GEO REPORT - 999017 Larsen Property Short Plat and Residence Underpinning REVISED Report EdmondsNC7A
Main Office
17311— 135'h Ave NE, A-500
Woodinville, WA 98072
(425) 486-1669 - FAX (425) 481-2510
February 28, 2018
Carl and Sharon Larsen
9832 Marine View Drive
Mukilteo, Washington 98275
NELSON GEOTEECHNICAL
ASSOCIATES, INC.
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Preliminary Geotechnical Engineering Evaluation
Larsen Property Short Plat and Residence Underpinning
15729 — 75t' Place West
Edmonds, Washington
NGA File No. 999017
Dear Mr. and Mrs. Larsen:
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 —
Larsen Property Short Plat and Residence Underpinning — 15729 - 75t' 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
June 23, 2017.
The site is currently occupied by an existing single-family residence and detached garage within the lower
eastern portion of the property and an existing single-family residence with a daylight basement within
the central portion of the property. The ground surface within the site generally slopes gently to
moderately up to the east from 75th Place West along the western property line to the toe of a steep to very
steep west -facing slope within the central portion of the property. The steep to very -steep west -facing
slope ascends up to a relatively level to gently sloping bench area within the very eastern portion of the
property. We were informed that the existing residence within the central portion of the property has
experienced some foundation settlement throughout the years. We understand that the proposed
development plan consists of underpinning the central residence foundation to mitigate potential future
settlement of the structure. A detached garage is also proposed to be constructed along the eastern portion
of the central residence location between the toe of the steep slope and the residence. We also understand
that you wish to subdivide the existing property into three separate residential parcels. The existing
residences within the western and central portion of the property would be located on two of the parcels
and the upper bench area would be located on the third parcel. The upper eastern parcel will likely be
developed with a new single-family residence sometime in the future. Specific development plans and
stormwater handling plans were not available at the time this report was prepared.
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 overall
property is located in the designated "Zones B through D" generally located above 75t' Avenue West
extending east past the top of the steep to very steep west -facing slope. This report provides information
and discussion to fulfill the requirements of the City of Edmonds for construction within this area.
Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Summary - Page 2
We explored the site subsurface soil conditions with four drilled soil borings on August 7, 2017. Our
explorations indicated that the lower central portion of the site is underlain by undocumented fill and
historic landslide debris at shallow depths, with competent native Whidbey Formation deposits at depth.
The upper eastern portion of the site is underlain by competent native glacial soils at shallow depths with
competent native Whidbey Formation deposits at depth.
Based on our site reconnaissance and explorations, and our understanding of the proposed plans, we have
concluded that the proposed short plat subdivision, central residence underpinning, central property
garage construction and upper eastern lot development on this site should be feasible from a geotechnical
standpoint, provided that our recommendations are incorporated into the overall design and construction
of this project. 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.
Due to the relatively loose nature of the undocumented fill soil and landslide debris encountered in our
explorations within the lower portion of the site within the vicinity of the existing central residence, it is
our opinion that the undocumented fill and landslide debris soils have likely contributed to the settlement
and distress that has been observed within the central residence. Without foundation improvements, the
settlement and settlement -related distress are likely to continue. To limit future potential impacts to the
residence as a result of continued settlement, we recommend that all interior and exterior foundations,
along with all interior slabs -on -grade be supported on driven pin piles advancing through the
undocumented fill and landslide debris and terminating within the underlying native competent soils.
Due to tight access constraints within portions of the residence, some of these improvements may be
difficult to implement. We therefore should consult with the structural engineer and contractors on
adequate stabilization measures as plans are finalized. In the attached report, we have included
recommendations for pin pile foundation underpinning support.
We also recommend that any new foundations and slabs associated with the proposed garage within the
central property be supported on a deep foundation system consisting of driven pin piles. Due to the
proposed garage being located in close proximity to the toe of the steep slope within the upper eastern
portion of the property, we also recommend that the proposed garage be protected against potential slope
movement on the eastern uphill side by incorporating some type of a debris wall on that side. This is
further discussed in the attached report.
For the proposed development within the upper eastern parcel, we recommend that any proposed structure
foundations be designed to utilize conventional spread footings extending down to competent native soil
or structural fill extending to these soils. We recommend that any proposed structures be set back at least
60 feet from the top of the steep east -facing slope. In the attached report, we have included
recommendations for site grading, retaining walls, foundation support, and site drainage.
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
directed into the existing drainage system that is located along the southern portion of the property. No
water should be infiltrated or dispersed within the site or near the site slopes. Such activity may lead to
instability 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.
Preliminary Geotechnical Engineering Evaluation
Larsen Property Short Plat and Residence Underpinning
Edmonds, Washington
NGA File No. 999017
February 28, 2018
Summary - Page 3
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.
Khaled M. Shawish, PE
Principal
Table of Contents
INTRODUCTION.......................................................................................................................... I
SCOPE............................................................................................................................................2
SITE CONDITIONS......................................................................................................................2
SurfaceConditions....................................................................................................................
2
SubsurfaceConditions..............................................................................................................
3
HydrogeologicConditions........................................................................................................4
SENSITIVE AREA EVALUATION............................................................................................5
SeismicHazard......................................................................................................................... 5
ErosionHazard......................................................................................................................... 6
Landslide Hazard/Slope Stability............................................................................................. 6
CONCLUSIONS AND RECOMMENDATIONS.......................................................................7
General...................................................................................................................................... 7
Erosion Control and Slope Protection Measures....................................................................
10
Site Preparation and Grading..................................................................................................11
Temporary and Permanent Slopes..........................................................................................12
StructureSetbacks..................................................................................................................12
Foundation Improvements......................................................................................................
12
ShallowFoundations..............................................................................................................14
RetainingWalls......................................................................................................................15
StructuralFill..........................................................................................................................
