REVIEWED BLD2021-1665+Geotech Report+12.14.2021_3.01.26_PM+2572485NELSON GEOTECHNICAL
ASSOCIATES. INC.
December 10, 2021
Terianne Brubaker
VIA Email: tbrubaker@walkerconstructioninc.com
Geotechnical Engineering Evaluation
Brubaker Residence Settlement Evaluation
9712 — 242"d Place SW
Edmonds, Washington
NGA File No. 1313321
Dear Terianne:
17311-1351" Ave. N.E. Suite A-500
Woodinville, WA 98072
(425) 486-1669
www.nelsongeotech.com
We are pleased to submit the attached report titled "Geotechnical Engineering Evaluation — Brubaker
Residence Settlement Evaluation— 9712 — 242"d Place SW — Edmonds, Washington." This report
summarizes our observations of the existing surface and subsurface conditions within the site and
provides general recommendations for the proposed residence stabilization. Our services were
completed in general accordance with the proposal signed by you on October 18, 2021.
The subject property consists of a keystone -shaped parcel occupied by a single-family residence built in
1968. Vegetation within the site consists of grass -covered yard areas and scattered young to mature
trees. Topography within the site slopes gently to the southwest in the northeastern portion, becoming
moderately to steeply sloping to the southwest in the southwestern backyard.
We visited the property on October 13, 2021 to observe existing conditions and again on November 8,
2021 to preform two drilled borings with a limited access drill rig. We observed indications of settlement
within the driveway and several cracks in the foundation stem wall on the northwestern portion of the
residence. Our explorations indicated that the site was underlain by up to 13.0 feet of surficial
topsoil/undocumented fill underlain by competent advanced outwash soils at depth. We understand
you are working with structural engineering consultants to develop stabilization plans consisting of pin
pile support.
It is our opinion that the observed settlement is likely the result of ongoing consolidation within the
loose undocumented fill soils interpreted to underly the foundations of the main residence structure.
We recommend that the main residence foundations be supported with pin piles extending into the
competent native bearing soils that underlie the site at depth. these soils should generally be
encountered approximately 9.0 to 13.0 feet below the existing ground surface, based on our
explorations. However, deeper areas of loose soils or undocumented fill could be encountered in
unexplored areas of the site.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Brubaker Residence Settlement Evaluation
Edmonds, Washington
NGA File No. 1313321
December 10, 2021
Summary— Page 2
In the attached report, we have also provided general recommendations for pin pile installation,
temporary and permanent slopes, utilities, subgrade preparation, erosion control, and drainage. We
should be retained to review and comment on final settlement repair plans and observe the earthwork
phase of 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 differ from those anticipated, and to evaluate whether or not earthwork and pin
pile installation activities comply with contract plans and specifications.
It has been a pleasure 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.
11IMPH
Khaled M. Shawish, PE
Principal Engineer
NELSON GEOTECHNICAL ASSOCIATES, INC.
TABLE OF CONTENTS
INTRODUCTION............................................................................................................1
SCOPE...........................................................................................................................1
SITECONDITIONS......................................................................................................... 2
SurfaceConditions...................................................................................................... 2
Subsurface Conditions................................................................................................2
Hydrogeologic Conditions........................................................................................... 3
SENSITIVE AREA EVALUATION...................................................................................... 3
SeismicHazard............................................................................................................ 3
ErosionHazard...........................................................................................................4
Landslide hazard/Slope Stability.................................................................................4
CONCLUSIONS AND RECOMMENDATIONS....................................................................5
General....................................................................................................................... 5
ErosionControl........................................................................................................... 6
Site Preparation and Grading..................................................................................... 6
Temporary and Permanent Slopes............................................................................. 7
Foundation Underpinning Improvements.................................................................. 8
StructuralFill..............................................................................................................9
Pavements................................................................................................................10
Utilities.....................................................................................................................10
SiteDrainage............................................................................................................11
CONSTRUCTION MONITORING...................................................................................11
USE OF THIS REPORT..................................................................................................12
LIST OF FIGURES
Figure 1— Vicinity Map
Figure 2 — Schematic Site Plan
Figure 3 — Cross -Section A -A'
Figure 4 — Soil Classification Chart
Figures 5 and 6 — Boring Logs
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Brubaker Residence Settlement Evaluation
9712 — 242nd Place SW
Edmonds, Washington
INTRODUCTION
This report presents the results of our geotechnical engineering evaluation of settlement related distress
within the residence structure located at 9712 — 242nd Place SW, as shown on the Vicinity Map in Figure
1. The parcel number for the subject property is 004503-000-011-00. The purpose of this study is to
explore and characterize the site's surface and subsurface conditions and to provide geotechnical
recommendations to mitigate the settlement observed within the residence.
