19-233 834 Walnut St GeoRpt.pdf
________________________________________________
3213 Eastlake Ave E, Ste B
Seattle, WA 98102
Tel (206) 262-0370
Fax (206) 262-0374
Geotechnical & Earthquake
Engineering Consultants
July 29, 2019
Project No. 19-233
Ms. Nina Franey
Edge Design & Build
2107 NW 201st Street
Shoreline, WA 98177
Subject: Geotechnical Engineering Report
Proposed Stairway and Retaining Wall Improvements
834 Walnut Street, Edmonds, Washington
Dear Ms. Franey,
As requested, PanGEO Inc. (PanGEO) completed a geotechnical engineering study to assist the
design team for the proposed stairway and retaining wall improvements located at 834 Walnut
Street in the City of Edmonds, Washington. This study was performed in general accordance
with our mutually agreed scope of work outlined in our proposal dated July 12, 2019, and
subsequently approved by you on July 15, 2019. Our service scope included reviewing readily
available geologic and geotechnical data, excavating three hand borings, conducting a site
reconnaissance, performing engineering analysis, and developing the conclusions and
recommendations presented in this report.
SITE AND PROJECT DESCRIPTION
The project site is located at 834 Walnut Street in the City of Edmonds, Washington (see Figure
1, Vicinity Map). The subject property is an approximately 7,085 square foot, rectangular-shaped
lot. It is bordered to the north by Walnut Street, and to the other three sides by existing single-
family residences. The site is currently occupied by a one-story house with a daylight basement.
The site grade generally slopes down from east to west with an average gradient of about 15
percent (see Plates 1 and 2).
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
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Plate 1. View of the existing stairway and rockery on the
northeast corner of the house, looking south from Walnut
Street.
Plate 2. View of the east side yard above the stairway,
looking south from northeast corner of the house.
We understand that you plan to remodel the interior of the house. We also understand that, as
part of the remodel project, the concrete stairway and modular block wall located to the northeast
corner of the house will be reconstructed. A new entry is also planned that will include new
footings. We anticipate that temporary excavations for the proposed improvements will be up to
about 4 feet deep. According to the City of Edmonds GIS maps, the site is within an erosion and
landslide geologic hazards area.
The conclusions and recommendations outlined in this report are based on our understanding of
the proposed improvements, which is in turn based on the project information provided to us. If
the above project description is substantially different from your proposed improvements, or if
the project scope changes, PanGEO should be consulted to review the recommendations
contained in this study and make modifications, if needed.
SITE GEOLOGY
Based on a review of the Composite Geologic Map of the Sno-King Area (Booth, et al. 2004) the
primary geologic unit in the vicinity of the site is Advance Outwash (Map Unit Qva). Advance
Outwash consists of a silt and sand soil unit deposited by meltwater streams emerging from an
advancing glacier.
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Page 3
SUBSURFACE EXPLORATION AND CONDITIONS
SUBSURFACE EXPLORATION
Our subsurface exploration for the current study consisted of excavating three hand borings (HB-
1 through HB-3) at the site on July 17, 2019, using a hand auger. The approximate hand boring
locations were taped in the field from on-site features, and are plotted on Figure 2. The hand
borings were excavated to depths ranging from about 2½ to 7 feet below the existing grade.
SOIL
The hand borings advanced at the site generally encountered about 3 feet of loose fill overlying
medium dense to dense sand (Advance Outwash). The soils encountered in the hand borings are
generally consistent with the mapped geology at the site. The following is a brief description of
the soils encountered in the test borings drilled at the site. Please refer to the summary hand
boring logs in Appendix A for additional details.
UNIT 1: Fill – This unit was encountered in all three hand borings. The fill encountered
generally consisted of loose sand with rounded to angular gravel and cobbles, and trace
silt. This soil unit extended to about 3 feet below the existing ground surface in HB-1 and
HB-3, respectively, and to the refusal depth of 2½ feet in HB-2.
UNIT 2: Advance Outwash (Qva) – Below the fill, HB-1 and HB-3 encountered
medium dense to dense, fine to medium sand with trace silt, that extended to the
termination depth of 7 and 5 feet in HB-1 and HB-3, respectively. This unit was not
encountered in HB-2. We interpreted this unit as mapped Advance Outwash deposits.
GROUNDWATER
Groundwater was not observed in the hand borings within the depths excavated during our field
exploration. It should be noted that groundwater elevations and seepage rates are likely to vary
depending on the season, tidal fluctuation, local subsurface conditions, and other factors.