16
Slab-on-Grade.........................................................................................................................17
PavementSubgrade................................................................................................................18
Site Drainage Improvements..................................................................................................18
USE OF THIS REPORT.............................................................................................................19
LIST OF FIGURES
Figure 1 — Vicinity Map
Figure 2 Site Plan
Figure 3 Cross -Section A -A'
Figure 4 Soil Classification Chart
Figures 5 through 8 Boring Logs
NELSON GEOTECHN/CAL ASSOCIA TES, INC.
Preliminary Geotechnical Engineering Evaluation
Larsen Property Short Plat and Residence Underpinning
15729 — 75' Place West
Edmonds, Washington
INTRODUCTION
This report presents the results of our preliminary geotechnical engineering evaluation for the proposed
Larsen Property Short Plat and Residence Underpinning project. The address for the site is 15729 - 75t'
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 and improvements. For our use in preparing this
report, we have been provided with an undated, untitled boundary and topographic showing the existing
site conditions.
The site is currently occupied by an existing single-family residence and detached garage within the lower
western portion of the property and an existing single-family residence with a daylight basement within
the central portion of the property. The ground surface within the site generally slopes gently to
moderately up to the east from 75th Place West along the western property line to the toe of a steep to very
steep west -facing slope within the central portion of the property. The steep to very -steep west -facing
slope ascends up to a relatively level to gently sloping bench area within the very eastern portion of the
property. We were informed that the existing residence within the central portion of the property has
experienced some foundation settlement throughout the years. We understand that the proposed
development plan consists of underpinning the central residence foundation to mitigate potential future
settlement of the structure. A detached garage is also proposed to be constructed along the eastern portion
of the central residence location between the toe of the steep slope and the residence. We also understand
that you wish to subdivide the existing property into three separate residential parcels. The existing
residences within the western and central portion of the property would be located on two of the parcels
and the upper bench area would be located on the third parcel. The upper eastern parcel will likely be
developed with a new single-family residence sometime in the future. Stormwater plans have not been
finalized at this time, but we anticipate that runoff generated on this site will be tighlined to discharge into
an existing stormwater system within the southern portion 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 complex area now
known as the North Edmonds Earth Subsidence & Landslide Hazard Area (ESHLA). The overall
property is located in the designated "Zones B through D" generally located above 75t' Avenue West
extending east past the top of the steep to very steep west -facing slope. Slide movement from the large-
scale slide complex and smaller localized slides within the complex can both affect this property. This
NELSON GEOTECHN/CAL ASSOCIATES, INC
Preliminary Geotechnical Engineering Evaluation
Larsen Property Short Plat and Residence Underpinning
Edmonds, Washington
NGA File No. 999017
February 28, 2018
Page 2
report provides information and discussion to fulfill the requirements of the City of Edmonds for
construction within this area.
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.
2. Explored the subsurface soil and groundwater conditions within the site with four
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 and
perform hand explorations within the steep slope area and interior portion of the central
residence, as needed.
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 the existing residence underpinning support.
9. Provide recommendations for retaining walls.
10. Provide recommendations for subgrade preparation.
11. Provide recommendations for site drainage and erosion control.
12. Document the results of our findings, conclusions, and recommendations in a written
geotechnical report.
SITE CONDITIONS
Surface Conditions
The western and central portions of the property are generally situated on gently to moderately sloping
ground above and to the east of 75t" Place West. The western portion of the property is occupied within
an existing residence and detached garage, while the central portion of the property is occupied with an
existing single-family residence with a daylight basement. The ground surface within the western and
central portions of the property slopes gently to moderately up to the east from 75t1i Place West to the toe
of the steep to very steep west -facing slope within the eastern portion of the property at gradients in the
range of approximately 2 to 18 degrees (3 to 32 percent). A series of concrete block retaining walls are
located within the sloping areas between the existing residences. The western and central portions of the
property are generally vegetated with grass and landscaping plants.
NELSON GEOTECHN/CAL ASSOC/A TES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Page 3
From the lower central portion of the site, the ground surface slopes steeply to very steeply up to the east
to a relatively level to gently sloping upper bench area at gradients in the range of 35 to 45 degrees (70 to
100 percent). The existing residence within the central portion of the site is located approximately 37 to
47 feet from the toe of the steep to very steep west -facing slope. The overall height of the steep slope is
approximately 100 feet. The existing site conditions, site topography, and interpreted subsurface
conditions are presented on Cross Sections A -A' in Figure 3. The steep slope and upper bench area are
generally vegetated with dense underbrush and young to mature trees. We did not observe any surface
water during our site visit on August 7, 2017. We also did not observe any groundwater emitting from
the site slopes, however we were informed that water seepage on the steep slope has been observed in the
past. We did not observe any indications of recent slope movement such as deep-seated landsliding,
however some minor erosion and sloughing was observed within portion of the upper most part of the
steep west -facing slope area.
The lower western and central portion of the property is accessed via an existing asphalt driveway located
along the southern portion of the property extending from 75t' Place West. The upper eastern portion of
the property is accessed via 72' Avenue West. The site is bordered to the north, south and east by
existing residential properties, and to the west by 75' Place West. 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 Geologicp of the
Edmonds East and Edmonds West Quadrangles, Snohomish and King Counties, Washington, by Mackey
Smith (U.S.G.S., 1975). The lower western and central portion of the site is mapped as old landslides
(Qols) while the upper eastern portion of the property is mapped as Esperance Sand deposits (Qe). 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 Esperance sand is described as thinly bedded
sand. We generally encountered undocumented fill and granular landslide debris underlain by fine-
grained silt and clay within the lower central portion of the property that we interpreted as native
Whidbey Formation soils. Our explorations within the upper eastern portion of the site generally
encountered native glacial till and Esperance sand soils with fine-grained sand, silt and clay soils that we
interpreted as native Whidbey Formations soils.
Explorations: The subsurface conditions within the site were explored on August 7, 2017 by drilling four
borings using a track -mounted limited -access drill rig to depths of approximately 46.5 to 51.5 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.
NELSON GEOTECHN/CAL ASSOC/A TES, INC
Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Page 4
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
through 8. 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.
