REPORT 917515 Abbott Residence Report Edmonds.pdfPRELIMINARY GEOTECHNICAL
ENGINEERING EVALUATION
ABBOTT RESIDENCE
16404 75TH PLACE WEST
EDMONDS, WASHINGTON
PREPARED FOR
DEREK ABBOTT
NGA
Main Office
17311— 135t° Ave NE, A-500
Woodinville, WA 98072
(425) 486-1669 • FAX (425) 481-2510
March 27, 2015
Mr. Derek Abbott
221 185th Place SW
Bothell, WA 98012
NELSON GEOTECHNICAL
ASSOCIATES, INC.
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Preliminary Geotechnical Engineering Evaluation
Abbott Residence
16404 75" Place West
Edmonds, Washington
NGA File No. 917515
Dear Mr. Abbott:
Engineering -Geology Branch
5526 Industry Lane, #2
East Wenatchee, WA 98802
(509) 665-7696 • FAX (509) 665-7692
We are pleased to submit the attached report titled "Preliminary Geotechnical Engineering Evaluation —
Abbott Residence—16404-75th Place West — Edmonds, Washington." This report summarizes the
existing surface and subsurface conditions within the project site, and provides geotechnical
recommendations for design and construction of the proposed site improvements. Our services were
completed in general accordance with the proposal signed by you on February 12, 2015.
The site is situated on gently to moderately sloping ground above to the right-of-way for the Burlington
Northern Santa Fe railroad and the shore of Puget Sound. The site is currently occupied by an existing
single-family residence within the upper eastern portion of the property along 75th Place West. We
understand that the proposed development plans consist of removing the existing residence and
constructing a new single-family residence in the approximate location of the current structure. Retaining
walls and shoring systems may be needed to construct the proposed structure into the sloping ground
depending on final proposed elevations. Specific grading, and utility plans were not available at the time
this report was prepared. Stormwater management plans have also not been fmalized at this time, but we
understand that they will likely include tightlining the runoff down to the bottom of the slope or into an
existing storm system within the vicinity of the property. We therefore should be retained to review final
development plans prior to applying for a permit.
The site is mapped as part of the large historic/prehistoric Meadowdale Landslide complex area now
known as the North Edmonds Earth Subsidence & Landslide Hazard Area (ESHLA). The site is located
in the designated "Zone A" within the lower portion of the slide complex. This report provides
information and discussion to fulfill the requirements of the City of Edmonds for construction within this
area.
Based on our site reconnaissance and explorations, and our review of the preliminary plans, we have
concluded that development of a single family residence on this site should be feasible, from a
Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Summary - Page 2
geotechnical standpoint. We did not observe signs of recent deep-seated slope failures or earth
subsidence on the property. The proposed development area appears to be relatively stable under current
conditions. The recommendations presented in this report should aid in maintaining and/or improving the
current stability conditions observed at the site.
Based on the landslide debris and shallow perched groundwater conditions encountered in our
explorations, we recommend supporting the planned residence on a deep foundation system consisting of
drilled augercast piles in order to advance the structure loads through the loose/soft upper soils down to
the more competent native deposits at depth. Specific recommendations for foundation design and
installation are provided in the attached report. In the attached report, we have also provided general
recommendations for site grading, slabs -on -grade, structural fill placement, retaining walls, erosion
control, and drainage. These recommendations are preliminary in nature. We should be retained to
review and comment on final development plans and observe the earthwork phase of construction.
We strongly recommend that all runoff generated within this site, including roof downspouts, driveways,
yard and footing drains, and all runoff entering the property from the road or adjacent properties, be
collected in a tightline and routed to the bottom of the slope or into an approved discharge system. No
water should be infiltrated or dispersed within the site or near the site slopes. Such activity may cause
sliding within the site slopes.
We should be retained to review final grading and drainage plans prior to construction. We also
recommend that NGA be retained to provide monitoring and consultation services during construction to
confirm that the conditions encountered are consistent with those indicated by the explorations, to provide
recommendations for design changes should the conditions revealed during the work differ from those
anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with
contract plans and specifications.
We appreciate the opportunity to provide service to you on this project. Please contact us if you have any
questions regarding this report or require further information.
Sincerely,
NELSON GEOTECHNICAL ASSOCIATES, INC.
cNo-
Khaled
cc: Ron Johnson — Johnson Architects
Table of Contents
INTRODUCTION.......................................................................................................................................................I
SCOPE.......................................................................................................................................................................... I
SITECONDITIONS...................................................................................................................................................2
SURFACECONDITIONS................................................................................................................................................2
SUBSURFACE CONDITIONS.........................................................................................................................................2
HYDROLOGIC CONDITIONS.........................................................................................................................................4
SENSITIVE AREA EVALUATION..........................................................................................................................4
SEISMICHAZARD.......................................................................................................................................................4
EROSIONHAZARD......................................................................................................................................................5
LANDSLIDE HAZARD/SLOPE STABILITY.....................................................................................................................5
CONCLUSIONS AND RECOMMENDATIONS.....................................................................................................6
GENERAL....................................................................................................................................................................
6
EROSION CONTROL AND SLOPE PROTECTION MEASURES
..........................................................................................8
SITE PREPARATION AND GRADING.............................................................................................................................9
TEMPORARY AND PERMANENT SLOPES......................................................................................................................9
DEEPFOUNDATIONS.................................................................................................................................................10
STRUCTURALFILL....................................................................................................................................................12
RETAININGWALLS...................................................................................................................................................13
STRUCTURALSLABS.................................................................................................................................................14
PAVEMENTSUBGRADE.............................................................................................................................................14
SITEDRAINAGE........................................................................................................................................................15
USEOF THIS REPORT...........................................................................................................................................16
LIST OF FIGURES
Figure 1 — Vicinity Map
Figure 2 — Site Plan
Figure 3 — Cross-section A -A'
Figure 4 — Soil Classification Chart
Figure 5 and 6 — Boring Logs
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation
Abbott Residence
16404-75t' Place West
Edmonds, Washington
INTRODUCTION
This report presents the results of our preliminary geotechnical engineering evaluation for the proposed
Abbott Residence project. The address for the site is 16404-75"' Place West in Edmonds, Washington, as
shown on the Vicinity Map in Figure 1. The purpose of the study is to explore and characterize the
surface and subsurface conditions at the site and provide general geotechnical recommendations for site
development. For our use in preparing this report, we have been provided with a boundary and
topographic survey titled "16404 75th Pl. W., Edmonds, WA," dated March 3, 2015, prepared by D.R.