Groundwater levels and seepage rates are normally highest during the winter and early spring
(typically October through May).
PREVIOUS SUBSURFACE EXPLORATION
As a part of our study, we also reviewed readily available previous geotechnical explorations in
the site vicinity. Specifically, the following previous exploration was reviewed:
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
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• Logs of Hand Holes (HH-1 and HH-2), 842 Walnut Street, Edmonds, Washington (The
Galli Group, 2007).
The previous hand holes were excavated on the adjacent property to the east. The hand holes
encountered sand with silt and gravel, and bearing soil was encountered at about 1 and 2 feet in
HH-1 and HH-2, respectively. In general, the results of the previous exploration are consistent
with our current subsurface exploration. The previous geotechnical report is included as
Appendix B for reference.
Based on review of the previous hand holes and our experience in the area, the soil conditions
are relatively uniform in the project area.
GEOLOGICALLY HAZARDOUS AREAS ASSESSMENT
Based on a review of the City of Edmonds GIS map and the Edmonds Community Development
Code (ECDC), the subject site is within a Geologically Hazardous Area for erosion and landslide
hazards. The rockery and the slopes above it along the east side of the driveway and east
property line is considered as a steep slope (greater than 40% slope).
LANDSLIDE HAZARDS EVALUATION
Based on review of the topographic survey map provided to us and our field observations, the
site generally slopes down from the east to the west with an average slope gradient of about 15
percent. However, the rockery and slopes above the rockery along the east side of driveway,
which is approximately 12 feet in height, appear to meet the steep slope definition (40% or
greater slopes). Based on the soil data on the east adjacent site and presence of the rockery, it is
our opinion that this steep slope is the result of the previous grading due to street and site
development. It is also our opinion that the risk for the potential future landslide is considered
low, and the site is not considered as a landslide hazard area.
A site reconnaissance of the subject property was conducted on July 17, 2019. During our site
reconnaissance, we did not observe obvious evidence of past slope instability or ground
movement at the subject site. Based on our field observations and the results of subsurface data
at the subject site and adjacent property to the east, in our opinion, the subject site appears to be
globally stable in its current configuration. Furthermore, it is our opinion that the proposed
stairway and wall improvements as currently planned is feasible from a geotechnical engineering
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Page 5
standpoint. It is our further opinion that the proposed improvements as currently planned will not
adversely affect the overall stability of the site or adjacent properties, provided the
recommendations outlined herein are followed and the proposed development is properly
designed and constructed.
EROSION HAZARDS EVALUATION
According to USDA Soil Conservation Service Map, the site soil is the Alderwood Urban land
complex. Based on the soils encountered in the hand borings and site topography, the near-
surface site soils are anticipated to exhibit slight to moderate erosion potential. However, due to
very minor ground disturbance and excavations planned, in our opinion, the potential erosion
hazards at the site can be effectively mitigated with the best management practice during
construction and with properly designed and implemented landscaping for permanent erosion
control. During construction, the temporary erosion hazard can be effectively managed with an
appropriate erosion and sediment control plan, including but not limited to installing silt fence
at the construction perimeter, limiting removal of vegetation to the construction area, placing
rocks or hay bales at the disturbed/traffic areas and on the downhill side of the project, covering
stockpile soil or cut slopes with plastic sheets, constructing a temporary drainage pond to
control surface runoff and sediment trap if needed, placing rocks at the construction entrance,
etc. Permanent erosion control measures should include establishing vegetation, landscape
plants, and hardscape established at the end of project.
23.80.060 DEVELOPMENT STANDARDS – GENERAL REQUIREMENTS
According to ECDC 23.80.060, alterations of geologically hazardous areas or associated buffers
may only occur for activities that:
1. Will not increase the threat of the geological hazard to adjacent properties beyond
predevelopment conditions;
2. Will not adversely impact other critical areas;
3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to
or less than predevelopment conditions; and
4. Are certified as safe as designed and under anticipated conditions by a qualified engineer
or geologist, licensed in the state of Washington.
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Page 6
Based on the site subsurface information and our understanding of the current plans, it is our
opinion that the proposed project meets the above conditions, and will not have adverse impacts
to the subject and surrounding properties during and after construction, provided that project is
constructed in accordance with the approved plans and commonly accepted practice.