Underlying the ground surface within Borings B-1 and B-2 within the lower central portion of the
property, we generally encountered very loose to medium dense, gray -brown to gray silty fine to medium
sand with varying amounts of gravel and organics that we interpreted as surficial undocumented fill and
historic granular landslide debris. Underlying the surficial undocumented fill and historic granular
landslide debris in B-2 at a depth of approximately 40 feet below the ground surface, we encountered very
stiff blue -gray silty with varying amounts of fine sand and clay that we interpreted as native Whidbey
Formation deposits. Boring B-1 was terminated within the historic granular landslide deposits at a depth
of 46.5 feet below the existing ground surface, while Boring B-2 was terminated within the native fine-
grained Whidbey Formation deposit at a depth of approximately 51.5 feet below the existing ground
surface.
Below the ground surface within Borings B-3 and B-4 within the upper eastern portion of the property
generally encountered approximately 20.0 to 25.0 feet of medium dense to dense, gray to orange -brown
silty fine to medium sand that we interpreted as native glacial soils. Underlying the native glacial soils in
Borings B-3 and B-4, we encountered medium dense/very stiff to very dense/very hard blue -gray to gray
silty fine sand and silt with varying amounts of sand that we interpreted as native Whidbey Formation
Deposits. Borings B-3 and B-4 were terminated within the native fine-grained Whidbey Formation
deposit at a depth of approximately 46.5 feet below the existing ground surface.
Hydrologic Conditions
Groundwater seepage was not encountered in our explorations. However, wet soil conditions were
encountered within the upper granular soils above the fine-grained siltier soils encountered at depth. It
is our opinion that any groundwater seepage encountered within the site would be 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 granular soils found within the landslide debris and the upper native glacial soils. The low
NELSON GEOTECHN/CAL ASSOC/A TES, INC
Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Page 5
permeability soil consists of underlying siltier soils. 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 at
depth within the western and central portions of the property, while medium dense/very stiff to very
dense/very hard native glacial soils and Whidbey Formation deposits were encountered within the upper
eastern portion of the property. Based on the 2015 International Building Code (IBC), the site conditions
best fit the description for Site Class E within the lower western and central portions of the property while
the site conditions best fit the description for Class D soils within the upper eastern portion of the
property. Tables 1 and 2 below provides seismic design parameters for the site that are in
conformance with the 2015 IBC, which specifies a design earthquake having a 2% probability of
occurrence in 50 years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps.
Table 1— 2015 IBC Seismic Design Parameters
(Lower Western and Central Portions of the Site)
Site Class
Spectral Acceleration
Spectral Acceleration
Site Coefficients
Design Spectral
at 0.2 sec. (g)
at 1.0 sec. (g)
Response
Ss
S 1
Parameters
Fa
F,
SDs
SDI
r—E
1.323
0.520
0.90
2.40
0.794
0.832
Table 2 — 2015 IBC Seismic Design Parameters
(Upper Eastern Portion of the Site)
Site Class
Spectral Acceleration
Spectral Acceleration
Site Coefficients
Design Spectral
at 0.2 sec. (g)
at 1.0 sec. (g)
Response
Ss
S 1
Parameters
Fa
F,
SDs
SD1
D
1.324
0.521
1.00
1.500
0.883
0.521
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.
NELSON GEOTECHNICAL ASSOCIA TES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Page 6
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 competent glacial and fine-grained soils interpreted to
underlie the site have a low potential for liquefaction or amplification of ground motion.
The glacial soils interpreted to form the core of the steep slopes within the site are considered stable with
respect to deep-seated slope failures. All steep slopes have the potential for shallow sloughing failures
during seismic events. Such events should not significantly affect the planned development provided the
foundations are designed with the recommended setback values, debris protection systems, and the slope
and drainage systems are maintained as described in this report.
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 vegetative cover and
the specific surface soil types, which are related to the underlying geologic soil units. The Soil Surveyof
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 Everett very gravelly sandy loam, 15 to 30 percent slopes within the lower
western portion of the site, Alderwood-Everett gravelly sandy loams, 25 to 70 percent slopes within the
central portion of the site and Alderwood-Urban land complex, 2 to 8 percent slopes within the upper
eastern portion of the site. These soils are described as having a slight to high erosion hazard. It is our
opinion that the site soils should have a slight to moderate hazard for erosion in areas that are not
disturbed and where 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 western and central portions of the site slope gently to moderately down to the west. A
steep west -facing slope is located above and to the east of the existing central residence within the eastern
portion of the property. Groundwater seepage was not observed on the sloping portions of the property
during site visit, however we understand that groundwater seepage has been observed on the steep slope
area in the past.
This site and the overall site vicinity lies within a known 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 foreseeable future is very low, extreme environmental conditions
NELSON GEOTECHN/CAL ASSOC/A TES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Page 7
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 "Zones B through D" 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 granular landslide debris to depths of about 40 feet below
the existing ground surface within the lower (central) portion of the property. Medium dense/stiff
undisturbed native soils were encountered below this material, which we interpret the core of the site
slopes 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 existing and proposed structures. 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, debris catchment,
erosion control, structure setbacks 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 and improvements, 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 by
other human activity in the general site vicinity. We consider this potential to be low.
NELSON GEOTECHN/CAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Page 8
In general, the site and steep slopes within the site currently appear 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 landslide debris and ground movement within the lower central
and western portions of the property. The potential for landslide and erosion hazards within this site will
greatly 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 fills and would provide recommendations for accomplishing the
desired grading while maintaining long-term stability.
In our opinion, based on our observations and our understanding of the prevailing building conditions, the
settlement and distress to the central residence is likely a result of long-term consolidation (settlement) of
the relatively loose undocumented fill and landslide debris soils that were encountered in our explorations
and is interpreted to underlie portions of the residence. It appears that this fill was likely placed during
the initial development of this property. Due to the varying nature of the overall density of the fill
encountered in our explorations, it is likely that some of the fill material was placed in a loose condition at
the time of residence construction, and throughout the years has been settling under the building loads. It
is likely that the foundations and slabs -on -grade will continue to experience steady settlement and
subsidence under the current conditions resulting in additional distress to the foundation, slabs and
utilities within the structure.