Strong Consulting Engineers.
The site is situated on gently to moderately sloping ground that descends from 75th Place West to the
right-of-way of the Burlington Northern Santa Fe (BNSF) railroad and the shore of Puget Sound. An
existing single-family residence is located within the upper eastern portion of the property along 75th
Place West. Project plans consist of removing the existing residence and constructing a new single-
family residence in the same approximate location of the existing structure. Stormwater plans have not
been finalized at this time, but we anticipate that runoff generated on this site will be tighlined to
discharge at the bottom of the slope or into an existing stormwater system within the vicinity of the
property. The current site layout is shown on the Site Plan in Figure 2.
The site is mapped as part of the large historic/prehistoric Meadowdale Landslide area now known as the
North Edmonds Earth Subsidence & Landslide Hazard Area (ESHLA). Slide movement from the large-
scale slide complex and smaller localized slides within the complex can both affect this property. The
residence design will take this into consideration.
SCOPE
The purpose of this study is to explore and characterize the site surface and subsurface conditions, and
provide opinions and recommendations for the proposed site development. Specifically, our scope of
services includes the following:
1. Review available soil and geologic maps of the area.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation
Abbott Residence
Edmonds, Washington
NGA File No. 917515
March 27, 2015
Page 2
2. Explore the subsurface soil and groundwater conditions within the site with two
approximately 20- to 30-foot deep geotechnical borings using a limited access drill rig.
The drill rig was subcontracted by NGA.
3. Map the conditions on the slope and evaluate current slope stability conditions.
4. Perform laboratory classification and analysis of soil samples, as necessary.
5. Provide recommendations for earthwork, foundation support, and slabs -on -grade in
accordance with the City standards for development in the North Edmonds ESLHA.
6. Provide recommendations for temporary and permanent slopes.
7. Provide recommendation for deep foundation support, as needed.
8. Provide recommendations for residence retaining walls.
9. Provide recommendations for subgrade preparation.
10. Provide recommendations for site drainage and erosion control.
11. Document the results of our findings, conclusions, and recommendations in a written
geotechnical report.
SITE CONDITIONS
Surface Conditions
The site is situated on a gentle to moderate west -facing slope overlooking Puget Sound. The property is
currently occupied by an existing single-family residence within the upper eastern portion of the property
that is planned to be removed as a part of the proposed development plan. The ground surface within the
property slopes gently to moderately down to the west from 75th Place West to the existing railroad tracks
and Puget Sound at gradients in the range of approximately 6 to 27 degrees (II to 51 percent). The
existing site conditions, site topography, and interpreted subsurface conditions are presented on Cross
Sections A -A' in Figure 3.
The site is generally vegetated with grass, landscaping vegetation, and sparse trees. The site is bordered
to the north and south by existing residential properties, to the east by 75th Place West and to the west by
the BNSF railroad tracks and Puget Sound. The existing and proposed site conditions are shown on the
Site Plan in Figure 2.
Subsurface Conditions
Geology: The geologic units for the site vicinity are shown on the Preliminary Geologic Map of the
Edmonds East and Edmonds West Quadrangles, Snohomish and King Counties, Washington, by Mackey
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 3
Smith (U.S.G.S., 1975). The site is mapped as old landslides (Qols) with Whidbey Formation deposits
mapped nearby. The old landslide deposits are described as large slumps that occurred during the
ablation of the Puget Lobe of the Vashon ice sheet by lowering of water -table level. The Whidbey
Formation is described as nonglaical river flood plain deposits consisting of clay, silt, and sand with a few
lenses of small pebbles. We generally encountered landslide debris underlain by clay with silt, and fine
sand that we interpreted as native Whidbey Formation soils.
Explorations: The subsurface conditions within the site were explored on March 5, 2015 by drilling two
borings using a limited -access drill rig to depths of approximately 26.5 to 31.5 feet below the existing
ground surface. The approximate locations of our explorations are shown on the Site Plan in Figure 2. A
geologist from NGA was present during the explorations, examined the soils and geologic conditions
encountered, obtained samples of the different soil types, and maintained logs of the borings.
A Standard Penetration Test (SPT) was performed on each of the samples during drilling to document soil
density at depth. The SPT consists of driving a 2-inch outer -diameter, split -spoon sampler 18 inches
using a 140-pound hammer with a drop of 30 inches. The number of blows required to drive the sampler
the final 12 inches is referred to as the "N" value and is presented on the boring logs. The N value is used
to evaluate the strength and density of the deposit.
The soils were visually classified in general accordance with the Unified Soil Classification System,
presented in Figure 4. The logs of our borings are attached to this report and are presented as Figures 5
and 6. We present a brief summary of the subsurface conditions in the following paragraphs. For a
detailed description of the subsurface conditions, the boring logs should be reviewed.
At the surface of the boring explorations, we encountered approximately 2.5 feet of loose/soft brown -gray
silty fine to medium sand and fine sandy silt with varying amounts of gravel and organics that we
interpreted as undocumented fill soils. Underlying the undocumented fill, we encountered approximately
15.0 to 17.5 feet of very loose/soft to stiff, gray to blue -gray silty fine sand with trace organics and clay
with varying amounts of silt and fine sand that we interpreted as landslide debris. Below the landslide
debris in both borings, we encountered very stiff to hard/dense blue -gray clay with silt and fine sand with
trace silt that we interpreted as native Whidbey Formation deposits. Both of our borings were terminated
within the native Whidbey Formation deposits at depths in the range of approximately 26.5 to 31.5 feet
below the existing ground surface.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 4
Hydrologic Conditions
Groundwater seepage was encountered in both our explorations at approximately 3.5 feet. However, wet
to saturated conditions were encountered sporadically throughout the upper soil horizons. We interpreted
this moisture to be groundwater collecting within sandier/less dense lenses of the subsurface, possibly
generated from upslope. It is our opinion that the groundwater observed within our explorations is
perched water. Perched water occurs when surface water infiltrates through less dense, more permeable
soils and accumulates on top of relatively low permeability materials. The more permeable soils on this
site would consist of the sand seams found within the landslide debris. The low permeability soil consists
of underlying silt. Perched water does not represent a regional groundwater "table" within the upper soil
horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would
expect the amount of perched groundwater to decrease during drier times of the year and increase during
wetter periods. However, due to the large area of recharge, there may be areas of seepage and wet soils
on this site even in the drier times of the year.