23.80.070 DEVELOPMENT STANDARDS – SPECIFIC HAZARDS
The subject site is considered an erosion hazard area. However, based on the soil conditions and
proposed improvements, it is our opinion that building setback and buffer distance are not
required for the currently proposed improvements. ECDC 23.80.070 states that alterations of an
erosion or landslide area hazard area, minimum building setback and/or buffer may only occur
for activities for which a hazards analysis is submitted and certifies that:
a. The alteration will not increase surface water discharge or sedimentation to adjacent
properties beyond predevelopment conditions;
b. The alteration will not decrease slope stability on adjacent properties; and
c. Such alterations will not adversely impact other critical areas.
In our opinion, the proposed stairway and wall improvements as currently planned meet the
above conditions.
GEOLOGIC HAZARDS MITIGATIONS
Based on the results of our evaluation of the potential geologic hazards at the site, it is our
opinion that no specific mitigation, other than the erosion measure discussed above, is required
for the proposed improvements.
GEOTECHNICAL DESIGN RECOMMENDATIONS
SEISMIC DESIGN PARAMETERS
The Table 1 on page 7 provides seismic design parameters for the site that are in conformance
with the 2015 edition of the International Building Code (IBC), which specifies a design
earthquake having a 2% probability of occurrence in 50 years (return interval of 2,475 years),
and the 2015 USGS seismic hazard maps. The spectral response accelerations were obtained
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
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from the USGS Earthquake Hazards Program Interpolated Probabilistic Ground Motion website
(2008 data) for the project latitude and longitude.
Table 1 – 2015 IBC Seismic Design Parameters
Site
Class
Spectral
Acceleration
at 0.2 sec. (g)
SS
Spectral
Acceleration at
1.0 sec. (g)
S1
Site
Coefficients
Design Spectral
Response
Parameters
Fa Fv SDS SD1
D 1.269 0.497 1.00 1.50 0.846 0.498
FOUNDATIONS
Based on the planned stairway, retaining wall, and entry footing elevations, it is our opinion that
the proposed improvements may be supported on conventional footings bearing on the
undisturbed native sand or compacted structural fill placed on the native sand. The foundation
soils should be compacted to a firm/dense condition.
Soil Bearing Pressure
We recommend that an allowable soil bearing pressure of 2,000 pounds per square foot (psf) be
used to size the new footings. The recommended allowable bearing pressure is for dead plus live
loads. For allowable stress design, the recommended bearing pressure may be increased by one-
third for transient loading, such as wind or seismic forces. Continuous and individual spread
footings should have minimum widths of 18 and 24 inches, respectively.
In designing the footings, the shape of footings will need to be considered in regard to the
available space for temporary excavations. Where space may be limited for an unsupported open
cut, it may be necessary to use L-shaped perimeter footings in order to conserve space and to
allow the temporary excavations to be made within the property limits.
Foundation Performance
Footings designed and constructed in accordance with the above recommendations should
experience total settlement of less than one inch and differential settlement of about ½ inch.
Most of the anticipated settlement should occur during construction as dead loads are applied.
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Page 8
Lateral Resistance
Lateral loads on the structures may be resisted by passive earth pressure developed against the
embedded faces of the foundation system and by frictional resistance between the bottom of the
foundation and the supporting subgrade soils. For footings bearing on the firm native soil or
compacted sand/structural fill, a frictional coefficient of 0.3 may be used to evaluate sliding
resistance developed between the concrete and the compacted subgrade soil. Passive soil
resistance may be calculated using an equivalent fluid weight of 250 pcf, assuming properly
compacted structural fill will be placed against the footings. The above values include a factor of
safety of 1.5. Unless covered by pavements or slabs, the passive resistance in the upper 12 inches
of soil should be neglected.
Footing Excavation and Subgrade Preparation
All footing subgrade should be carefully prepared. The footing subgrade should be compacted to
a dense and unyielding condition prior to concrete pour. Depending on the footing subgrade,
foundation over-excavation may be needed to remove the existing fill and disturbed outwash
sand.
Any loose/soft footing subgrade soil or subgrade soil that cannot be compacted to a dense
condition should be removed from the footing subgrade and backfilled with lean-mix concrete,
Control Density Fill (CDF) or structural fill. Foundation excavations and subgrade conditions
should be observed by PanGEO to confirm that the exposed subgrade is consistent with the
expected conditions and adequate to support the proposed building.