To mitigate this condition, we recommend that the all exterior and interior foundations along with all
slabs -on -grade affected by the ongoing settlement be supported on deep foundations consisting of driven
pin piles to transfer building loads through the undocumented fill and landslide debris down to the
underlying competent native soils. Lateral loads on the residence should be resisted by helical anchor
tiebacks. The exact location and extent of the pin piles and helical anchor tiebacks should be determined
by the structural engineer. We should be retained to discuss with the structural engineer the details of the
stabilization plans. We have provided recommendations for driven pin piles and helical anchor tiebacks
in the Foundation Improvements subsection of this report. We also recommend that after the pin pile
and helical anchor installation is completed, the remainder of the residence be closely monitored for any
signs of further distress, and additional stabilization measures be installed if signs of future distress are
observed.
We recommend that if a slab -on -grade is utilized in the lower portions of the proposed central 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
NELSON GEOTECHN/CAL ASSOCIATES, INC.
Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Page 9
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.
In addition to the foundation improvements, we recommend that the drainage picture surrounding the
existing central residence be improved. Such improvements should include confirming and/or
implementing the placement of footing drains around the building, and routing all downspouts and runoff
from all hard surfaces into a permanent discharge system. We recommend that these pipes be extended to
discharge to an approved system. This is further discussed in the Drainage Improvements subsection of
this report.
It is also our opinion that the proposed garage development along the eastern side of the existing central
residence is feasible from a geotechnical standpoint. We recommend that the foundations and slabs
associated with the proposed garage structure be supported on a deep foundation system consisting of
driven pin piles. We understand that the garage will be constructed along or very near the toe of the steep
west -facing slope. In our opinion, this should be feasible provided the foundation walls along the upslope
side of the garage be designed as recommended in this report. We recommend that the upslope portions
of the garage foundation be designed as debris walls and extend a minimum of four feet above finished
ground surface to protect the structure against potential failures on this slope. This is intended to provide
a catchment measure should any sloughing debris travel towards the garage during extreme weather or as
a result of an earthquake. Alternatively, a separate debris protection structure or fence could be utilized.
It is our opinion that the planned residence development within the upper eastern portion of the site is
feasible from a geotechnical standpoint. It is also our opinion that the soils that underlie the upper eastern
portion of the site and form the core of the steep west -facing slope should be stable with respect to deep-
seated earth movements, due to their inherent strength and slope geometry. However, shallow failures
could occur on the slopes in the loose surficial soil, especially during adverse weather or a significant
seismic event. Proper structure setbacks along with erosion and drainage control measures as
recommended in this report should reduce this potential. Our explorations indicated that the upper eastern
portion of the site is underlain by medium dense or better native glacial soils at relatively shallow depths.
The native glacial soils within the proposed upper eastern development area should provide adequate
support for foundation, slab, and pavement loads. We recommend that the structures within the upper
eastern portion of the site be designed utilizing shallow foundations. Footings should extend through any
loose surficial soil and be keyed into the underlying competent native soils. These soils should be
encountered roughly two to five feet below the existing ground surface within the planned development
area, with some potential localized areas of deeper loose soils in unexplored areas of the site. To protect
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Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
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Edmonds, Washington Page 10
the structures against potential failures on the slopes, we recommend that any proposed structures be set
back at least 60 feet from the top of the steep west -facing slopes. We should be retained to review final
structure locations and to observe foundation excavations prior to placing forms.
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 into an existing stromwater system along the southern
portion 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
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
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Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
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Edmonds, Washington Page 11
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. It may be possible for trees to 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.
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 upper eastern residence and garage footprints down to planned
elevations. 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 within the site. 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 work is to take place during periods of wet weather, extreme
care should be taken during site preparation as to 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.
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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 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:1 V). 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.
Structure Setbacks
Uncertainties related to building along steep slopes are typically addressed by the use of building
setbacks. The purpose of the setback is to establish a "buffer zone" between the structure and the top and
toe of the slope so that ample room is allowed for normal slope recession during a reasonable life span of
the structure. In a general sense, the greater the setback distance, the lower the risk of slope failures
impacting the structure. From a geological standpoint, the setback dimension is based on the slope's
physical characteristics, such as slope height, surface angle, material composition, and hydrology. Other
factors such as historical slope activity, rate of regression, and the type and desired life span of the
development are important considerations as well.
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We recommend that any proposed structures within the upper eastern portion of the property be set back
at least 60 feet from the top of the steep west -facing slope. We also understand that a proposed garage
structure may be constructed along the toe of the steep west -facing slope within the central portion of the
property. In our opinion, this is feasible provided that the uphill eastern side of the garage is designed as
a debris catchment wall and extends a minimum of four feet above the surrounding ground surface. We
should be retained to review final residence location and to observe foundation excavations prior to
placing forms. Any proposed development within the setback area, should be the subject of a specific
geotechnical evaluation. Under no circumstances should water be allowed to concentrate on the slopes,
during or after construction.
Foundation Improvements
Driven Pin Piles: We recommend that all interior and exterior foundation lines along with all impacted
slabs -on -grade associated with the central residence be supported on driven pin piles to transfer
foundation loads to the underlying native competent native materials found below the fill and landslide
debris. We also recommend that the foundations and slabs for the proposed garage associated with the
central residence also be supported on deep foundations consisting of driven pin piles. Due to the limited
access to the existing residence area, we anticipate that all interior areas to be underpinned will be
supported on 2-inch pin piles. However, the exterior foundations and foundations for the planned garage
could be supported by either 2-inch pin piles or 4-inch pin piles, if larger equipment can access these
areas. We recommend that the foundations and slabs associated with the proposed garage be supported
on 4-inch pin piles. We have provided recommendations for the two pin pile sizes, in this section. Our
explorations did not encounter any significant debris within the existing fill or landslide debris, however
there is a possibility that some obstructions within the fill may impede some of the piles. There should be
contingencies in the budget and design for additional/relocated piles to replace piles that may be
obstructed by debris. We also recommend that excavation equipment be available on site during pile
installation so that shallow obstructions can be removed from the planned pile locations.
