 percent, and City of Edmonds review comments
issued for your project on December 28, 2005.
Subsurface Exploration
We completed one exploration pit (EP -1) in the building envelope for Lot 3 on January 2, 2006.
We encountered 12 inches of topsoil over 1 foot of loose silty sand with roots overlying brown
grading to gray, medium stiff grading to hard, sandy silt to the maximum depth explored of
10 feet (approximate elevation 11.8). Elevation estimates are based on plotting the exploration
pit location on a site survey provided by you (Figure 1). Very slow, perched ground water
seepage was observed at a depth of 2 feet within exploration pit EP -1. The seepage depth
represents the contact between the loose surficial sediments and underlying denser sediments.
Samples were collected at each strata change.
We interpreted the sand to be Vashon advance outwash and the silt to be pre -Fraser sediments
consistent with those mapped on the "Composite Geologic Map of the Sno-King Area, " Booth et
al_, 2004. Advance outwash consists of sand that has been deposited in front of an advancing
glacial ice sheet and has been overridden by several thousand feet of glacial ice. Pre -Fraser
fine-grained sediments are sediments deposited in a large proglacial lake formed by ice dams
that blocked the outlet to the Pacific Ocean prior to the advance of the ice sheet that eventually
covered the Puget Sound area during the Fraser Glaciation. As such, this material has also
been over -consolidated by the weight of glacial ice.
Kirkland OfTce • 911 Fifth Avenue, Suite 100 • Kirkland, WA 95033 • P (425) 827-7701 • F (425) 827-5424
1 Ewa Office • 29111/2 HewittAvenue, Suite 2 • Ev=M WA 98201 • P (425) 259-0522 • F (425) 252-3408
www:aesgeo.com
Recommendations and Design Criteria
Erosion Mitigation Measures
The site slopes are defined as Erosion Hazard Areas by the City of Edmonds. The surface
sediments underlying the site generally contain silt and fine sand and will be sensitive to
erosion and moisture, especially in the sloping portions of the site. In order to reduce the
amount of sediment transport off the site during construction, the following recommendations
should be followed.
1. Temporary silt fencing should be placed around the lower perimeter of all cleared
area(s) and at the base of sloped areas. The fencing should be periodically inspected
and maintained, as necessary, to ensure proper function.
2. To the extent practical, earthwork -related construction should proceed during the drier
periods of the year, and disturbed areas should be revegetated as soon as possible.
Temporary erosion control measures should be maintained until permanent erosion
control measures are established.
3. Areas stripped of vegetation during construction should be mulched and hydroseeded,
replanted as soon as possible, or otherwise protected. During winter construction,
hydroseeded areas should be covered with clear plastic to facilitate grass growth.
4. If excavated soils are to be stockpiled on the site for reuse, measures should be taken to
reduce the potential for erosion from the stockpile. These could include, but are not
limited to, covering the pile with plastic sheeting, the use of low stockpiles in flat areas,
and the use of straw bales/silt fences around stockpile perimeters.
5. To the extent necessary, interceptor swales with rock check dams should be constructed
to divert storm water from construction areas and to route collected storm water to an
appropriate discharge location.
6. A rock construction entrance should be provided to reduce the amount of sediment
transported off-site on truck tires.
7. All storm water from impermeable surfaces, including driveways and roofs, should be
tightlined into approved facilities and not be directed onto or above steeply sloping
areas.
Temporary Cut Slopes
Review of the project plans indicate that cuts up to 13 feet high along the east side of the house
will be required to obtain the design basement floor elevation. in our opinion, stable
construction slopes should be � regponsibility of the contractor, and should be determined
during construction based on actual soil and ground water conditions encountered. For
estimating purposes, we anticipate that temporary, unsupported cut slopes in the advance
2
outwash sand and underlying pre -Fraser silt can be planned at 1H:1V (Horizontal: Vertical) or
flatter. Temporary, vertical cuts should be no taller than 4 feet. Permanent cut or structural
fill slopes should not be steeper than 2H: 1V.
These slope angles are for areas where ground water seepage is not encountered, and assume
that surface water is not allowed to flow across the slope faces. If ground or surface water is
present when the excavation slopes are exposed, flatter slope angles or shoring may be
required. As is typical with earthwork operations, some sloughing and raveling may occur,
and cut slopes may have to be adjusted in the field. In addition, WiSHA/OSHA regulations
should be followed at all times.