SENSITIVE AREA EVALUATION
Seismic Hazard
Older landslide debris and medium stiff to hard cohesive soils were encountered underlying the site.
Based on the 2012 International Building Code (IBC), the site conditions best fit the description for Site
Class E.
Hazards associated with seismic activity include liquefaction potential and amplification of ground
motion by soft or loose geologic deposits. Liquefaction is caused by a rise in pore pressures in a loose,
fine sand deposit beneath the groundwater table. It is our opinion that the medium dense/stiff or better
native soils interpreted to underlie the site have a low potential for liquefaction or amplification of ground
motion; however these materials could experience instability as a result of significant seismic activity.
The competent cohesive soils interpreted to form the core of the site slopes are considered stable with
respect to deep-seated slope failures. However, the overlying loose surficial materials and landslide
debris throughout the site have the potential for shallow sloughing failures during seismic events. Such
events should not affect the planned residence provided our recommendations for foundation support are
incorporated in the project designs.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 5
Erosion Hazard
The criteria used for determining the erosion hazard for the site soils includes soil type, slope gradient,
vegetation cover, and groundwater conditions. The erosion sensitivity is related to the vegetative cover
and the specific surface soil types, which are related to the underlying geologic soil units. The Soil
Survey of Snohomish County Area, Washington, by the Soil Conservation Service (SCS) was reviewed to
determine the erosion hazard of the on -site soils. The site surface soils were classified using the SCS
classification system as Alderwood-Everett gravelly sandy loams, 25 to 70 percent slopes. These soils are
listed as having a moderate hazard of water erosion, and on the steeper portions of the slope the erosion
hazard is considered high. These soils should have a low to moderate hazard for erosion in areas that are
not disturbed and where the vegetation cover is not removed.
Landslide Hazard/Slope Stability
The criteria used for the evaluation of landslide hazards include soil type, slope gradient, and groundwater
conditions. The site slopes gently to moderately down to the west. Groundwater seepage was not
observed on the sloping portions of the property during site visit.
This site and the overall site vicinity lies within an ancient landslide area. The site and vicinity have been
relatively stable for a very long period of time, and development in the area has taken place in the form of
single-family residences, roadways, and underground utilities. Although the likelihood of the ancient
slide to become active in the forseable future is very low, extreme environmental conditions coupled with
inadequate human practices could, in theory, re -activate the ancient landslide. Such external factors could
include severe and elongated weather events and/or significant seismic activity.
The site falls within "Zone A" of the North Edmonds Earth Subsidence and Landslide Hazard Area
Report prepared by Landau Associates for the City of Edmonds. This designation requires that certain
features be included (or excluded) in the design. Such features include the restriction of cuts and fills, the
need for tightlining runoff into an approved system, the need to design foundations and retaining walls to
withstand high lateral earth pressures and potential loss of soil beneath parts of the foundation, the need to
vegetate slopes with deeply rooted drought -tolerant vegetation, and the elimination of any and all
irrigation systems. We have addressed all of these requirements in the remainder of this report.
We encountered what we interpreted as older landslide debris to depths of about 20 feet below the
existing ground surface. Medium dense/stiff undisturbed native soils were encountered below this
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 6
material, which we interpret the core of the slope at depth to consist primarily of this relatively stable
material. Potential deep-seated slide planes were reported to be up to 100 feet deep below ground surface
within the area; however, we did not observe signs of recent deep-seated slope failures on the property
and do not anticipate that such failures will occur during the expected life of the structure. Localized
areas of surface instability and surface sliding can occur on steep slopes, particularly where modified
through grading activities. Backwasting (movement of near -surface soil) through soil erosion processes
or local surface slides is common to slopes, particularly where the soils are exposed to weathering.
Normal surface erosion and shallow sloughing failures should be expected to continue on the steeper
portions of the site, but we have provided geotechnical recommendations for deep -foundation support,
erosion control, and other development considerations that should reduce the potential impact of site
development on the site slopes.
CONCLUSIONS AND RECOMMENDATIONS
General
It is our opinion, from a geotechnical standpoint, that the site should be compatible with the proposed
development of a single-family residence, provided that the geotechnical recommendations presented in
this report are incorporated into project plans and followed during construction. The proposed
development area appears to be relatively stable under current conditions. However, the historic landslide
mapped at the site could be reactivated by extreme natural conditions and/or poor grading and/or drainage
activities within the site and by other human activity in the general site vicinity. We consider this
potential to be extremely low. To alleviate potential site instability concerns, we recommend that the
entire residence be supported on a deep foundation system consisting of augercast piles extending through
the upper landslide debris and terminating into the competent undisturbed soils at depth. This is further
described in the Deep Foundations subsection of this report. We should be retained to review the project
plans prior to applying for a permit, and to monitor earthwork and foundation system installation during
construction
In general, the site currently appears generally stable with respect to deep-seated movement. However,
the site vicinity is mapped within an older landslide complex and our explorations encountered evidence
of past ground movement. The potential for landslide and erosion hazards will depend on how the site is
graded and how surface water and near surface water are controlled. We recommend that site grading be
kept to a minimum and that grading and site drainage plans be subjected to geotechnical engineering
review prior to construction. This review would include specific stability analysis of proposed cuts and
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 7
fills and would provide recommendations for accomplishing the desired grading while maintaining long-
term stability.