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.
We recommend that the four -inch pipe piles, if utilized, be driven using a tractor -mounted hydraulic
hammer, with an energy rating of at least 1,100 foot -lb. For this pile and hammer size, we recommend a
design capacity of eight tons for each pile driven to refusal. The refusal criterion for this pile and hammer
size is defined as less than one -inch of movement during 15 seconds of continuous driving at a rate of 550
blows per minute or higher. We recommend using galvanized schedule 40 pipe for the 4-inch pin piles.
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Edmonds, Washington Page 14
Maintaining these recommendations for minimum hammer size and refusal criteria is essential for
obtaining a successful outcome.
Final pile depths should be expected to vary somewhat and will depend on the depth of the loose material
and landslide debris, the nature of the underlying competent soils. The pin piles should penetrate a
minimum of five feet into the competent native glacial soils below the fill material in order to develop the
design capacity. Based on our explorations within the vicinity of the central residence, we anticipate that
piles may need to be driven to a minimum depth of 50 feet below the ground surface to achieve the
minimum embedment depth into the competent native soils. Piles that do not meet this minimum
embedment criterion 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.
Due to the relatively small slenderness ratio of pin piles, maintaining pin pile confinement and lateral
support is essential in preventing pile buckling. The brackets and pin pile connections to the existing and
proposed foundation and slabs should be designed by the structural engineer.
Vertically driven pin piles do not provide meaningful lateral capacity. Due to the rigid pile support,
friction between the foundation and subgrade soil should not be considered for resisting lateral pressures
on this structure. We recommend that all lateral loads be resisted on the helical anchor tiebacks.
Shallow Foundations
For the upper eastern portion of the development, conventional shallow spread foundations should be
placed on undisturbed medium dense or better native soils. Medium dense to dense soils should be
encountered roughly two to five feet below the ground surface based on our explorations; however,
deeper areas of loose soil may be encountered in unexplored areas of the site. Where undocumented fill
or less dense soils are encountered at footing bearing elevation, the subgrade should be over -excavated to
expose suitable bearing soil.
Footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost
protection and bearing capacity considerations. Foundations should be designed in accordance with the
2015 IBC. Footing widths should be based on the anticipated loads and allowable soil bearing pressure.
Water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be
removed from the foundation excavation prior to placing concrete.
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For foundations constructed as outlined above, we recommend an allowable design bearing pressure of
not more than 2,000 pounds per square foot (psf) be used for the footing design for footings founded on
the medium dense or better native soils or structural fill extending to the native competent material. The
foundation bearing soil should be evaluated by a representative of NGA. We should be consulted if
higher bearing pressures are needed. Current IBC guidelines should be used when considering increased
allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation
settlement using the recommended allowable bearing pressure is estimated to be less than one inch total
and 1/2 inch differential between adjacent footings or across a distance of about 20 feet, based on our
experience with similar projects.
Lateral loads may be resisted by friction on the base of the footing and passive resistance against the
subsurface portions of the foundation. A coefficient of friction of 0.30 may be used to calculate the base
friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a
triangular equivalent fluid pressure distribution. An equivalent fluid density of 150 pounds per cubic foot
(pcf) should be used for passive resistance design for a level ground surface adjacent to the footing. This
level surface should extend a distance equal to at least three times the footing depth. These recommended
values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and
passive resistance, respectively. To achieve this value of passive resistance, the foundations should be
poured "neat" against the native medium dense soils or compacted fill should be used as backfill against
the front of the footing. We recommend that the upper one -foot of soil be neglected when calculating the
passive resistance.
Retaining Walls
Final grading and development plans were not available at the time this report was prepared but retaining
walls will likely be needed for the proposed development. We recommend that the uphill foundation wall
for the proposed garage within the central portion of the property be extended a minimum of four feet
above the finished ground surface to protect the structure against potential failures from the slope above.
This is intended to provide a catchment measure should any sloughing debris travel towards the garage
structure during extreme weather or as a result of an earthquake. Alternatively, a separate debris
protection structure or fence could be utilized. We also recommend that no window or door openings be
located on the uphill eastern side of the proposed garage within the central portion of the property.
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
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Edmonds, Washington Page 16
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 45 pcf
for yielding (active condition) walls, and 65 pcf for non -yielding (at -rest condition) walls. If the uphill
side of the proposed garage is intended to act as a debris wall, we recommend the above ground portion of
the garage wall be designed to resist an active pressure of 100 pcf.
These recommended lateral earth pressures are for a drained granular backfill and are based on the
assumption of a maximum 2H:1 V backfill inclinations and do not account for additional 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, or other surface loads. We are available
to provide consultation regarding additional loads on retaining walls during final design, if needed.
The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and
by passive resistance acting on the below -grade portion of the foundation. Recommendations for
frictional and passive resistance to lateral loads are presented in the Foundations subsection of this
report.
All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report.
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. The recommended level of compaction should still be maintained.
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 systems.
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
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Edmonds, Washington Page 17
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.
Slab -on -Grade
As mentioned earlier, we recommend that slabs -on -grade associated with the central portion of the
property be designed as a structural slab and fully supported on the deep foundation system consisting of
driven pin piles. Slabs associated with the upper eastern portion of the property should be supported on
subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. We
recommend that all floor slabs be underlain by at least six inches of free -draining gravel with less than
three percent by weight of the material passing Sieve #200 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 is optional, and is intended to be used to protect the vapor barrier
membrane and to aid in curing the concrete.
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Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Page 18
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.