EngineeringEngineerigg Design Criteria
Based on our calculations, the basement retaining walls for the structure must be completely
founded within the dense to very dense natural soils in order to reduce the risk of slope failure
along the sand/silt depositional plane that is characteristic of the failure mechanism within the
Meadowdale Landslide Complex. Interior spread footing foundations, and the west and
portions of the north and south walls of the home, can be founded in medium dense to dense,
brown or gray sand. For the residential structure founded on the prescribed bearing stratum,
spread footings may be designed for an allowable foundation soil bearing pressure of 1,500
pounds per square foot (psf), including both dead and live loads.
This bearing pressure is also appropriate for approved granular on-site or imported structural
fill, compacted under our observation and testing to at least 95 percent of American Society for
Testing and Materials (ASTM):D 1557 and to a firm, non -yielding condition, as determined by
the geotechnical engineer or their representative. The on-site sand is appropriate for structural
fill use. However, the silt is not considered appropriate for use as structural fill due to its
extreme moisture sensitivity. Soils in which the amount of fine-grained material (smaller than
the No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve
size) should ,be considered moisture -sensitive. Use of moisture -sensitive soil in structural fills
should be limited to favorable dry weather and dry subgrade conditions.
If fill containing moderate quantities of silt is placed during wet weather or if proper
compaction cannot be obtained, a select material consisting of a clean, free -draining gravel
and/or sand should be used. Free -draining fill consists of non-organic soil with the amount of
fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve
fraction and at least 25 percent retained on the No. 4 sieve.
These recommendations are predicated on a member of our firm observing footing foundation
excavations to determine if the proper bearing capacity has been reached. Anticipated
settlement of footings founded as recommended should be on the order of Y4 inch or less, with
differential settlement of 1/2 inch or less. However, disturbed material not removed from
footing trenches prior to footing placement could result in increased settlements.
3
Structural design of the residence should follow 2003 ,International Building Code (IBC)
standards using Site Class "D" as defined in Table 1615.1.1. The 2003 IBC seismic design
parameters for short period (Ss) and 1 -second period (Si) spectral acceleration values were
determined by the latitude and longitude of the project site using the United States Geological
Survey (USGS) National Seismic Hazard Mapping Project website
(http:I/earthquake.usgs.govlhazmapsl). Based on the more current 2002 data, the USGS
website interpolated ground motions at the project site to be 1.22g and 0.438 for building
periods of 0.2 and 1.0 seconds, respectively, with a 2 percent chance of exceedance in 50
years.
Upslope from the east basement retaining walls, short rockery structures are currently planned.
The rockeries should be founded at least 8 feet in horizontal distance from the east basement
retaining wall on medium stiff/dense to hard/dense native silt or sand sediments, or on
structural fill compacted to at least 95 percent of ASTM:D 1557. The slopes above the
rockeries should not exceed 211: IV.
Horizontally backfilled basement walls that are free to yield laterally at least 0.1 percent of
their height may be designed using an equivalent fluid equal to 40 pounds per cubic foot (pcf).
Fully restrained, horizontally backfilled, rigid walls that cannot yield should be designed for an
equivalent fluid of 55 pcf. If parking areas are adjacent to walls, a surcharge equivalent to 2
feet of soil should be added to the wall height in determining lateral design forces.
As required by the 2003 IBC, retaining wall design should include a seismic surcharge
pressure in addition to the equivalent fluid pressures presented above. Considering the site
soils and the recommended wall backfill materials, we recommend a seismic surcharge
pressure of 4H and 8H psf, where H is the wall height in feet for the active and at -rest loading
conditions, respectively. The seismic surcharge should be modeled as a rectangular
distribution with the resultant applied at the midpoint of the wall.
The lateral pressures presented above are based on the conditions of a uniform backfill
consisting of excavated on-site granular (sandy) soils, or imported granular structural fill
compacted to 90 percent of - ASTM:D 1557. A higher degree of compaction is not
recommended, as this will increase the pressure acting on the walls. A lower compaction may
result in settlement of the slab -on -grade or other structures supported above the walls. Thus,
the compaction level is critical and must be tested by our firm during placement. Surcharges
from adjacent footings or heavy construction equipment must be added to the above values.
Lateral loads can be resisted by friction between the foundation and the native, medium
stiff/dense to hard/dense soils or supporting structural fill soils, or by passive earth pressure
acting on the buried portions of the foundations. The foundations must be backfilled with
granular structural fill, compacted to at least 95 percent of the maximum dry density, to
achieve the passive resistance provided below. We recommend the following allowable design
parameters:
• Passive equivalent fluid = 250 pcf
• Coefficient of friction = 0.35
n
r.