The site consists of a keystone -shaped parcel covering approximately 0.22 acres. The site is currently
occupied by an existing single-family residence. Topographically, the site slopes gently to the southwest
in the northeastern portion, becoming moderately to steeply sloping to the southwest in the
southwestern backyard. We understand that the existing residence has recently experienced noticeable
settlement and you are working with structural engineering consultants to develop stabilization plans
consisting of pin pile support. Our services have been requested to determine the cause of settlement,
as well as provide considerations for the proposed repair. The existing site layout and the location of our
explorations is shown on the Site Plan in Figure 2.
SCOPE
The purpose of this study is to explore and characterize the site surface and subsurface conditions and
provide our opinion regarding the ongoing settlement issues.
Specifically, our scope of services included the following:
1. Reviewing available soil and geologic maps of the area.
2. Exploring the subsurface soil and groundwater conditions within the proposed
development areas with up to two, 25-foot deep geotechnical boreholes using a limited -
access drill rig. Drilling services were subcontracted by NGA.
3. Mapping the conditions on the site slopes using shallow, hand -tool explorations where
necessary to construct geological cross sections and qualitatively evaluate slope
stability.
4. Performing laboratory grain -size sieve analysis on soil samples, as necessary.
5. Providing our opinion on the cause of structure settlement.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1313321
Brubaker Residence Settlement Evaluation December 10, 2021
Edmonds, Washington Page 2
6. Providing recommendations for earthwork and foundation support, including 'pin pile'
underpinning.
7. Providing recommendations for temporary and permanent slopes.
8. Providing recommendations for subsurface utilities and pavement subgrade
preparation.
9. Providing general recommendations for site drainage and erosion control.
10. Documenting the results of our findings, conclusions, and recommendations in a written
geotechnical report.
SITE CONDITIONS
Surface Conditions
The site consists of a keystone -shaped parcel covering approximately 0.22 acres. The site is currently
occupied by a single-family residence. The property is bordered by 242"d Place SW to the northeast, and
neighboring residential properties on all other sides. Topographically the site slopes gently to the
southwest in the northeastern portion, becoming moderately to steeply sloping to the southwest in the
southwestern backyard. Vegetation within the site consists of grass -covered yard areas and scattered
young to mature trees. We did not observe surface water within the site during our site reconnaissance
on October 13, 2021 or during our explorations on November 8, 2021.
Subsurface Conditions
Geology: The geologic units for this site are shown on Geologic Map of the Edmonds East and Part of the
Edmonds West Quadrangles, Washington, by Minard, J.P. (USGS, 1983). The site is mapped as Advanced
outwash (Qva). Advanced outwash is described as glacially compacted, mostly clean, pebbly sand with
varying amounts of gravel and cobbles with localized iron oxide staining. Our explorations typically
encountered fill soils underlain by dense gray, fine to coarse sand with varying amounts of gravel, silt,
and iron oxide staining consistent with the description of advanced outwash at depth.