Site Drainage Improvements
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. Existing drains within the property should be investigated and
repaired, as needed, to ensure all runoff generated on this site is routed away from the building foundation
and into the approved discharge system.
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 existing stormwater
system within the southern portion of the site.
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.
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Preliminary Geotechnical Engineering Evaluation NGA File No. 999017
Larsen Property Short Plat and Residence Underpinning February 28, 2018
Edmonds, Washington Page 19
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.
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 report for Mr. Carl Larsen 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
NELSON GEOTECHN/CAL ASSOCIATES, INC
Preliminary Geotechnical Engineering Evaluation
Larsen Property Short Plat and Residence Underpinning
Edmonds, Washington
NGA File No. 999017
February 28, 2018
Page 20
proper maintenance of drainage control measures at the site (the runoff from the impervious surfaces
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.
.st
NELSON GEOTECHNICAL ASSOC/A TES, INC.
Preliminary Geotechnical Engineering Evaluation
Larsen Property Short Plat and Residence Underpinning
Edmonds, Washington
NGA File No. 999017
February 28, 2018
Page 21
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.
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7
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Edmonds, WA
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164th St SC;
,V.All R N
Beach
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Meadowdale v n
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168th St SW 16
Meadowdale 30`
Middle School O
V
Project Number NELSON GEOTECHNICAL No. Date Revision By I CK10
999017 Larsen Property Short Plat N ASSOCIATES, INC. 1 8/10/17 Original DPN i_sB
Vicinity Map GEOTECHNICAL ENGINEERS &GEOLOGISTS z
Woodinville Office East Wenatchee Office r
Figure 1 7311-135th Ave. NE, A-500 5526 Industry Lane,#2 Cd
Woodinville, WA98072 East Wenatchee, WA 98802
(425) 486-1669 / Fax: 481-2510-nelsongeotech.com (509) 665-7696 / Fax: 665-7692
Z
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Approximate Location of Proposed Garage
Approximate Top of Slope 0
Existing Western Garage Approximate Toe of Slope y S
Approximate 60-foot N o
Existing Western Residence Steep Slope Setback ad r
F.I -, V a i � CS T-1
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d ❑d' e p 8• uA CB IT-1 L u?-I_o•r 2 -- Z _
LAG P ±26.811 248.14' Z r m
WENT IN CAS ? i ., `` T IE- 46,16 12" PV
T BENCHMARK F0 C P E L❑ N IE 45. (12" PV
CISC & PUNCH 9435 "
� _ +� 0.5' 8EL GRAD - _ 4 }20,400 FOUND 4" IR(7H PIPE W�7' IE 2 2'{6" PVC V
SITED 04/201 G.O7 EAST I£� 8-57' a" N TYPE - CB -2 .02 N x w
SSM G !E 28. [4" uNKw0W7+ _ _ 1 St29' 0
RIM=101.24� - - - - - OF PIPE
:TR CH=89.12H37:p43,�-.•.F+.@;ip GRCIUNO E=2 1.49 {12" HOPE PVC E W) CMT2 6.57' W
J N,E-Ol1T 5 1 243-29'[12" F LR
29"E 14,88' S — P ; ' 7.70 `.,. •,.';:C.`.•j' 142. ^� 243.2T[18" F V
HANDRAIL v ❑ 'l5� iu5 N SS SS — -gg7l IE=243.87'(12" C
TIN CASE
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AH W 'FLOW S IE=$7.57'(12" CMP W) FOUND REBAR & CAP S
TO NOR 8 IE-98-48'{t2" GAP E) 4YE! t691fi" - 2 25 in
0.69' N X 0.25' W RIM=99.7 SSMH "'� FI S C8 T-1
12" PVC FOUND BARE REBAR RIM-131.77' m iy S` No RIM=247.38•
12- PVC 0'06' N X 0,06' E C6 T-1 - C8 T-2 SEMH-� '� -� `� i llqRIfA=252-42' SSMH
RIM-128.48 CH=126.+7' RIM.14O-47' 2 AAA IE=245-tC'[12" CMP
1/2 CAP ' t FEAE IM=140.95' PORTION Or PIPE CTR CH=241.38 RIM=247.12'
] c7 0 T-1 t} IE=125.40'(18" PVC E) -OVT W1 I}==135.87'(12" CMp E] CTR H�134,10' 8" RTICAL PIPE ABOVE GROUND {IN E-OUT W) C7R CH=24}.87• IE=245.03'{12" CMP
+ �+ RIM-96.51' IE=125.20'(12" CMP W) IE=136.67'02" HOPE SE) (1N -OUT W) =145.51' [IN E,N.S-OUT W] CIO
1 a iE=91.89'[12- PVC S) IE-127.23'(4" PVC S) 135.62'[18" PVC W] IE-139-46'(12" 5) a
rf IE=92-39'(12" PVC NW) IE=139•66'(t2' E) - DRIP LINE TYP.
fE-92.71'(4" PVC E) a-t 13h �� r 1 VERTICAL PIPE IE=139.31'02" W)
O
L
Existing Central Residence �,
as
C�
o u)
a
LEGEND.
— — Property line
B-,
I _ Number and approximate
—� location of boring
A AApproximate location
of cross-section
Reference: Site Plan based on an undated, untitled plan provided by CIS Engineering.
0 50 100
Scale: 1 inch = 50 feet
a�
L
CC
J
w
E 1_
7 r
�
z o
U M)
0)
0 0)
L
a-
I / lmVA rluICUL ruIUCIb=VU- I / LdlbC[I rIU1./CILY JIIUIL rldL dIIU U
A A•
Southwest
East
250
B-3
B-4
250
45° 9_5„ Qvt/Qva
28
—r.�— 32—i-
za
31
30
45
32
43°
25
45
49
53
200
Approx. Main Floor Elevation: 142.1'
48 Qw
2
200
,W
Approx. Basement Floor Elevation: 133.4'
o
Existing /
Existing Block Walls
Central 35° /
aResidence
w
150
B_2 /
150
75th PI W
B-1 - —
E
----
0
12,
13 /
Q
(landslide debris)
7 3
z 24
100--Qols
„ 17
100
zo /• 2s
0 / / 0
.