Grading plans were not finalized at the time of this report, but we anticipate that cuts may be needed to
allow construction of the residence foundation. If these cuts cannot be sloped back to a safe inclination
due to site constraints, we recommend that the cuts be shored with a soldier pile retaining wall or a similar
system. The need for a shoring system should be determined during final design. This potential wall
could be designed as a permanent wall and incorporated into the residence foundations. We provide
recommendations for temporary and permanent cut slopes in the Temporary and Permanent Slopes
section of this report.
We recommend that if a slab -on -grade is utilized in the lower portions of the proposed residence that the
slab be designed as a structural slab and be supported on the deep foundation system. Other hard
surfaces, such as paved areas or walkways that are supported on the existing soil have some risk of future
settlement, cracking, and the need for maintenance. To reduce this risk, we recommend over -excavating
a minimum of two feet of the upper soil from the slab and pavement areas and replacing this material with
compacted pit run or crushed rock structural fill. This recommendation is only for hard surfaces to be
supported on grade and does not apply for the lower floor structural slab. Even with the recommended
treatment, some settlement of the underlying loose material should be anticipated.
The control of surface and near -surface water is very important for the long-term stability of the site and
on the steeper portions of the site slopes. We highly recommend that temporary and final site grading be
designed to direct surface water away from the structures and away from the site slopes. Final drainage
plans have not been developed at this time, but we understand that all stormwater generated on the site
will be collected in tightlines and transported to the bottom of the slope to the west of the property or into
an existing stromwater system within the vicinity of the property. No water should be infiltrated or
dispersed within the site. We discuss general site drainage in the Site Drainage subsection of this report.
The soils encountered within our explorations are considered extremely moisture sensitive and will
disturb easily when wet. We recommend that construction take place during extended periods of dry
weather if possible. If construction takes place during wet weather, additional expenses and delays
should be expected due to the wet conditions. Additional expenses could include the need to export on -
site soil, the import of clean, granular soil for fill, and the need to place a blanket of rock spalls or crushed
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 8
rock in the construction traffic areas and on exposed subgrades prior to placing structural fill or structural
elements.
In this report, we have also provided recommendations for drainage, erosion control, and other
development considerations intended to reduce the potential impact of development on the site and the
site slopes. We should be retained to review final project plans prior to construction. We also
recommend that NGA be retained to provide monitoring and consultation services during construction to
confirm that the conditions encountered are consistent with those indicated by the explorations, to provide
recommendations for design changes should the conditions revealed during the work differ from those
anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with
contract plans and specifications.
Erosion Control and Slope Protection Measures
The erosion hazard for the on -site soils is considered moderate to high, but the actual hazard will be
dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices
(BMPs) should be used to control erosion. Areas disturbed during construction should be protected from
erosion. Erosion control measures may include diverting surface water away from the stripped or
disturbed areas. Silt fences and/or slope waddles should be erected to prevent muddy water from leaving
the site or flowing over the site slopes. Disturbed areas should be planted as soon as practical and the
vegetation should be maintained until it is established. The erosion potential for areas not stripped of
vegetation should be low to moderate. Also, irrigation systems should not be installed within the
property.
Protection of the site slopes should be performed as required by the City of Edmonds. Specifically, we
recommend that the slopes not be disturbed or modified through placement of any fill or future structures
outside the planned development areas. No additional material of any kind should be placed on any
portion of sloping ground, such as excavation spoils and soil stockpiles. Trees may be cut down and
removed from the slopes as long as a mitigation plan is developed for maintaining slope stability, such as
the replacement of vegetation for erosion protection. A vegetation cover should be preserved on the
slopes. Replacement of vegetation should be performed in accordance with the City of Edmonds code.
Under no circumstances should water be allowed to concentrate on the slopes. Any sloping areas
disturbed during construction should be planted with vegetation as soon as practical to reduce the
potential for erosion.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 9
Site Preparation and Grading
Plans for site grading should be devised such that cuts and fills are kept to a minimum. Site preparation
should consist of excavating the residence footprint down to planned elevations. If shoring walls are
needed to support cut excavations, we recommend that the excavation for the building should only be
attempted after the shoring systems are installed. Site preparation should also consist of stripping any
organic topsoil and/or loose/soft soils in areas that will support foundations, slabs -on -grade, pavement, or
structural fill. The stripped material should not be stockpiled in any area between the top of the slope and
the residence footprint. If the exposed soils are loose/soft, they should be compacted to a non -yielding
condition. Areas observed to pump or weave during compaction should be over -excavated and replaced
with rock spalls. If significant surface water flow is encountered during construction, this flow should be
diverted around areas to be developed and the exposed subgrade maintained in a semi -dry condition. In
wet conditions, the exposed subgrade should not be compacted, as compaction of a wet subgrade may
result in further disturbance of the soils. A layer of crushed rock may be placed over the prepared areas to
protect them from further disturbance.
The site soils are considered extremely moisture sensitive and will disturb easily when wet. We
recommend that earthwork construction take place during periods of extended dry weather, and
suspended during periods of precipitation if possible. If work is to take place during periods of wet
weather, care should be taken during site preparation not to disturb the site soils. This can be
accomplished by utilizing large excavators equipped with smooth buckets and wide tracks to complete
earthwork, and diverting surface and groundwater flow away from the prepared subgrades. Also,
construction traffic should not be allowed on the exposed subgrade. A blanket of rock spalls should be
used in construction access areas if wet conditions are prevalent. The thickness of this rock spall layer
should be based on subgrade performance at the time of construction. For planning purposes, we
recommend a minimum one -foot thick layer of rock spalls.
Temporary and Permanent Slopes
Temporary cut slope stability is a function of many factors, including the type and consistency of soils,
depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open and the
presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate
a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to
maintain safe slope configurations since they are continuously at the job site, able to observe the nature
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 10
and condition of the cut slopes, and able to monitor the subsurface materials and groundwater conditions
encountered.
The following information is provided solely for the benefit of the owner and other design consultants and
should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job
site safety. Job site safety is the sole responsibility of the project contractor.
