Aug 23 2012 geotech report BLD20120858.pdfREVISED GEOTECHNICAL
ENGINEERING REPORT
OLSON RESIDENCE
15500 - 75TH PLACE WEST
EDMONDS, WASHINGTON
PREPARED FOR
MR. GEORGE OLSON
NELSON• '
ASSOCIATES9 INC.
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Main Office
17311 —135" Avenue NE, A-500
Woodinville, WA 98072
(425) 486-1669 FAX (425) 481-2510
(425) 337-1669 Snohomish County
July 15, 2011
Mr. George Olson
3528 -102°a Place SE
Everett, WA 98208
- Revised Geotechnical Engineering Report
Olson Residence
15500 - 75`h Place West
Edmonds, Washington
NGA File No. 8342B11
Dear Mr. Olson:
Engineering -Geology Branch
437 East Penny Road
Wenatchee, WA 98801
(509) 665-7696 FAX (509) 665-7692
We are pleased to submit the attached report titled "Revised Geotechnical Engineering Report - Olson
Residence - 15500-75t' 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 based on updated plans. Our services were
completed in general accordance with the proposal signed by you on March 23, 2011.
We previously conducted a preliminary assessment of the property in October 2010 and provided you
with verbal opinions regarding the site and potential development, as part of your feasibility evaluation.
At that time, we explored the site with two geotechnical borings. Our explorations indicated that the site
is generally underlain by silty fine to medium sand near the surface, and silt with sand at depth. We
interpreted that the majority of the deposits underlying the sit consist of landslide debris with Whidbey
Formation silts at depth. We provided you a preliminary report dated April 27, 2011 based on previous
development plans. The current plans have been revised to reduce impacts to the site. This revised report
addresses the most recent plans.
The site is situated on gently to steeply sloping ground that descends to the right-of-way for the
Burlington Northern Santa Fe railroad and the shore of Puget Sound. Current project plans consist of
constructing a two-story single-family residence with a daylight basement on the eastern portion of the
property. Retaining walls up to nine feet in height are planned. The lower floor slab will be designed as a
structural slab and will be entirely supported on auger cast piles. A small soldier pile retaining wall is
planned near the northeastern corner of the site to replace a failed ecology block retaining wall.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75t' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Summary - Page 2
Stormwater handling plans have not been finalized at this time, but we understand that they will include
tightlining the runoff down to the bottom of the slope.
The site is mapped as part of the large historic/prehistoric Meadowdale Landslide complex and is located
in the designated "Zone A" within the lower portion of the slide complex. This report provides
information and discussion to fulfill the requirements of the City of Edmonds for construction within this
area of Edmonds. It is important to recognize that the site and overall vicinity is part of this ancient
landslide, and that development plans and future activity on this property should take that into
consideration.
It is our opinion that the site is generally compatible with the planned development of a single family
residence. It is also our opinion that the slope on the eastern side of 75t1i Place West, also know as Lunds
Gulch Road, is relatively stable. Based on the slide debris encountered in our explorations, and close
proximity of the planned residence to the steep slopes, we recommend supporting the planned residence
on a deep foundation system (drilled piers) extending to the more competent cohesive soils encountered at
depth. The piers are intended to provide support for the residence and also provide an effective setback
from the steep slopes. Specific recommendations for foundation design and installation are provided in
the attached report.
A steep slope is located on the uphill side of the property on the other side of 75�' Place West. This slope
appears to be relatively stable and does not appear to pose serious risks to the planned improvements.
Some debris/mudflow events may occur on this slope from time to time, especially during significant
rainfall; however, with the presence of the road below this slope and the distance planned between the
residence and the edge of the road, we are of the opinion that debris protection systems are not needed at
this time.