Explorations: The subsurface conditions within the site were explored on November 8, 2021 by drilling
two geotechnical boreholes with a limited access drill rig. Explorations extended to approximate depths
26.5 feet below the existing ground surface using a limited access drill rig. 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 test pits.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Brubaker Residence Settlement Evaluation
Edmonds, Washington
NGA File No. 1313321
December 10, 2021
Page 3
The soils were visually classified in general accordance with the Unified Soil Classification System,
presented in Figure 4. The logs of our explorations 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 paragraph.
For a detailed description of the subsurface conditions, the logs of the test pits should be reviewed.
At the surface of Borehole One and Two we generally encountered approximately 9.0 to 13.0 feet of
light brown, fine to medium sand with gravel, silt, and organics which we interpreted as undocumented
fill soils. Underlying the topsoil and/or undocumented fill soils we generally encountered gray, fine to
coarse sand with silt and gravel that we interpreted as advanced outwash deposits to the depths
explored. Boreholes One and Two were terminated within native glacial outwash deposits at a depth of
26.5 feet below the existing ground surface.
Hydrogeologic Conditions
We did not encounter groundwater seepage in any of the explorations. If groundwater is encountered
during construction, we would interpret this as 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 consist of the topsoil/weathered soils and
undocumented fill. The low permeability soil consists of relatively silty native deposits. 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.
SENSITIVE AREA EVALUATION
Seismic Hazard
We reviewed the 2018 International Building Code (IBC) for seismic site classification for this project.
Since bedrock is inferred to underlie the site at depth, the site conditions best fit the IBC description
for Site Class B.
Table 1 below provides seismic design parameters for the site that are in conformance with the
2018 IBC, which specifies a design earthquake having a two percent probability of occurrence in 50
years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1313321
Brubaker Residence Settlement Evaluation December 10, 2021
Edmonds, Washington Page 4
Table 1— 2018 IBC Seismic Design Parameters
Site Class
Spectral Acceleration
Spectral Acceleration
Site Coefficients
Design Spectral
at 0.2 sec. (g)
at 1.0 sec. (g)
Response
S,
S1
Parameters
Fa
Fv
Sos
Sol
B
1.261
0.493
1.000
1.507
0.841
0.496
The spectral response accelerations were obtained from the USGS Earthquake Hazards Program
Interpolated Probabilistic Ground Motion website (2008 data) for the project latitude and longitude.
Hazards associated with seismic activity include liquefaction potential and amplification of ground
motion. 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 bedrock interpreted to underlie the site has a low potential
for liquefaction or amplification of ground motion.
Erosion Hazard
The criteria used for determination of erosion hazard areas include 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 Natural Resources Conservation Service (NRCS), was
reviewed to determine the erosion hazard of the on -site soils. The site surface soils were classified using
the NRCS classification system as Everett very gravelly sandy loam, 0 to 8 percent slopes. The erosion
hazard for these soils is not listed. However, it is our opinion that the erosion hazard should be low to
moderate in areas with vegetated, undisturbed soil.
Landslide Hazard/Slope Stability
The criteria used for evaluation of landslide hazards includes soil type, slope gradient, and groundwater
conditions. A moderate southwest -facing slope descends from the back of the existing residence down
toward neighboring residence at gradients of up to 35 degrees (70 percent) as shown on Cross- Section
A -A' in Figure 3. The overall vertical relief of site slopes is estimated to be approximately 16-feet. We
did not observe indications of deep-seated slope movement or erosion during our site visit. We also did
not observe any groundwater seepage emitting from the face of the steep slope during our site visit.
Our explorations and observations indicate that the core of the slope consists primarily of competent
bedrock. It is our opinion that while there is potential for erosion, soil creep, and shallow failures within
the loose surficial soils on the slope, there is not a significant potential for deep-seated slope failure
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1313321
Brubaker Residence Settlement Evaluation December 10, 2021
Edmonds, Washington Page 5
under current site conditions. Proper site grading and drainage as well as stabilization techniques as
recommended in this report should help maintain current stability conditions.