For planning purposes, we recommend that temporary cuts in the on -site material be no steeper than two
units horizontal to one unit vertical (2H:1V). If groundwater seepage is encountered, we would expect
that flatter inclinations would be necessary. We should be retained to specifically review proposed
geometry for significant cuts planned on this site. We recommend that cut slopes be protected from
erosion. Erosion control measures may include covering cut slopes with plastic sheeting and diverting
surface water runoff away from the top of cut slopes. We do not recommend vertical slopes for cuts
deeper than four feet, if worker access is necessary. We recommend that cut slope heights and
inclinations conform to appropriate OSHA/WISHA regulations.
Permanent cut and fill slopes should be no steeper than 3H:1V. However, flatter inclinations may be
required in areas where loose soils are encountered. Permanent slopes should be covered with erosion
control matting and vegetated. The vegetative cover should be maintained until established. We should
specifically review all plans for grading on this project. We do not recommend placing irrigation systems
near the slopes.
Deep Foundations
Due to the presence of a thick layer of landslide debris, shallow perched groundwater, and caving
conditions encountered in our explorations within the proposed residence area, we recommend that the
entire residence be supported on 16-inch diameter augercast piles extending a minimum of five feet into
competent native soils. Based on our explorations, we recommend that the piles be a minimum of 30 feet
deep below current ground surface to satisfy this requirement. However, depending on the actual depth of
the slide debris at the specific pile locations, some of the piles may need to be extended deeper than 30
feet to achieve the minimum five foot embedment into competent native soils. This can be confirmed in
the field during pile installation.
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Edmonds, Washington Page 11
Augercast piles are installed with a hollow -stem auger advanced to the desired pile depth. After reaching
a minimum recommended penetration into bearing soils, a pressure head is created when grout is pumped
into the hollow stem of the auger before starting auger withdrawal. After the grout head is developed,
withdrawal of the auger is timed to maintain the grout pressure head and avoid intrusion of loose soil into
the sides of the pile excavation or discontinuity or "necking" of the pile. The actual volume of the
concrete pumped into each pile is recorded and compared with the theoretical volume of the pile. Piles
with a ratio of actual to theoretical great volume less than 1.1 should be re -drilled.
The augercast piles should provide the necessary vertical support for the structure as well as some lateral
resistance. The success of this method will depend, in part, on site access for the drill rig and other
equipment needed for pile installation. Obstructed piles should be relocated and/or additional piles
installed. Some discussion on relocation of piles should be made with your structural engineer prior to
start of drilling. It is usually best to make any changes while the drill rig is on site.
For preliminary design, we recommend that the piles extend a minimum of 30 feet below the existing
ground surface and penetrate a minimum of 5 feet into the underlying competent native granular and fine-
grained soils to provide adequate end bearing and friction capacities. The competent native material was
encountered at approximately 20 to 25 feet below the existing ground surface within the proposed
residence area. We present design friction, end bearing, and total axial compression capacities for 16-
inch diameter augercast piles, installed as recommended, in the following table. The friction component
should be used to resist uplift forces only. The provided values do not include the weight of the piles. If
the piles weight will be utilized to resist uplift forces, the buoyant unit weight and adequate safety factors
should be used.
Pile Diameter
(Inches)
Total Pile Depth (Feet)
Design Friction (Tons)
(use only for up lift)
Design End Bearing (Tons)
(pile capacity)
16
30
10
25
Lateral resistance on the piers could be calculated based on an equivalent fluid density of 200 pounds per
cubic foot (pcf) applied to two pile diameters. The upper 20 feet should be neglected for the purpose of
calculating the lateral resistance. If this is not feasible, some of the piles may be battered to provide
lateral resistance. Also passive resistance on competent backfill around grade beams could be utilized.
The upper foot of material should be neglected. We should be retained to review pile design and observe
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 12
augercast pile installation.
Structural Fill
General: Fill placed beneath foundations, pavements, and other settlement -sensitive structures, or behind
retaining walls should be placed as structural fill. Structural fill, by definition, is placed in accordance
with prescribed methods and standards and is monitored by an experienced geotechnical professional or
soils technician. Field monitoring procedures would include the performance of a representative number
of in -place density tests to document the attainment of the desired degree of relative compaction. The
area to receive the fill should be prepared as outlined in the Site Preparation and Grading subsection of
this report. Sloping areas to receive fill should be benched prior to fill placement. The benches should be
level and at least four feet wide.
Materials: Structural fill should consist of a good quality, granular soil, free of organics and other
deleterious material and be well graded to a maximum size of about three inches. All-weather fill should
contain no more than five -percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing
the U.S. 3/4-inch sieve). We do not anticipate placement of significant volumes of structural fill for this
project. The on -site soils consist of moisture -sensitive silty materials and slide debris. We recommend
that the on -site material not be used as structural fill. We should be retained to evaluate the suitability of
proposed structural fill materials at the time of construction.
Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling
should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be
thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas
and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density.
Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557
Compaction Test procedure. The moisture content of the soils to be compacted should be within about
two percent of optimum so that a readily compactable condition exists. It may be necessary to over -
excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All
compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree
of compaction.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 13
Retaining Walls
We understand that retaining walls may be incorporated into project plans. We recommend that retaining
walls be kept as short as possible.
The lateral pressure acting on subsurface retaining walls is dependent on the nature and density of the soil
behind the wall, the amount of lateral wall movement which can occur as backfill is placed, wall drainage
conditions, the inclination of the backfill, and other possible surcharge loads. For walls that are free to
yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be
less than if movement is limited by such factors as wall stiffness or bracing (at -rest condition). We
recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces be designed
using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 40 pcf
for yielding (active condition) walls, and 60 pcf for non -yielding (at -rest condition) walls.
These recommended lateral earth pressures are for a drained granular backfill and are based on the
assumption of a horizontal ground surface behind the wall for a distance of at least the subsurface height
of the wall, and do not account for surcharge loads. Additional lateral earth pressures should be
considered for surcharge loads acting adjacent to subsurface walls and within a distance equal to the
subsurface height of the wall. This would include the effects of surcharges such as traffic loads, floor slab
and foundation loads, slopes, or other surface loads. Also, hydrostatic and buoyant forces should be
included if the walls could not be drained. We could consult with the structural engineer regarding
additional loads on retaining walls during final design, if needed.