Drainage
Perimeter footing drains should be provided for all retaining walls and footings. It is
imperative that proper drainage be provided so that hydrostatic pressures do not develop
against the walls. This would involve installation of a minimum, 1 -foot -wide blanket drain to
within 1 foot of finish grade for the full wall height using imported washed gravel against the
walls. If a drainage mat is used, it should be installed according to the manufacturer's
specifications. The retaining wall detail drawing shown on the building plans we reviewed
included this drain. All footing drains should be tightlined separately from roof drains to an
approved discharge location.
Closure
We trust this information meets your current needs
additional information, please contact us.
Sincerely,
ASSOCIATED EARTH SCIENCES, INC.
Kirkland, Washington
�X
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704
Ge
JonN. S dergaard
Jon N_ Sondergaard, P. G., P. E. G.
Principal Engineering Geologist
Attachments: Figure 1 - Site and Exploration Plan
Exploration Pit Log
JNS/ld
KE060165A 1
Projects1200601651KE1 W P
R
If you have any questions or require
EXPIRES 2 1 b 1 `
Matthew A -Miller, P.E.
Associate Engineer
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Associated Earth Sciences, Inc. SITE AND EXPLORATION PLAN
EDMONDS SHORT PLAT DATE 4106
® ® ® EDMONDS, WASHINGTON PROS. NO. KE0601'65A
LOG OF EXPLORATION PIT NO. EP -1 South Home
N
z Edmonds Short Plat
CU
Edmonds, WA
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Associated Earth Sciences, Inc.
Logged by: SGB Project No. KE05957A
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Approved by: 113106
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This fog is part of the reportprepared by Associated Earth Sciences, Inc. (AESI) for the named project and should be
read together with that report for complete interpretation. This to the location this trench the
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summary applies only of at
time of excavation. Subsurface conditions may change at this location with the passage of time. The data presented are
o
a simpliication of actual conditions encountered.
DESCRIPTION
Topsoil
1
Weathered Soil/Colluvium
2
Loose, very moist, brown, silty SAND with roots, mottled.
Pre -Fraser Deposits
Medium Stitt, very moist, brown, sandy SILT.
3
4
Medium stiff to stiff, very moist, brown, sandy SILT, little gravel.
5
6
Very stiff, moist, gray, sandy SILT, trace gravel and cobbles.
7
8
9
Hard below 9'.
10
11
Bottom of exploration pit at depth 10 feet
Slow seepage at 2'_
12
13
14
15
16
17
18
19
N
z Edmonds Short Plat
CU
Edmonds, WA
IL
Associated Earth Sciences, Inc.
Logged by: SGB Project No. KE05957A
IL
Approved by: 113106
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Min. 16"—I
0 1
0 5
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12"
Firm undisturbed soil
(See Note 2)
No roadway, parking lots
or building footings
in this area
/
' Min.
2_or flatter)
1�
klin. 1' wide layer of 2"-4" quarry
spalls adjacent to rockery
Stable cut face in natural material
(See note 5)
1" (or less) diameter washed gravel
min. 6" cover over pipe,
2" gravel under pipe
Min. 4" diameter perforated
rigid PVC pipe. Min. 1% continuous
slope to outlet
NOTES:
1. Rockeries higher than 5' shall be constructed of rocks of graduated sizes from 5 --man to 2—man,
from bottom to top. Rockeries of 5' or lower shall be constructed of 3—man to 2—man, from
bottom to top.
2. Inspection of subgrade, placement of base course and drainage, and finished rockery by engineer
is required.
3. Rock shall be sound and have a minimum density of 160 pounds per cubic foot.
4. The long dimension of all rocks shall be placed perpendicular to the wall. Each rock should bear on
two rocks in the tier below.
5. Rockeries are erosion—control structures, not retaining walls. Natural material mi
free standing in cut face. Maximum height of 3 feet for rockeries facing fill soil
R Lb. I
Avg. Dimension (In.) ',
L T30284
_
1 -Man 1100-300 I
12 to 18 i
jONAt '
o I 2 -Man 300-800
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18 to 28
28 to 36
3 -Man 800-1500
o 4Man i 1500-2200
_ 36 to 48
EXPIRES 2 /6 I
i 5 -Man 12200-4000 1
a
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48 to 54 J
Associated Earth Sciences, Inc.
UNREINFORCED ROCKERY DETAIL FIGURE 2
DATE 5106
76th AVENUE WEST, LOT 3
® ® ® ® EDMONDS, WASHINGTON
PROJECT N0. KE060165A
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