CONCLUSIONS AND RECOMMENDATIONS
General
Based on our explorations, observations, and understanding of the existing site conditions, it is our
opinion that the settlement and distress to the residence foundations may be a direct result of on -going
consolidation of undocumented fill soils in the range of approximately 9.0- and 13.0-feet underlying the
ground surface along the northwestern portion of the residence. Undocumented fill soils on site will
likely continue to experience consolidation and subsidence under the current loads, and at an increased
rate as a result of an earthquake or significant rainfall, which could lead to more distress and settlement
to the structure and foundation system. Signs of settlement are present along the northwestern
foundation lines and within the driveway on the northern side of the site. Ultimately, to stabilize the
residence structure and stop further settlement, we recommend the main load bearing foundation
elements within the house be underpinned with 2-inch diameter steel pipe piles. This includes exterior
and interior foundations. This is further discussed in the Foundation Underpinning subsection of this
report. We should review underpinning plans prior to implementation.
Your structural engineer should determine the extent of foundation areas to be underpinned and overall
layout of the underpinning system. Portions of the residence structure may be able to be re -leveled
during construction under the direction of the structural engineer and the contractor. It is likely that
portions of the structure not currently showing signs of distress may also be underlain by the loose fill
material encountered in our explorations. Under this scenario, underpinning only the currently
distressed portions of the residence may create a situation where the remaining portions of the
structure may start to settle shortly after the distressed portions are underpinned. We recommend that
after the recommended underpinning is completed, the structure be monitored for any signs of further
distress, and additional pin piles or anchors installed if signs of further distress are observed.
In addition to the foundation improvements, we recommend that the drainage system surrounding the
residence be investigated and improved, as necessary. Such improvements should include confirming
the placement and functionality of footing drains around the structure foundation and routing all
downspouts and runoff from all hard surfaces into a permanent discharge system.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1313321
Brubaker Residence Settlement Evaluation December 10, 2021
Edmonds, Washington Page 6
Erosion Control
The erosion hazard for the on -site soils is interpreted to be slight to moderate for exposed soils, but
actual erosion potential 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 straw bales should be
erected to prevent muddy water from leaving the site. We also recommend that any soil stockpiles and
excavation walls be covered with plastic sheeting and not placed near site slopes. The erosion potential
of areas not disturbed should be low.
Site Preparation and Grading
We anticipate grading activities associated with the foundation repairs to be minimal; however, other
hardscape improvements may require more significant excavation. After erosion control measures are
implemented, site preparation should consist of stripping any topsoil, undocumented fill, and loose soils
from new slab and pavement areas, and other structural areas, to expose medium dense or better
native bearing soils. The stripped soil should be removed from the site or stockpiled for later use as a
landscaping fill.
After stripping, if the exposed subgrade is deemed loose, it should be compacted to a non -yielding
condition and then proof -rolled with a heavy rubber -tired piece of equipment. Areas observed to pump
or weave during the proof -roll test should be reworked to structural fill specifications or over -excavated
and replaced with properly compacted structural fill or rock spalls. If loose soils are encountered in the
new slab or pavement areas, the loose soils should be removed and replaced with rock spalls or granular
structural fill. If significant surface water flow is encountered during construction, this flow should be
diverted around areas to be developed, and the exposed subgrades should be maintained in a semi -dry
condition.
Alternatively, due to the significant depths of undocumented fill soils varying from approximately 9.0-
feet in the northwest corner of the property to approximately 13.0-feet in the southwest corner of the
residence we recommend subgrades for any proposed pavement or hardscape features could be
improved by overexcavating a minimum of 12-inches of loose undocumented fill soils, compacting the
resulting subgrade to a firm and unyielding condition and replacing with granular structural fill soils. The
overexcavated subgrade should be carefully evaluated and if loose areas are encountered, they should
be additionally overexcavated and replaced with quarry spalls or similar structural fill materials. The
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1313321
Brubaker Residence Settlement Evaluation December 10, 2021
Edmonds, Washington Page 7
above recommended near surface improvements should greatly reduce the potential for future
settlement but will not eliminate the potential altogether.