CONCRETE SLAB-ON-GRADE
Conventional slab-on-grade concrete floors, if needed, may be used for this project. We
recommend that floor slabs be supported on the recompacted sand or structural fill placed on
recompacted on-site sand. If loose or soft soils are encountered at the slab subgrade elevation
that cannot be adequately compacted, the loose or soft soil should be over-excavated to
competent native and replaced with compacted structural fill, such as WSDOT Gravel Borrow or
approved equivalent.
The concrete slab-on-grade floors should be underlain by at least 4 inches of capillary break,
which consists of free-draining, clean crushed rock or well-graded gravel compacted to a firm
and unyielding condition. The capillary break material should have no more than 20 percent
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
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passing the No. 4 sieve and less than 5 percent by weight of the material passing the U.S.
Standard No. 100 sieve. We also recommend that a minimum 10-mil polyethylene vapor barrier
be placed below the proposed basement slab.
RETAINING AND BASEMENT WALL DESIGN PARAMETERS
Retaining and basement walls should be properly designed to resist the lateral earth pressures
exerted by the soils behind the wall. Proper drainage provisions should also be provided behind
the walls to intercept and remove groundwater that may be present behind the walls. Our
geotechnical recommendations for the design and construction of the retaining/basement walls
are presented below.
Lateral Earth Pressures
Concrete cantilever walls should be designed for an equivalent fluid pressure of 35 pcf for level
backfills behind the walls assuming the walls are free to rotate. If walls are to be restrained at the
top from free movement, such as basement walls, equivalent fluid pressures of 45 pcf should be
used for level backfills behind the walls. Walls with a maximum 2H:1V backslope should be
designed for an active and at rest earth pressure of 45 and 55 pcf, respectively.
Permanent walls should be designed for an additional uniform lateral pressure of 7H psf for
seismic loading, where H corresponds to the buried depth of the wall. The recommended lateral
pressures assume that the backfill behind the wall consists of a free draining and properly
compacted fill with adequate drainage provisions.
Surcharge
Surcharge loads, where present, should also be included in the design of retaining walls. We
recommend that a lateral load coefficient of 0.3 be used to compute the lateral pressure on the
wall face resulting from surcharge loads located within a horizontal distance of one-half wall
height.
Lateral Resistance
Lateral forces from seismic loading and unbalanced lateral earth pressures may be resisted by a
combination of passive earth pressures acting against the embedded portions of the foundations
and by friction acting on the base of the foundations. Passive resistance values may be
determined using an equivalent fluid weight of 250 pcf. This value includes a factor of safety of
1.5, assuming the footing is poured against dense native sand, re-compacted on-site sandy soil or
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Page 10
properly compacted structural fill adjacent to the sides of footing. A friction coefficient of 0.3
may be used to determine the frictional resistance at the base of the footings. The coefficient
includes a factor safety of 1.5.
Wall Drainage
Provisions for wall drainage should consist of a 4-inch diameter perforated drainpipe behind and
at the base of the wall footings, embedded in 12 to 18 inches of clean crushed rock and pea
gravel wrapped with a layer of filter fabric. Where applicable, in-lieu of conventional footing
drains, weep holes (2” diameter of 10 feet on center) may be used for site retaining walls. A
minimum 18-inch wide zone of free draining granular soils (i.e. pea gravel or washed rock) is
recommended to be placed adjacent to the wall for the full height of the wall. Alternatively, a
composite drainage material, such as Miradrain 6000, may be used in lieu of the clean crushed
rock or pea gravel. The drainpipe at the base of the wall should be graded to direct wat er to a
suitable outlet.
Wall Backfill
In our opinion, the clean sand at the site may be used as wall backfill, provided it can be
compacted to a dense condition. Imported wall backfill, if needed, should consist of free draining
granular material, such as WSDOT Gravel Borrow. In areas where the space is limited between
the wall and the face of excavation, pea gravel or clean crushed rock may be used as backfill
without compaction.
Wall backfill should be moisture conditioned to within about 3 percent of optimum moisture
content, placed in loose, horizontal lifts less than 8 inches in thickness, and systematically
compacted to a dense and relatively unyielding condition and to at least 95 percent of the
maximum dry density, as determined using test method ASTM D 1557. Within 5 feet of the
wall, the backfill should be compacted with hand-operated equipment to at least 90 percent of
the maximum dry density.
CONSTRUCTION CONSIDERATIONS
SITE PREPARATION
Site preparation for the proposed project includes removing existing stairway, stripping and
clearing of surface vegetation and excavations to the design subgrade. All stripped surface
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
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materials should be properly disposed off-site or be “wasted” on site in non-structural landscaping
areas.