All wall backfill should be well compacted; however, care should be taken to prevent the buildup of
excess lateral soil pressures, due to over -compaction of the wall backfill. This can be accomplished by
placing wall backfill in thin loose lifts and compacting it with small, hand -operated compactors within a
distance behind the wall equal to at least one-half the height of the wall. The thickness of the loose lifts
should be reduced to accommodate the lower compactive energy of the hand -operated equipment.
Retaining walls that are part of the residence should be supported on auger -cast piles as described above.
Retaining walls associated with driveway grading and other landscaping plan should be kept under four
feet in height and should be supported on a minimum of two feet of rock spalls to reduce the potential for
differential settlement of the walls. The active pressure on the walls can be resisted by friction on the
bottom of the wall footing and passive resistance on the below -grade portion of the footing. We
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 14
recommend using a design soil bearing pressure of no more than 1,500 pounds per square foot (psf) along
with a friction coefficient and passive resistance values of 0.35 and 200 pcf, respectively. The upper one
foot of material should be neglected when calculating the passive pressure.
Permanent drainage systems should be installed for retaining walls. Recommendations for these systems
are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to
evaluate the proposed wall drain backfill material and drainage system installation.
Structural Slabs
As mentioned earlier, we recommend that if a lower floor slab is utilized, that this slab be designed as a
structural slab fully supported on the deep foundation system. We recommend that slabs be underlain by
at least six inches of free -draining gravel with less than three percent by weight passing the Sieve 4200
for use as a capillary break. We recommend that the capillary break be hydraulically connected to the
footing drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy
plastic sheeting (6-mil minimum), should be placed over the capillary break material. An additional 2-
inch-thick moist sand layer may be used to cover the vapor barrier. This sand layer may be used to
protect the vapor barrier membrane and to aid in curing the concrete; however, this sand layer is optional
and is intended to protect the vapor barrier membrane during construction. Other slabs and hard surfaces
that may be supported on the existing soils should be underlain by a minimum of two feet of railroad
ballast in addition to the capillary break and vapor barrier.
Pavement Subgrade
Pavement subgrade preparation should be completed as recommended in the Site Preparation and
Grading and Structural Fill subsections of this report. Depending on the tolerance to pavement
cracking, we recommend that the upper two feet of the existing material be removed and replaced with
granular structural fill or crushed rock. The pavement subgrade should be proof -rolled with a heavy,
rubber -tired piece of equipment, to identify soft or yielding areas that may require repair prior to placing
any structural fill and prior to placing the pavement base course. We should be retained to observe the
proof -rolling and recommend repairs prior to placement of the asphalt or hard surfaces. The pavement
section should be thickened to further reduce the effects of settlement due to the landslide debris, but
potential long-term cracking should still be expected.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 15
Site Drainage
Surface Drainage: The finished ground surface should be graded such that stormwater is directed to an
appropriate stormwater collection system. Water should not be allowed to collect in any area where
footings, slabs, or retaining walls are to be constructed. Final site grades should allow for drainage away
from the structure and away from the site slopes. We suggest that the finished ground be sloped at a
minimum gradient of three percent, for a distance of at least 10 feet away from the structure and slopes.
Surface water should be collected by permanent catch basins and drain lines, and be discharged into an
appropriate discharge system. Under no circumstances should water be allowed to flow uncontrolled over
the site slopes or excavation walls.
We recommend that all stormwater generated on the site, including roof downspouts, footing drains,
pavement and yard drains, and any water flow from the road, be tightlined to the bottom of the slope to
the west or into an approved system within the vicinity of the property. If the stormwater is tightlined to
the bottom of the slope, we recommend that the pipe should end with a perforated tee section
approximately eight feet long that is capped on both ends and embedded onto a crushed rock pad at the
toe of the slope along the railroad tracks.
Subsurface Drainage: If groundwater is encountered during construction, we recommend that the
contractor slope the bottom of the excavations and collect water into ditches and small sump pits where
the water can be pumped out of the excavations and routed into an appropriate outlet.
We recommend the use of footing drains around the planned structure and behind retaining walls.
Footing drains should be installed at least one -foot below planned finished floor elevation. The drains
should consist of a minimum four -inch -diameter, rigid, slotted or perforated, PVC pipe surrounded by
free -draining material, such as washed rock, wrapped in a filter fabric. We recommend that an 18-inch-
wide zone of clean (less than three -percent fines), granular material be placed along the back of the walls
above the drain. Washed rock is an acceptable drain material, or drainage composite may be used instead.
The free -draining material should extend up the wall to one -foot below the finished surface. The top foot
of backfill should consist of low permeability soil placed over plastic sheeting or building paper to
minimize the migration of surface water or silt into the footing drain. Footing drains should discharge
into tightlines leading to an appropriate collection and discharge point with convenient cleanouts to
prolong the useful life of the drains. Roof drains should not be connected to footing drains.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 917515
Abbott Residence March 27, 2015
Edmonds, Washington Page 16
Roof drains should also be installed around the structure. Roof drains should consist of gutters and
downspouts collecting stormwater runoff from the roof The downspouts should discharge to catch basins
and 4-inch minimum diameter, rigid, PVC tightline pipes. The drains should be directed into catch basins
and then into the controlled drainage system. The footing and roof drains should discharge via
independent (separate) tightlines into catch basins/cleanouts leading to the stormwater system. Surface
water from the driveway and yard areas should also be collected in a catch basin and tightlined separately
to the stormwater system.
USE OF THIS REPORT
NGA has prepared this preliminary report for Mr. Derek Abbott and his agents, for use in the planning
and design of the development planned on this site only. The scope of our work does not include services
related to construction safety precautions and 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. There are possible variations in subsurface conditions between the
explorations and also with time. Our report, conclusions, and interpretations should not be construed as a
warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the
budget and schedule.