If wet conditions are encountered, alternative site stripping and grading techniques might be necessary.
These could include using large excavators equipped with wide tracks and a smooth bucket to complete
site grading and covering exposed subgrade with a layer of crushed rock for protection. If wet conditions
are encountered or construction is attempted in wet weather, the subgrade should not be compacted as
this could cause further subgrade disturbance. In wet conditions, it may be necessary to cover the
exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive
soils from disturbance by machine or foot traffic during construction. The prepared subgrade should be
protected from construction traffic and surface water should be diverted around areas of prepared
subgrade.
The site soils are considered to be moisture -sensitive and will disturb easily when wet. We recommend
that construction take place during the drier summer months if possible. However, if construction takes
place during the wet season, additional expenses and delays should be expected due to the wet
conditions. Additional expenses could include the need for placing a blanket of rock spalls on exposed
subgrades, construction traffic areas, and paved areas prior to placing structural fill. Wet weather
grading will also require additional erosion control and site drainage measures. Some of the on -site soils
may be suitable for use as structural fill, depending on the moisture content of the soil at the time of
construction. NGA should be retained to evaluate the suitability of all on -site and imported structural fill
material during construction. We should stress that all temporary excavations associated with the
removal of the existing residence and pool should comply with safe cut inclinations as described in the
following section.
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 at all times as indicated in OSHA guidelines for cut slopes.
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.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1313321
Brubaker Residence Settlement Evaluation December 10, 2021
Edmonds, Washington Page 8
For planning purposes, we recommend that temporary cuts in the upper undocumented fill soils be no
steeper than 2 Horizontal to 1 Vertical (2H:1V). Temporary cuts in the competent native soils at depth
should be no steeper than 1.5H:1V. If significant groundwater seepage or surface water flow were
encountered, we would expect that flatter inclinations would be necessary. We recommend that cut
slopes be protected from erosion. The slope protection measures may include covering cut slopes with
plastic sheeting and diverting surface 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 2H:1V. However, flatter inclinations may be
required in areas where loose soils are encountered. Permanent slopes should be vegetated and the
vegetative cover maintained until established.
Foundation Underpinning Improvements
We recommend that the main residence foundations be supported on a deep foundation system to
transfer structure loads down into the underlying competent native bearing materials to limit future
settlement and damage to the structure. Structural brackets should be used to attach the pin piles to
the existing foundations. The structural engineer should design the new foundation supports and
determine the location of the supports based on the recommendations provided in this report. A
qualified contractor specializing in foundation retrofit should be retained to complete the repairs.
Considering the limited site access conditions, it is our opinion that the most feasible foundation
underpinning systems are 2-inch diameter pin piles driven to refusal using a hand operated 140-pound
jackhammer. Extreme care should be taken during the proposed repairs as to not impact existing
utilities within the vicinity of the residence.
Our explorations encountered loose undocumented fills within the planned areas to be repaired. If
large objects or debris are present within the fill, there is a possibility that this material may obstruct
some piles or anchors at shallow depths. There should be contingencies in the budget and design for
additional/relocated piles/anchors that may be obstructed by possible debris in the fill. We recommend
that utilities within the near vicinity to the proposed repairs should be verified by the contractor and
measurements made in the field at the time of underpinning installation to ensure the underpinning
elements do not encounter the existing foundations or any underground utilities. Test piles may need
to be driven along the lower downslope side of the structure to confirm the approach prior to finalizing
the overall underpinning design.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Brubaker Residence Settlement Evaluation
Edmonds, Washington
NGA File No. 1313321
December 10, 2021
Page 9
Due to the rigid pile support, friction between the foundation and subgrade soil should not be
considered for resisting lateral pressures on this structure. Also, passive resistance acting on the below -
grade portion of the residence foundations may be used to resist lateral pressures. If additional lateral
restraint is required due to the slightly sloping ground surface battered piles may be utilized. The
project structural engineer should determine the need for additional lateral restraint.