Following site clearing and excavations, the adequacy of the subgrade where structural fill,
foundations, slabs, or pavements are to be placed should be verified by a representative of PanGEO.
The subgrade soil in the improvement areas, if recompacted and still yielding, should also be over-
excavated and replaced with compacted structural fill or CDF/lean-mix concrete.
TEMPORARY EXCAVATIONS
As currently planned, the proposed construction will require excavations up to 4 feet below the
existing grade. We anticipate the excavations to mainly encounter loose to dense sand. All
temporary excavations should be performed in accordance with Part N of WAC (Washington
Administrative Code) 296-155. The contractor is responsible for maintaining safe excavation
slopes and/or shoring.
All temporary excavations deeper than a total of 4 feet should be sloped or shored. Based on the
soil conditions at the site, for planning purposes, it is our opinion that temporary excavations for
the proposed construction may be sloped 1H:1V (Horizontal:Vertical) or flatter. Based on our
current understanding of the anticipated building layout and finished floor elevation, it appears
that sufficient space is available for unsupported open cuts. Where space may be limited, the use
of L-shaped footings may be required to conserve space for the temporary cuts. In event that
sufficient space is not available for unsupported open cuts, temporary shoring will be needed to
support the temporary excavations.
The temporary excavations and cut slopes should be re-evaluated in the field during construction
based on actual observed soil conditions, and may need to be flattered in the wet seasons and
should be covered with plastic sheets. We also recommend that heavy construction equipment,
building materials, excavated soil, and vehicular traffic should not be allowed within a distance
equal to 1/3 the slope height from the top of any excavation.
MATERIAL REUSE
In the context of this report, structural fill is defined as compacted fill placed under footings,
concrete stairs and landings, and slabs, or other load-bearing areas. In our opinion, the on-site
sand is poorly graded and will be difficult to compact to a dense condition. As such, on-site sand
is not suitable to be used as structural fill, but can be used as wall backfill and general fill in the
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Page 12
non-structural areas. Structural fill, if needed, should consist of imported, well-graded, granular
material, such as WSDOT Gravel Borrow, or approved equivalent. Well-graded recycled
concrete may also be considered as a source of structural fill. Use of recycled concrete as
structural fill should be approved by the geotechnical engineer. If use of the on-site soil is
planned, the excavated soil should be stockpiled and protected with plastic sheeting to prevent
softening from rainfall in the wet season.
STRUCTURAL FILL PLACEMENT AND COMPACTION
Structural fill should be moisture conditioned to within about 3 percent of optimum moisture
content, placed in loose, horizontal lifts less than 8 inches in thickness, and systematically
compacted to a dense and relatively unyielding condition and to at least 95 percent of the
maximum dry density, as determined using test method ASTM D 1557.
Depending on the type of compaction equipment used and depending on the type of fill material,
it may be necessary to decrease the thickness of each lift in order to achieve adequate
compaction. PanGEO can provide additional recommendations regarding structural fill and
compaction during construction.
WET WEATHER EARTHWORK
In our opinion, the proposed site construction may be accomplished during wet weather (such as
in winter) without adversely affecting the site stability. However, earthwork construction
performed during the drier summer months likely will be more economical. Winter construction
will require the implementation of best management erosion and sedimentation control practices
to reduce the chance of off-site sediment transport. Some of the site soils contain a high
percentage of fines and are moisture sensitive. Any footing subgrade soils that become softened
either by disturbance or rainfall should be removed and replaced with structural fill, Controlled
Density Fill (CDF), or lean-mix concrete. General recommendations relative to earthwork
performed in wet conditions are presented below:
• Site stripping, excavation and subgrade preparation should be followed promptly by the
placement and compaction of clean structural fill or CDF;
• The size and type of construction equipment used may have to be limited to prevent soil
disturbance;
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
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• The ground surface within the construction area should be graded to promote run-off of
surface water and to prevent the ponding of water;
• Geotextile silt fences should be strategically located to control erosion and the movement
of soil;
• Structural fill should consist of less than 5% fines; and
• Excavation slopes should be covered with plastic sheets.