We recommend that we be retained to review final project plans and provide consultation regarding
specific structure placement, site grading, foundation support, and drainage. We also recommend that
NGA be retained to provide monitoring and consultation services during construction to confirm that the
conditions encountered are consistent with those indicated by the explorations, to provide
recommendations for design changes should the conditions revealed during the work differ from those
anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with
contract plans and specifications. We should be contacted a minimum of one week prior to construction
activities and could attend pre -construction meetings if requested.
All people who own or occupy homes on or near hillsides should realize that landslide movements are
always a possibility. The landowner should periodically inspect the slope, especially after a winter storm.
If distress is evident, a geotechnical engineer should be contacted for advice on remedial/preventative
measures as soon as possible. The probability that landsliding will occur is substantially reduced by the
proper maintenance of drainage control measures at the site (the runoff from the impervious surfaces
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation
Abbott Residence
Edmonds, Washington
NGA File No. 917515
March 27, 2015
Page 17
should be led to an approved discharge point). Therefore, the homeowner should take responsibility for
performing such maintenance.
Within the limitations of scope, schedule, and budget, our services have been performed in accordance
with generally accepted geotechnical engineering practices in effect in this area at the time this report was
prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are
a means to identify and reduce the inherent risks to the owner.
W
NELSON GEOTECHNICAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation
Abbott Residence
Edmonds, Washington
NGA File No. 917515
March 27, 2015
Page 18
We appreciate the opportunity to provide service to you on this project. If you have any questions or
require further information, please call.
Sincerely,
NELSON GEOTECHNICAL ASSOCIATES, INC.
Lee S. Bellah, LG
Project Geologist
Khaled M. Shawish, PE
Principal
LSB:KMS:cja
Six Figures Attached
NELSON GEOTECHNICAL ASSOCIATES, INC.
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Project Number NELSON GEOTECHNICAL No. Date Revision By CK
917515 Abbott Residence NGA ASSOCIATES, INC. 1 3/10/15 Original DPN TSB
a
Vicinity Map GEOTECHNICAL ENGINEERS & GEOLOGISTS
Figure 1 17311-135th Ave. NE, A-500 Snohomish County (425) 339-1669 Z
Woodinville, WA 98072 Wenatchee/Chelan (509) 665-7696
(425) 486-1669 / Fax 481-2510 .neleengeotech.con, O
N
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Site Plan
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391� N � LEGEND
o — — Property line
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o _ _ Number and approximate
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< location of boring 0 40 80
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Z
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Z Q 40 14 8 `a— 40
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> r 33
in (n
to 0
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n
> m
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(n m 0 0
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0 40 80 120 160 200 240 280 320
r Distance (feet)
Exploration
w o
m Boring Designation--> B-1
O 23
23 <-- SPT N-value
y Groundwater Level ---> 1 23
During Exploration 23
23
o W Geologic Contact -->
z (approximate)
cn W x Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure
rniort Fnlrio-M 76-15 Ahhntt P—irlanra Frlmnnr1sM-frinn\RR rhmn
NOTES:
1) Stratigraphic conditions are interpolated between
the explorations. Actual conditions may vary.
2) Elevations are approximate.
UNIFIED SOIL CLASSIFICATION SYSTEM
GROUP
MAJOR DIVISIONS
GROUP NAME
SYMBOL
CLEAN
GW
WELL -GRADED, FINE TO COARSE GRAVEL
COARSE-
GRAVEL
GRAVEL
GP
POORLY -GRADED GRAVEL
GRAINED
MORE THAN 50 %
GRAVEL
GM
SILTY GRAVEL
OF COARSE FRACTION
RETAINED ON
SOILS
NO.4 SIEVE
WITH FINES
GC
CLAYEY GRAVEL
SAND
CLEAN
SW
WELL -GRADED SAND, FINE TO COARSE SAND
SAND
SP
POORLY GRADED SAND
MORE THAN 50 %
RETAINED ON
MORE THAN 50 %
NO. 200 SIEVE
OF COARSE FRACTION
SAND
SM
SILTY SAND
PASSES NO. 4 SIEVE
WITH FINES
Sc
CLAYEY SAND
FINE -
SILT AND CLAY
MIL
SILT
INORGANIC
GRAINED
LIQUID LIMIT
CL
CLAY
LESS THAN 50 %
SOILS
ORGANIC
OL
ORGANIC SILT, ORGANIC CLAY
SILT AND CLAY
MH
SILT OF HIGH PLASTICITY, ELASTIC SILT
INORGANIC
MORE THAN 50 %
PASSES
LIQUID LIMIT
CH
CLAY OF HIGH PLASTICITY, FLAT CLAY
NO. 200 SIEVE
50 % OR MORE
ORGANIC
OH
ORGANIC CLAY, ORGANIC SILT
HIGHLY ORGANIC SOILS
PT
PEAT
NOTES:
1) Field classification is based on visual SOIL MOISTURE MODIFIERS:
examination of soil in general
accordance with ASTM D 2488-93. Dry - Absence of moisture, dusty, dry to
the touch
2) Soil classification using laboratory tests
is based on ASTM D 2488-93. Moist - Damp, but no visible water.
3) Descriptions of soil density or Wet - Visible free water or saturated,
consistency are based on usually soil is obtained from
interpretation of blowcount data, below water table
visual appearance of soils, and/or
test data.
Project Number
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
917515
Abbott Residence
Soil Classification Chart
NGA ASSOCIATES, INC.
GEOTECHNICAL ENGINEERS & GEOLOGISTS
1
3/10/15
Original
DPN
LSB
Figure 4
17311-135th Ave. NE, A-500 Snohomish County (425) 337-1669
Woodinville, WA 98072
Wenatchee/Chelan (509) 665-7696
(425) 486-16691 Fax 481-2510 www.nelsongeotech.com
BORING LOG
B-1
Approximate Ground Surface Elevation: —60 ft
Soil Profile
Sample Data
Penetration Resistance
- 0)
10 20 30 40 50 50+
()
c(Blows/foot
Piezometer
Installation -
`—'
i
Ground Water
Description
Q 0
J
Q o
o f
3
O
n °
E co
Moisture Content
(Percent - ■)
o
Data
@
O
CO U
L
o
(Depth in Feet)
(�
cn
in
10 20 30 40 50 50+
p
J
Dark brown -gray, fine sandy silt with trace organics and
4
iron -oxide staining (soft, moist) F( ILL)
3
'
1
Dark gray, silty fine sand with trace organics and
iron -oxide staining (very loose, wet)
-no iron -oxide staining
=
4
-with interbedded fine sand and silt seams
Gray silt with fine sand and trace organics
(soft, wet to saturated)
ML
19
'
Dark brown silt (very stiff, moist)
ML
3
' 10
...................................................