We should be retained to review final plans and to monitor installation of the pin piles during
construction.
For 2-inch diameter pipe piles driven to refusal using a hand-held, 140-pound jackhammer, we
recommend a design axial compression capacity of three tons for each pile. The refusal criterion for this
pile and hammer size is defined as less than one inch of movement during 60 seconds of continuous
driving. We recommend using galvanized extra strong (Schedule 80) steel pipe for the 2-inch pin piles.
Final pile depths should be expected to vary somewhat and will depend on the depth of the loose
material, the nature of the underlying competent soils. For preliminary design the pin piles should
penetrate a minimum of ten feet into the competent native glacial soils below the fill material in order
to develop the design capacity. Based on our explorations, we anticipate overall pile depths on the
order of 19 - to 23-feet; however, this depth is an estimate based on relative soil density and native soil
elevation and will likely vary depending on the specific soil conditions at each location. Piles that refuse
within the upper undocumented fill soils should be rejected and replacement piles should be driven
after consulting with the structural engineer regarding the new pile locations. The piles should be
spaced a minimum of two feet apart to avoid a grouping effect on the piles. We should also be retained
to observe pin pile installation during construction and verify refusal depths.
Structural Fill
General: We do not anticipate significant structural fill placement for this project; however, fill placed
beneath foundations, pavement, or other settlement -sensitive structures 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 suitably
prepared to a firm, non -yielding condition prior to fill placement as described below.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Brubaker Residence Settlement Evaluation
Edmonds, Washington
NGA File No. 1313321
December 10, 2021
Page 10
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). The site soils are not suitable for use as structural fill. We should be
retained to evaluate all proposed structural fill material prior to placement.
Fill Placement: Following excavation to final subgrade, placement of structural fill may proceed. All fill
placements 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 and should be tested
Pavements
New pavement subgrade preparation and structural filling where required, should be completed as
recommended in the Site Preparation and Grading and Structural Fill subsections of this report. The
pavement subgrade should be proof -rolled with a heavy, rubber -tired piece of equipment, to identify
soft or yielding areas that require repair. The pavement section should be underlain by a stable
subgrade. We should be retained to observe the proof -rolling and recommend repairs prior to
placement of the asphalt or hard surfaces.
Utilities
We recommend that underground utilities be bedded with a minimum six inches of pea gravel prior to
backfilling the trench with on -site or imported material. Trenches within settlement sensitive areas
should be compacted to 95 percent of the modified proctor as described in the Structural Fill subsection
of this report. Trenches located in non-structural areas should be compacted to a minimum 90 percent
of the maximum dry density. The trench backfill compaction should be tested.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Brubaker Residence Settlement Evaluation
Edmonds, Washington
NGA File No. 1313321
December 10, 2021
Page 11
Site Drainage
Surface Drainage: In general, the ground around the residence should be regraded such that runoff is
directed away from the residence and collected in an appropriate stormwater collection system. Where
possible, 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 building. All surface water generated from paved areas and
roof drains should be collected by permanent catch basins and drain lines and be routed into an
approved discharge system. No surface water should be allowed to flow towards the slope. Existing
drains should be investigated and repaired, as needed, to ensure all runoff generated on this site is
routed away from the structure foundation and the slope.
Subsurface Drainage: If it is determined that foundation footing drains are not present around the
entire perimeter of the residence, we recommend that during the installation of the recommended
foundation improvements, an adequate foundation footing drain system be installed around the
structure. Footing drains should be installed at least six inches below bottom of the existing foundations.
The drains should consist of a minimum 4-inch-diameter, rigid, slotted or perforated, PVC pipe
surrounded by free -draining material wrapped in a filter fabric.
We recommend that the free -draining material consist of an 18-inch-wide zone of clean (less than three -
percent fines), granular material. Washed rock is an acceptable drain material. The free -draining
material should extend up 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
approved collection and discharge point with convenient cleanouts to prolong the useful life of the
drains. Roof drains should not be connected to wall or footing drains.