SURFACE DRAINAGE AND EROSION CONSIDERATIONS
Surface runoff can be controlled during construction by careful grading practices. Typically, this
includes the construction of shallow, upgrade perimeter ditches or low earthen berms in
conjunction with silt fences to collect runoff and prevent water from entering excavations or to
prevent runoff from the construction area from leaving the immediate work site. Temporary
erosion control may require the use of hay bales on the downhill side of the project to prevent
water from leaving the site and potential storm water detention to trap sand and silt before the
water is discharged to a suitable outlet. All collected water should be directed under control to a
positive and permanent discharge system.
Permanent control of surface water should be incorporated in the final grading design. Adequate
surface gradients and drainage systems should be incorporated into the design such that surface
runoff is directed away from structures. Potential problems associated with erosion may also be
reduced by establishing vegetation within disturbed areas immediately following grading
operations.
ADDITIONAL SERVICES
To confirm that our recommendations are properly incorporated into the design and construction
of the proposed addition, PanGEO should be retained to conduct a review of the final project
plans and specifications, and to monitor the construction of geotechnical elements. The City of
Edmonds, as part of the permitting process, will also require geotechnical construction
inspection services. PanGEO can provide you a cost estimate for construction monitoring
services at a later date.
We anticipate that the following additional services will be required:
• Review final project plans and specifications
• Verify implementation of erosion control measures;
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
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• Verify soil bearing;
• Confirm the adequacy of the compaction of structural backfill; and
• Other consultation as may be required during construction.
Modifications to our recommendations presented in this report may be necessary, based on the
actual conditions encountered during construction.
CLOSURE
We have prepared this report for Ms. Nina Franey and the project design team.
Recommendations contained in this report are based on a site reconnaissance, a subsurface
exploration program, review of pertinent subsurface information, and our understanding of the
project. The study was performed using a mutually agreed-upon scope of work.
Variations in soil conditions may exist between the locations of the explorations and the actual
conditions underlying the site. The nature and extent of soil variations may not be evident until
construction occurs. If any soil conditions are encountered at the site that are different from those
described in this report, we should be notified immediately to review the applicability of our
recommendations. Additionally, we should also be notified to review the applicability of our
recommendations if there are any changes in the project scope.
The scope of our work does not include services related to construction safety precautions. Our
recommendations are not intended to direct the contractors’ methods, techniques, sequences or
procedures, except as specifically described in our report for consideration in design.
Additionally, the scope of our work specifically excludes the assessment of environmental
characteristics, particularly those involving hazardous substances. We are not mold consultants
nor are our recommendations to be interpreted as being preventative of mold development. A
mold specialist should be consulted for all mold-related issues.
This report has been prepared for planning and design purposes for specific application to the
proposed project in accordance with the generally accepted standards of local practice at the time
this report was written. No warranty, express or implied, is made.
This report may be used only by the client and for the purposes stated, within a reasonable time
from its issuance. Land use, site conditions (both off and on-site), or other factors including
advances in our understanding of applied science, may change over time and could materially
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
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affect our findings. Therefore, this report should not be relied upon after 24 months from its
issuance. PanGEO should be notified if the project is delayed by more than 24 months from the
date of this report so that we may review the applicability of our conclusions considering the
time lapse.
It is the client’s responsibility to see that all parties to this project, including the designer,
contractor, subcontractors, etc., are made aware of this report in its entirety. The use of
information contained in this report for bidding purposes should be done at the contractor’s
option and risk. Any party other than the client who wishes to use this report shall notify
PanGEO of such intended use and for permission to copy this report. Based on the intended use
of the report, PanGEO may require that additional work be performed and that an updated report
be reissued. Noncompliance with any of these requirements will release PanGEO from any
liability resulting from the use this report.
We appreciate the opportunity to be of service.
Sincerely,
7/29/2019
John A. Manke, L.G. H. Michael Xue, P.E.
Staff Geologist Senior Geotechnical Engineer
Attachments:
Figure 1 Vicinity Map
Figure 2 Site and Exploration Plan
Appendix A – Summary Hand Boring Logs
Figure A-1 Terms and Symbols for Boring and Test Pit Logs
Figure A-2 Log of Hand Boring HB-1
Figure A-3 Log of Hand Boring HB-2
Figure A-4 Log of Hand Boring HB-3
Appendix B – Previous Geotechnical Report by The Galli Group
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Page 16
REFERENCES
Booth, D.B., Cox, B.F., Troost, K.G., and Shimel, S.A., 2004, Composite Geologic Map of the
Sno-King Area, Central Puget Lowland, Washington, Seattle- Area Geologic Mapping
Project (SGMP), University of Washington, and the United States Geological Survey
(USGS), Scale 1:24,000.