During our most recent site reconnaissance on March 30, 2011, we observed that a shallow landslide had
occurred on the steep portion of the site slopes above the railroad tracks. The slide was located along the
southern property line, and seems to have been triggered by water flow off of 75 h Place West which made
its way towards the steep slope. This water flow appears to have been occurring fairly frequently as
evident by the channeling of sediment deposition along the southern property line starting at the road
edge. This water flow should be collected and handled within any future drainage system planned as part
of this development. Also, the recent landslide should be stabilized to reduce potential adverse impacts
on the remainder of the site, and/or the railroad tracks below. We have provided general
recommendations for stabilizing the landslide in the attached report.
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, be collected in a tightline and
routed to the bottom of the slope. If this alternative is not feasible, the collected water should be pumped
into the existing system in the roadway. No water should be infiltrated or dispersed on or near the site
slopes. Such activity may cause further sliding within the steep 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.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75 h Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Summary - Page 2
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
Two Copies Submitted
cc: James Thomas — Architectural Design Associates
John McDonnell — JC McDonnell Engineering PC (via e-mail)
INTRODUCTION....................................................................................................................................... I
SCOPE.........................................................................................................................................................2
SITECONDITIONS...................................................................................................................................2
SurfaceConditions.....................................................................................................................................2
SubsurfaceConditions...............................................................................................................................3
HydrologicConditions...............................................................................................................................4
SENSITIVEAREA EVALUATION.........................................................................................................5
SeismicHazard..........................................................................................................................................5
ErosionHazard..........................................................................................................................................5
LandslideHazard/Slope Stability..............................................................................................................6
CONCLUSIONS AND RECOMMENDATIONS....................................................................................7
General.......................................................................................................................................................
7
Erosion Control and Slope Protection Measures.....................................................................................10
StructureSetbacks...................................................................................................................................10
SitePreparation and Grading...................................................................................................................11
Temporaryand Permanent Slopes..........................................................................................................
FoundationSupport .................................................................................................................................13
StructuralFill...........................................................................................................................................13
RetainingWalls.......................................................................................................................................14
StructuralSlab.........................................................................................................................................15
SoldierPile Wall......................................................................................................................................16
PavementSubgrade.................................................................................................................................17
Repairsof Recent Landslide....................................................................................................................
is
- Site Drainage...........................................................................................................................................18
USEOF THIS REPORT..........................................................................................................................20
LIST OF FIGURES
Figure 1 — Vicinity Map
Figure 2 — Site Plan
Figure 3 — Cross Sections A -A'
Figure 4 — Soil Classification Chart
Figures 5 and 6 — Boring Logs
Figure 7 — Hand Auger Logs
NELSON GEOTCHNICAL ASSOCIATES, INC.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75th Place West
Edmonds, Washington
_ INTRODUCTION
This report presents the results of our geotechnical engineering evaluation of the most recent plans for the
_ Olson Residence project. The site is located at 15500 — 75`'' Place West in Edmonds, Washington, as
shown on the Vicinity Map in Figure 1. We previously prepared a report dated April 27, 2011 for a prior
site layout. The purpose of the study is to explore and characterize the surface and subsurface conditions
at the site and provide general geotechnical recommendations for site development. For our use in
preparing this revised report, we were provided with an undated site plan titled "Foundation Plan,"
prepared by Architectural Design Associates, PS, dated July 11, 2011. Along with other foundation
notes, this plan shows the building layout and pile support configurations. We were also provided with an
undated Plan Sheet SP1.0 titled "Site Plan." The plan shows the site topography, property lines, and the
planned residence footprint.
The site is situated on sloping ground that descends to the right-of-way of the Burlington Northern Santa
Fe (BNSF) railroad and the shore of Puget Sound. Project plans consist of constructing a two-story,
single-family, daylight basement residence on the eastern portion of the property. Retaining walls up to
nine feet in height are planned. Auger cast piles will be used to support the entire structure, as well as an
elevated driveway for garage access which will be entered on the upper floor elevation of the residence.
The lower floor slab will be designed as a structural slab and will be entirely supported on auger cast
piles. A small soldier pile retaining wall is planned near the northeastern corner of the site to replace a
failed ecology block retaining wall. Stormwater plans have not been finalized at this time, but we
understand they may include tightlining runoff down to the bottom of the slope. The current site layout is
shown on the Site Plan in Figure 2.