CONSTRUCTION MONITORING
We should be retained to provide construction monitoring services during the earthwork phase of the
project to evaluate subgrade conditions, temporary cut conditions, fill compaction, and drainage system
installation.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Brubaker Residence Settlement Evaluation
Edmonds, Washington
NGA File No. 1313321
December 10, 2021
Page 12
USE OF THIS REPORT
NGA has prepared this report for Terianne Brubaker and associated agents, for use in the planning and
design of the development 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 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 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.
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.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Brubaker Residence Settlement Evaluation
Edmonds, Washington
NGA File No. 1313321
December 10, 2021
Page 13
It has been a pleasure to provide service to you on this project. If you have any questions or require
further information, please call.
Sincerely,
NELSON GEOTECHNICAL ASSOCIATES, INC.
'Z'L'Z'z / fa�
Sarah L. Dunn
Staff Geologist
M21
Khaled M. Shawish, PE
Principal
SLD:KMS:ak
Six Figures Attached
NELSON GEOTECHNICAL ASSOCIATES, INC.
VICINITY MAP
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Not to Scale
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Project Number
IIELSOt1 GEOTECH111CAL
No.
Date
Revision
By
cK Z
Brubaker Residence
'
1
11/18/21
Original
DPN
Al
I
1313321
Settlement Evaluation
ASSOCIATES, II1C
Figure 1
Vicinity Map
Woodinville Office Wenatchee Office
17311-135th Ave. NE, A-500 105 Palouse St
Woodinville, WA 98072 Wenatchee, WA 98801
a
E
ww.nelsongeotech.com (425) 486-1669 / Fax. 481-2510 (509) 665-7696 / Fax: 665-7692
L
: � r
J
lei
( 4&
Existing
Residence
P_
LEGEND
Property line
B-1 r
0 20 40
Number and approximate
1 location of boring
r
Approximate Scale: 1 inch = 20 feet
A A' Approximate location
L� of cross-section u
e
Reference: Site Plan based on field measurements, observations, and aerial parcel map review.
c
Project Number Brubaker Residence , Il son GEOTECHIIICAL No. Date Revision By cK c
1313321 Settlement Evaluation ASSOCIATES, inn 1 11/18/21 Original DPN ABR
Schematic Site Plan ' Woodinville Office Wenatchee Office
Figure 2 17311-135th Ave. NE, A-500 05 Palouse St,
Woodinville, WA 98072 Wenatchee, WA 98801
w.nelsongeotechco,n (425)486-16691 Fax. 481-2510 (509) 665-7696 1 Fax: 665-7692 1
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x=�0 n 0 20 40 60 80 100 120 140
Distance (feet)
Exploration
v
m
N m Boring Designation � B_1
� 23
m 23 <-- SPT N-value
a
20
0
y Groundwater Level— 1 23 NOTES:
During Exploration 23 1) Stratigraphic conditions are interpolated between
23 the explorations. Actual conditions may vary.
o W Geologic Contact --j ? — —? 2) Elevations are approximate.
z (approximate)
D n
� X Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure.
\hi1l\comoanv\2021 NGA Proiect Folders\13133-21 Brubaker Settlement Edmonds\Draftina\CS.dwa
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
OF COARSE FRACTION
SILTY GRAVEL
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
ML
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, FAT CLAY
NO. 200 SIEVE
50 % OR MORE
ORGANIC
CH
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
IIELSOn GEOTECHnICAL
No.
Date
Revision
By
cK
313321
Brubaker Residence
B
Settlement Evaluation
ASSOCIATES, incI1
1
11/18/21
Original
DPN
ABR
Figure 4
Soil Classification Chart
Woodinville Office Wenatchee Office
311-135th Ave. NE, A-500 105 Palouse St.
Woodinville, WA 98072 Wenatchee, WA 98801
ww.nelsongeotech.com (425) 486-1669 / Fax: 481-2510 (509) 665-7696 / Fax: 665-7692
BORING LOG
B-1
Approximate Ground Surface Elevation: ??