International Code Council, 2015, International Building Code.
The Galli Group, 2007, Geotechnical Reconnaissance, Proposed Deck Addition, 842 Walnut
Street, Edmonds, Washington.
United States Geological Survey, Earthquake Hazards Program, Interpolated Probabalisitic
Ground Motion for the Conterminous 48 States by Latitude and Longitude, 2008 Data,
accessed via: http://earthquake.usgs.gov/designmaps/us/application.php
WSDOT, 2016, Standard Specifications for Road, Bridge and Municipal Construction, M 41-10,
Washington State Department of Transportation.
Proposed Stairway and
Retaining Wall Improvements
834 Walnut Street
Edmonds, WA
VICINITY MAP
19-233 1
Reference: Google Terrain MapNot to Scale
Project Site
Figure No.Project No.19-233
Proposed Stairway and
Retaining Wall Improvements
834 Walnut Street
Edmonds, Washington 2
SITE AND EXPLORATION PLAN
Approx. Scale
1" = 20'
HB-1
HB-2
HB-3
Approx. Hand Boring Locations
Legend:
Note: Base map modified from Topographic Survey
prepared by Crones Surveying, dated May 27, 2019.
APPENDIX A
SUMMARY HAND BORING LOGS
MOISTURE CONTENT
2-inch OD Split Spoon, SPT
(140-lb. hammer, 30" drop)
3.25-inch OD Spilt Spoon
(300-lb hammer, 30" drop)
Non-standard penetration
test (see boring log for details)
Thin wall (Shelby) tube
Grab
Rock core
Vane Shear
Dusty, dry to the touch
Damp but no visible water
Visible free water
Terms and Symbols for
Boring and Test Pit Logs
Density
SILT / CLAY
GRAVEL (<5% fines)
GRAVEL (>12% fines)
SAND (<5% fines)
SAND (>12% fines)
Liquid Limit < 50
Liquid Limit > 50
Breaks along defined planes
Fracture planes that are polished or glossy
Angular soil lumps that resist breakdown
Soil that is broken and mixed
Less than one per foot
More than one per foot
Angle between bedding plane and a planenormal to core axis
Very Loose
Loose
Med. Dense
Dense
Very Dense
SPT
N-values
Approx. Undrained Shear
Strength (psf)
<4
4 to 10
10 to 30
30 to 50
>50
<2
2 to 4
4 to 8
8 to 15
15 to 30
>30
SPT
N-values
Units of material distinguished by color and/orcomposition from material units above and below
Layers of soil typically 0.05 to 1mm thick, max. 1 cm
Layer of soil that pinches out laterally
Alternating layers of differing soil material
Erratic, discontinuous deposit of limited extent
Soil with uniform color and composition throughout
Approx. Relative
Density (%)
Gravel
Layered:
Laminated:
Lens:
Interlayered:
Pocket:
Homogeneous:
Highly Organic Soils
#4 to #10 sieve (4.5 to 2.0 mm)
#10 to #40 sieve (2.0 to 0.42 mm)
#40 to #200 sieve (0.42 to 0.074 mm)
0.074 to 0.002 mm
<0.002 mm
UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS GROUP DESCRIPTIONS
Notes:
MONITORING WELL
<15
15 - 35
35 - 65
65 - 85
85 - 100
GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MH
CH
OH
PT
TEST SYMBOLS
50%or more passing #200 sieve
Groundwater Level at time of drilling (ATD)Static Groundwater Level
Cement / Concrete Seal
Bentonite grout / seal
Silica sand backfill
Slotted tip
Slough
<250
250 - 500
500 - 1000
1000 - 2000
2000 - 4000
>4000
RELATIVE DENSITY / CONSISTENCY
Fissured:
Slickensided:
Blocky:
Disrupted:
Scattered:
Numerous:
BCN:
COMPONENT DEFINITIONS
Dry
Moist
Wet
1. Soil exploration logs contain material descriptions based on visual observation and field tests using a systemmodified from the Uniform Soil Classification System (USCS). Where necessary laboratory tests have beenconducted (as noted in the "Other Tests" column), unit descriptions may include a classification. Please refer to thediscussions in the report text for a more complete description of the subsurface conditions.
2. The graphic symbols given above are not inclusive of all symbols that may appear on the borehole logs.Other symbols may be used where field observations indicated mixed soil constituents or dual constituent materials.