Qw
50
0 50 100 150 200 250 300 350 400 450 500 550 600
Distance (feet)
Exploration
Boring Designation --> B_1
23
23 <-- SPT N-value
Groundwater Level --> 1 z3
During Exploration 23
23
Geologic Contact
(approximate)
Reference: Cross Section is based on field measurements using a hand-held clinometer and 100-ft tape measure.
NOTES:
1) Stratigraphic conditions are interpolated between
the explorations. Actual conditions may vary.
2) Elevations are approximate.
50
Cur
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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
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
999017
Larsen Property Short Plat
Soil Classification Chart
NGA ASSOCIATES, INC.
GEOTECHNICAL ENGINEERS & GEOLOGISTS
1
8/10/17
Original
DPN
LSB
Figure 4
Woodinville Office East Wenatchee Office
11311-135lh Ave. NE, A-500 5526 Industry Lane, #2
Weedlnville, WA 98072 East Wenatchee, WA 98802
(425) 486-1669 / Fax:481-2510-nelsongeotech.corn (509) 665-7696 / Fax: 665-7692
BORING LOG
B-1
Approximate Ground Surface Elevation: ??
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
N
Piezometer
10 20 30 40 50 50+
Installation -
`E
Ground Water
Description
0. o>
a o
> -0
3
Q •°
Moisture Content
o
m
Data
Co J
o f
O
m 0
U
E m L
(Percent - 0)
O
(Depth in Feet)
C�
cn
U) J a
10 20 30 40 50 50+
a
J
Gray -brown, silty fine to medium sand with gravel,
—
iron -oxide staining, and trace roots (very loose, moist)
—
3
-becomes dark brown
—
—
3
5
5
-becomes dark brown to gray -brown, loose
5
-no organics
=
-becomes gray, moist to wet
—
—
7
10
10
-becomes gray -brown
—
9
SM
15
15
—
9
�
-becomes gray, medium dense, wet
—
—
17
20
20
-becomes loose with trace organics, charcoal
—
—
5
25
25
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
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
999017
Larsen Property Short Plat
N ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Woodinville Office East Wenatchee Office
17311-135th Ave. NE, A-500 5526 Industry Lane, #2
8072 East Wenatchee, WA 98802
1
8110/17
Original
DPN
LSB
Figure 5
Page 1 of 2
(425)) 486 11669 / Fax 9481 2510 www nelsongeotech corn (509) 6 5-7696 1 Fax' 665--7692
BORING LOG
B-1 (cont.)
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
10 20 30 40 50 50+
N
Piezometer
Installation -
2
1
Ground Water
Description
a o>
a o
3
Q •°
Moisture Content
o
Data
o T
O
m a
U
m L
(Percent - �)
o
(Depth in Feet)
C�
co
U) J
10 20 30 40 50 50+
a
J
Orange -brown to gray -brown, silty fine to medium sand
—
2
with gravel, trace organics, and charcoal (very loose, wet)
—
-becomes gray to brown, with trace iron -oxide staining,
—
35
35
medium dense
—
17
'
-no organics or charcoal
—
SM
-becomes gray, with trace gravel
_—
40
40
-no iron -oxide staining
20
'
—
45
45
-with trace iron -oxide staining
—
19
Boring terminated below existing grade at 46.5 feet on
8/7/17. Groundwater seepage was not encountered
during drilling.
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 sm 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
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
999017
Larsen Property Short Plat
N ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Woodinville Office East Wenatchee Office
17311-135th Ave. NE, A-500 5526 Industry Lane, #2
8072 East Wenatchee, WA 98802
1
8110/17
Original
DPN
LSB
Figure 5
Page 2 of 2
(425)) 486 11669 / Fax 9481 2510 www nelsongeotech corn (509) 6 5-7696 1 Fax' 665--7692
BORING LOG
B-2
Approximate Ground Surface Elevation: ??
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
N
Piezometer
10 20 30 40 50 50+
Installation -
`E
Ground Water
Description
0. o>
a o
> -0
3
Q •°
Moisture Content
o
m
Data
Co J
o f
O
m 0
U
E m L
(Percent - 0)
O
(Depth in Feet)
C�
cn
U) J a
10 20 30 40 50 50+
a
J
Gray -brown, silty fine to medium sand with gravel and
—
roots (very loose to loose, moist)
—
4
5
5
-becomes gray with iron -oxide staining, loose
—
5
-no roots
-becomes gray to orange -brown
=
6
'
-becomes gray with trace gravel and roots
—
7
10
10
-becomes gray -brown
—
8
-becomes medium dense
—
SM
15
15
-no roots
—
11
-becomes wet, with gravel
—
—
13
20
20
-becomes gray, with trace gravel
—
—
13
' 25
25
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
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
999017
Larsen Property Short Plat
N ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Woodinville Office East Wenatchee Office
17311-135th Ave. NE, A-500 5526 Industry Lane, #2
8072 East Wenatchee, WA 98802
1
8110/17
Original
DPN
LSB
Figure 6
Page 1 of 2
(425)) 486 11669 / Fax 9481 2510 www nelsongeotech corn (509) 6 5-7696 1 Fax' 665--7692
BORING LOG
B-2 (cont.)
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
10 20 30 40 50 50+
N
Piezometer
Installation -
2
1
Ground Water
Description
a o>
a o
3
Q •°
Moisture Content
o
Data
o T
O
m a
U
m L
(Percent - �)
o
(Depth in Feet)
C�
co
U) J
10 20 30 40 50 50+
a
J
Gray, silty fine to medium sand with gravel, iron -oxide
—
8
staining, and trace charcoal (loose, wet)
-becomes medium dense
-no charcoal
—
SM
24
35
35
17
' 40
40
Gray -blue silt with fine sand (very stiff, dry)
ML
29
' 45
45
50
50
30
Boring terminated below existing grade at 51.5 feet on
8/7/17. Groundwater seepage was not encountered
during drilling.