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
10 20 30 40 50 50+
c
N
Piezometer
Installation -
Description
2
a 0,
CL o
3 3
c w
°' o
�'m
Ground Water
Data
Moisture Content
J
o f
O
a O
m U
@
�
(Percent ■)
o
(Depth in Feet)
c9
U)
a
10 20 30 40 50 50+
0m
J
Topsoil
Gray, fine to coarse sand with silt, gravel, and trace wood
debris (very loose, moist to wet) (FILL)
3
-becomes fine to coarse sand with silt and gravel, very
5
5
loose to loose, wet
4
6
-becomes orange -brown, silty fine to medium sand with
gravel and trace organics, loose, moist to wet
-becomes orange -brown to gray -brown, silty fine to
10
10
10
coarse sand with with trace charcoal, loose to medium
dense
-----------------
Gray to gray -brown, fine to coarse sand with gravel and
—
trace iron -oxide staining (very dense, moist to wet)
SW
75-10
' 15
15
— — — — — — — — — — — — — — —
Gray, fine to coarse sand with silt and gravel
— —
—
(very dense, wet)
20
20
SW-SM
57
'
-----------------
Gray, fine to medium sand with silt and gravel
—
(very dense, wet)
SP-SM
25
25
80
Boring terminated at 26.5 feet below existing grade on
11/08/2021. Groundwater seepage was not encountered
during drilling.
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 DS Direct Shear
to Piezometer PP Pocket Penetrometer Readings, tons/ft
Depth Driven and Amount Recovered ❑ Silica Sand
p �c 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
Brubaker Residence
IlELS011 GEOTECHIIICAL
No.
Date
Revision
By
cK
111821
Original
oPN
ABR
1313321
Settlement Evaluation
Boring Log
,
ASSOCIATES, inc
/f Woodinville Office Wenatchee Office
17311-135th Ave. NE, A-500 105 Palouse St.
Figure 5
Page 1 of 1
neiaongeotech.com (4,5) 86-'1669/Fa 948; 2510 (509 665-7696/Fax 9665-7692
BORING LOG
B-2
Approximate Ground Surface Elevation: ??
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
10 20 30 40 50 50+
c
N
Piezometer
Installation -
Description
2
a 0,
CL o
3 3
c w
°' o
�'m
Ground Water
Data
Moisture Content
J
o f
O
a O
m U
@
�
(Percent ■)
o
(Depth in Feet)
c9
U)
a
10 20 30 40 50 50+
0m
J
Gray to light brown, fine to medium sand with gravel, silt,
and trace organics (medium dense, moist to wet) FILL)
14
-becomes light brown to reddish brown, loose, with
5
5
iron -oxide staining
6
-becomes light brown
8
'
-----------------
Gray, fine to coarse sand with silt and gravel
—
10
10
(dense, moist)
46
SW-SM
-becomes very dense
84
' 15
15
-----------------
Gray, fine to medium sand with silt and gravel
—
(dense, moist)
20
20
SP-SM
45
'
-----------------
Gray, fine to coarse sand with silt and gravel
—
(very dense, moist to wet)
SW-SM
25
25
61
Boring terminated at 26.5 feet below existing grade on
11/08/2021. Groundwater seepage was not encountered
during drilling.
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 DS Direct Shear
to Piezometer PP Pocket Penetrometer Readings, tons/ft
Depth Driven and Amount Recovered ❑ Silica Sand
p �c 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
Brubaker Residence
IlELS011 GEOTECHIIICAL
No.
Date
Revision
By
cK
111821
Original
oPN
ABR
1313321
Settlement Evaluation
Boring Log
,
ASSOCIATES, inc
/f Woodinville Office Wenatchee Office
17311-135th Ave. NE, A-500 105 Palouse St.
Figure 6
Page 1 of 1
neisongeotech.com (4,5) 86-'1669/Fa 948; 2510 (509 665-7696/Fax 9665-7692