10
Gray clay with silt and trace slickensides (soft, wet)
-becomes stiff, moist
8
'
CL
15
15
...................................................
15
16
'Blue
and gray clay with silt (very stiff, moist)
-becomes stiff
10
' 20
...................................................
20
11
,
CL
14
' 25
...................................................
25
LEGEND ❑ Solid PVC Pipe L• Concrete M Moisture Content
0 Slotted PVC Pipe Bentonite A Atterberg Limits
Depth Driven and Amount Recovered G Grain -size Analysis
with 2-inch O.D. Split -Spoon Sampler Monument/ Cap ® Native Soil IDS Direct Shear
to Piezometer PP Pocket Penetrometer Readings, tons/ft
Depth Driven and Amount Recovered ❑ Silica Sand
p �r Liquid Limit P Sample Pushed
with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial
NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily
representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log.
Project Number
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
917515
Abbott Residence
NGA ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
17311-135th Ave. NE, A-500 Snohomish County (425) 339-1669
Wenel�Whenelsongeotechmm7696
WaodiPage
1
3/10/15
Original
DPN
LSB
Figure 5
n
1 of 2
(425) 486-1669 1 Fax 4881-2510
BORING LOG
B-1 (cont.)
Soil Profile
Sample Data
Penetration Resistance
()
c
(Blows/foot - 0)
10 20 30 40 50 50+
Z,
Piezometer
Installation -
`—'
i
Ground Water
Description
Q
Q o
3
n °
Moisture Content
MitCtt
o
Data
@ J
o;
O o
In U
E m
0
(Percent - ■)
o
(Depth in Feet)
(�
U)
'0
10 20 30 40 50 50+
-p
J
Gray, fine sand with trace silt (dense, moist)
Sp
33
Boring terminated below existing grade at 31.5 feet on
3/5/15. Groundwater seepage was encountered at 3.5
feet during drilling
35
...................................................
35
40
....................................................
40
45
....................................................
45
50
....................................................
50
55
....................................................
55
LEGEND Solid PVC Pipe Concrete M Moisture Content
Slotted PVC Pipe Bentonite A Atterberg Limits
Depth Driven and Amount Recovered G Grain -size Analysis
with 2-inch O.D. Split -Spoon Sampler Monument/ Cap ® Native Soil IDS Direct Shear
to Piezometer PP Pocket Penetrometer Readings, tons/ft
Depth Driven and Amount Recovered 0 Silica Sand
p �r Liquid Limit P Sample Pushed
with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial
NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily
representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log.
Project Number
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
917515
Abbott Residence
NVGA ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
17311-135th Ave. NE, A-500 Snohomish County (425) 339-1669
Wenel�Whenelsongeotechmm7696
WaodiPage
1
3/10/15
Original
DPN
LSB
Figure 5
n n
2 of 2
(425) 486-1669 1 Fax 4881-2510
BORING LOG
B-2
Approximate Ground Surface Elevation: -72 ft
Soil Profile
Sample Data
Penetration Resistance
- ■)
10 20 30 40 50 50+
t)
c(Blows/foot
Piezometer
Installation -
`-'
i
Ground Water
Description
Q 0
J
Q o
o E
3
n °
E m
Moisture Content
(Percent - ■)
o
Data
@
o
m U
r
0
o
(Depth in Feet)
c�
U)
in
10 20 30 40 50 50+
p
J
Brown -gray, silty fine to medium sand with gravel, trace
6
organics, and iron -oxide staining (loose, moist)
SM
Gray, fine sandy silt with trace organics and iron -oxide
staining (soft, wet)
3
'
=
ML
-----------------
Blue -gray, silty fine sand with trace organics, interbedded
.:.; ..`-
—
5
....................................................
5
silt and silt chunks (very loose, saturated)
—
2
SM
2
'
— — — — — — — — — — —
Blue-gray clay with silt and trace fine sand with
— — ---
10
-
10
interbedded silty fine sand seams (medium stiff, moist)
6
'
CL
— — — — — — — — — — — — — — —
Blue -gray clay with silt (stiff, moist)
— —
—
15
........
...........................................
15
11
'
-becomes very stiff
CL
17
' 20
...................................................
20
25
...................................................
25
-becomes hard
41
Boring terminated below existing grade at 26.5 feet on
3/5/15. Groundwater seepage was encountered at 3.0
feet during drilling
LEGEND ❑ Solid PVC Pipe E� Concrete M Moisture Content
0 Slotted PVC Pipe Bentonite A Atterberg Limits
Depth Driven and Amount Recovered G Grain -size Analysis
with 2-inch O.D. Split -Spoon Sampler Monument/ Cap ® Native Soil IDS Direct Shear
to Piezometer PP Pocket Penetrometer Readings, tons/ft
Depth Driven and Amount Recovered ❑ Silica Sand
p �r Liquid Limit P Sample Pushed
with 3-inch Shelby Tube Sampler + Plastic Limit 1 Water Level T Triaxial
NOTE: Subsurface conditions depicted represent our observations at the time and location of this exploratory hole, modified by engineering tests, analysis and judgement. They are not necessarily
representative of other times and locations. We cannot accept responsibility for the use or interpretation by others of information presented on this log.
Project Number
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
917515
Abbott Residence
NGA ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
17311-135th Ave. NE, A-500 Snohomish County (425) 339-1669
94812510 Wenatchee/Chelan
1
3/10/15
Original
DPN
LSB
Figure 6
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