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 sm 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
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
999017
Larsen Property Short Plat
N ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Woodinville Office East Wenatchee Office
17311-135th Ave. NE, A-500 5526 Industry Lane, #2
8072 East Wenatchee, WA 98802
1
8110/17
Original
DPN
LSB
Figure 6
Page 2 of 2
(425)) 486 11669 / Fax 9481 2510 www nelsongeotech corn (509) 6 5-7696 1 Fax' 665--7692
BORING LOG
B-3
Approximate Ground Surface Elevation: ??
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
N
Piezometer
10 20 30 40 50 50+
Installation -
`E
Ground Water
Description
0. o>
a o
> �
3
Q •°
Moisture Content
o
m
Data
Co J
o f
O
m 0
U
E m L
(Percent - 0)
O
(Depth in Feet)
C�
cn
U) J a
10 20 30 40 50 50+
a
J
Gray -brown to orange -brown, silty fine to medium sand
with gravel, iron -oxide weathering, and trace metal/plastic
(dense, moist) (FILL)
41
Gray to orange -brown, silty fine to medium sand with
—
5
5
gravel, iron -oxide weathering, and trace roots (very
_
54
dense, moist)
-becomes orange -brown to gray
-no roots
—
—
50-6"
-becomes gray, medium dense
—
—
23
10
10
SM
-no iron -oxide staining
—
—
29
' 15
15
-becomes gray -brown with iron -oxide staining,
_
32
20
20
dense, wet
— — — — — — — — — — — — — — —
Gray silt with fine sand (very stiff, moist)
— —
—
31
' 25
25
ML
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
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
999017
Larsen Property Short Plat
N ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Woodinville Office East Wenatchee Office
17311-135th Ave. NE, A-500 5526 Industry Lane, #2
8072 East Wenatchee, WA 98802
1
8110/17
Original
DPN
LSB
Figure 7
Page 1 of 2
(425)) 486 11669 / Fax 9481 2510 www nelsongeotech corn (509) 6 5-7696 1 Fax' 665--7692
BORING LOG
B-3 (cont.)
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
10 20 30 40 50 50+
N
Piezometer
Installation -
2
1
Ground Water
Description
a o>
a o
3
Q •°
Moisture Content
o
Data
o T
O
m a
U
m L
(Percent - �)
o
(Depth in Feet)
C�
co
U) J
10 20 30 40 50 50+
a
J
Gray -brown, silty fine to medium sand with iron -oxide
—
30
staining (medium dense to dense, moist)
—
—
SM
—
—
25
35
35
Gray silt with fine sand (very stiff, moist)
ML
Gray, silty fine sand with iron -oxide staining —
(dense, moist) -
-
45
40
40
—
SM
—
45
45
—
48
Boring terminated below existing grade at 46.5 feet on
8/7/17. Groundwater seepage was not encountered
during drilling.
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 sm 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
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
999017
Larsen Property Short Plat
N ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Woodinville Office East Wenatchee Office
17311-135th Ave. NE, A-500 5526 Industry Lane, #2
8072 East Wenatchee, WA 98802
1
8110/17
Original
DPN
LSB
Figure 7
Page 2 of 2
(425)) 486 11669 / Fax 9481 2510 www nelsongeotech corn (509) 6 5-7696 1 Fax' 665--7692
BORING LOG
B-4
Approximate Ground Surface Elevation: ??
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
N
Piezometer
10 20 30 40 50 50+
Installation -
`E
Ground Water
Description
0. o>
a o
> �
3
Q •°
Moisture Content
o
m
Data
Co J
o f
O
m 0
U
E m L
(Percent - 0)
O
(Depth in Feet)
C�
cn
U) J a
10 20 30 40 50 50+
a
J
Gray -brown, silty fine to medium sand with gravel,
—
iron -oxide staining, and trace organics (loose, moist)
—
SM
_
7
— — — — — — — — — — — — — — —
— —
—
5
5
No recovery
2
— — — — — — — — — — — — — — —
Gray, silty fine to medium sand with gravel and iron -oxide
— —
—
weathering (dense, moist)
—
—
41
-becomes medium dense
—
—
25
' 10
10
SM
-becomes gray -brown
—
—
28
' 15
15
—
35
' 20
20
Gray silt with fine sand (hard, moist)
-interbedded with gray, silty fine to medium sand with
25
25
gravel
ML
45
'
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
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
999017
Larsen Property Short Plat
N ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Woodinville Office East Wenatchee Office
17311-135th Ave. NE, A-500 5526 Industry Lane, #2
8072 East Wenatchee, WA 98802
1
8110/17
Original
DPN
LSB
Figure 8
Page 1 of 2
(425)) 486 11669 / Fax 9481 2510 www nelsongeotech corn (509) 6 5-7696 1 Fax' 665--7692
BORING LOG
B-4 (cont.)
Soil Profile
Sample Data
Penetration Resistance
(Blows/foot - 0)
10 20 30 40 50 50+
N
Piezometer
Installation -
2
1
Ground Water
Description
a o>
a o
3
Q •°
Moisture Content
o
Data
o T
O
m a
U
m L
(Percent - �)
o
(Depth in Feet)
C�
co
U) J
10 20 30 40 50 50+
a
J
Gray silt with fine sand (very stiff to hard, moist)
32
49
' 35
35
-interbedded with gray, silty fine to medium sand
ML
40
40
53
'
45
45
52
Boring terminated below existing grade at 46.5 feet on
8/7/17. Groundwater seepage was not encountered
during drilling.
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 sm 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
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
999017
Larsen Property Short Plat
NGA ASSOCIATES, INC.
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Woodinville Office East Wenatchee Office
17311-135th Ave. NE, A-500 5526 Industry Lane, #2
8072 East Wenatchee, WA 98802
1
8110/17
Original
DPN
LSB
Figure 8
Page 2 of 2
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