COMPONENT SIZE / SIEVE RANGE COMPONENT SIZE / SIEVE RANGE
SYMBOLS
Sample/In Situ test types and intervals
Silt and Clay
Consistency
SAND / GRAVEL
Very Soft
Soft
Med. Stiff
Stiff
Very Stiff
Hard
Phone: 206.262.0370
Bottom of BoringBoulder:
Cobbles:
Gravel
Coarse Gravel:
Fine Gravel:
Sand
Coarse Sand:
Medium Sand:
Fine Sand:
Silt
Clay
> 12 inches
3 to 12 inches
3 to 3/4 inches
3/4 inches to #4 sieve
Figure A-1
Atterberg Limit Test
Compaction Tests
Consolidation
Dry Density
Direct Shear
Fines Content
Grain Size
Permeability
Pocket Penetrometer
R-value
Specific Gravity
Torvane
Triaxial Compression
Unconfined Compression
Sand
50% or more of the coarse
fraction passing the #4 sieve.
Use dual symbols (eg. SP-SM)
for 5% to 12% fines.
for In Situ and Laboratory Testslisted in "Other Tests" column.
50% or more of the coarse
fraction retained on the #4
sieve. Use dual symbols (eg.
GP-GM) for 5% to 12% fines.
DESCRIPTIONS OF SOIL STRUCTURES
Well-graded GRAVEL
Poorly-graded GRAVEL
Silty GRAVEL
Clayey GRAVEL
Well-graded SAND
Poorly-graded SAND
Silty SAND
Clayey SAND
SILT
Lean CLAY
Organic SILT or CLAY
Elastic SILT
Fat CLAY
Organic SILT or CLAY
PEAT
ATT
Comp
Con
DD
DS
%F
GS
Perm
PP
R
SG
TV
TXC
UCC
LO
G
K
E
Y
1
3
-
1
0
4
_
L
O
G
S
.
G
P
J
P
A
N
G
E
O
.
G
D
T
6
/
1
8
/
1
3
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Figure A-2
Figure A-2: Summary Log of Hand Boring HB-1
Approximate ground surface elevation: 253 feet
Depth (ft) Material Description
0 – 3
Unit 1: Loose, brown, fine to medium SAND; occasional roots with rounded
and angular gravel and cobbles; moist (Fill)
- Rounded and angular gravel and cobbles from surface to 1½ feet
- Trace gravel below 1½ feet
3 – 7
Unit 2: Medium dense, light brown, fine to medium SAND with silt and trace
gravel; moist (Advance Outwash)
- Becomes dense at 5 feet
Notes:
1. HB-1 was terminated at 7 feet below ground surface.
2. Groundwater was not observed in the hand boring.
Plate 1: Cuttings from about 4 feet below surface in HB-1.
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Figure A-3
Figure A-3: Summary Log of Hand Boring HB-2
Approximate ground surface elevation: 253 feet
Depth (ft) Material Description
0 – 2½
Unit 1: Loose, light brown, fine to medium SAND; occasional roots with
rounded and angular gravel and cobbles; dry (Fill)
- Becomes moist at 1¾ feet
Notes:
3. HB-1 was terminated at 2½ feet below ground surface due to refusal on gravel/cobbles.
4. Groundwater was not observed in the hand boring.
Plate 1: Cuttings from about 1½ feet below surface in HB-2.
Ms. Nina Franey
Proposed Stairway and Retaining Wall Improvements – 834 Walnut Street, Edmonds, WA
July 29, 2019
19-233 834 Walnut St GeoRpt PanGEO, Inc. Figure A-4
Figure A-4: Summary Log of Hand Boring HB-3
Approximate ground surface elevation: 253 feet
Depth (ft) Material Description
0 – 3
Unit 1: Loose, brown, fine to medium SAND; with rounded and angular
gravel and cobbles; moist (Fill)
- Rounded and angular gravel and cobbles from surface to 2 feet
- Trace gravel below 2 feet
3 – 5
Unit 2: Medium dense, light brown, fine to medium SAND with silt and
trace gravel; moist (Advance Outwash)
- Becomes dense at 5 feet
Notes:
5. HB-1 was terminated at 5 feet below ground surface.
6. Groundwater was not observed in the hand boring.
Plate 1: Cuttings from about 3 feet below surface in HB-3.
APPENDIX B
Previous Geotechnical Report
by The Galli Group