The site is mapped as part of the large historic/prehistoric Meadowdale Landslide area. Slide movement
from the large-scale slide complex and small slides within the complex can both affect this property. The
residence design has taken this into consideration.
YELSON GEOTECHNICAL ASSOCIATES, INC.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75"' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Page 2
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. Explore the subsurface soil and groundwater conditions within the site with two
approximately 25-foot deep geotechnical borings using a portable drill rig. The drill rig
was subcontracted by NGA.
3. Meet with you and your representatives and discuss our findings and options for site
development.
4. Conduct explorations on the site slopes using hand tools.
5. Map the conditions on the slope and evaluate current slope stability conditions.
6. Perform laboratory classification and analysis of soil samples, as necessary.
7. Provide recommendations for earthwork, foundation support, and slabs -on -grade in
accordance with the City of Edmonds standards for development in the North Edmonds
ESLHA.
8. Provide recommendations for subgrade preparation.
9. Provide recommendations for retaining walls and shoring.
10. Provide recommendations for debris walls/fences, as needed.
- 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 site is situated on a gentle to steep west -facing slope overlooking Puget Sound. The central portion
of the property consists of a gently sloping bench. To the east of the gently sloping bench, a steep but
short, slope extends up to 75th Place West. Below the gently sloping bench, the ground surface slopes
steeply down to the existing railroad tracks and Puget Sound. There is a very steep slope above 75"' Place
West directly above this lot, with silt exposures and signs of soil creep and erosion. A cut along the road
has experienced sloughing, but the steep slope above the road appears to be relatively stable. The site is
vegetated with brush and deciduous trees. We observed evidence of surface water flow from the road
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75 h Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B11
Page 3
onto the property near the southern property line during our most recent visit on March 30, 2011. An
approximate 6-foot tall block retaining wall that is failing is located just to the east of the eastern property
line, directly below the road. It appears that this wall was constructed to support the 75"' Place West.
A steep west -facing slope is located along the western portion of the property. This steep slope descends
to the BNSF railroad tracks at about 28 to 35 degrees (53 to 70 percent). The slope inclinations are
shown on Cross -Section A -A' in Figure 3
Subsurface Conditions
Geology: The geologic units for this area are shown on the Geologic Map of the Edmonds East and Part
of the Edmonds West Quadrangles, Washington, by James P. Minard (USGS, 1983). The site is mapped
-- as Olympia Gravel — Qog, and Whidbey Formation — Qw. The Olympia Gravel deposit generally
consists of stratified, fluvial sand and gravel. The Whidbey Formation generally consists of compact,
medium to coarse grained sands. Our explorations encountered silty sand and silt material, considered
mostly as slide debris.
Explorations: The subsurface conditions within the site were explored on October 28, 2010 by drilling
two borings using a limited -access drill rig to depths of approximately 21.5 to 26.5 feet below the existing
ground surface. We also explored the steep slopes on March 30, 2011 with hand augers to depths of
approximately 3.5 to 4.0 feet. 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
and hand augers.
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.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75"' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B11
Page 4
_ The soils were visually classified in general accordance with the Unified Soil Classification System,
presented in Figure 4. The logs of our borings are attached to this report and are presented as Figures 5
and 6. The logs of our hand augers are attached and are presented as Figure 7. We present a brief
summary of the subsurface conditions in the following paragraphs. For a detailed description of the
subsurface conditions, the boring and hand auger logs should be reviewed.
Borings: At the surface of the explorations, we encountered approximately eight to ten feet of loose to
medium dense, gray -brown to gray, fine to medium sand with silt to silty fine to medium sand. This
material was underlain by approximately two to five feet of stiff to very stiff, gray silt mottled with iron -
oxide staining, and contained possible slickensides which could indicate previous soil movement. The
gray silt was underlain by blue -gray and some tan, very stiff to hard, silt to sandy silt. We interpreted the
-- soil encountered in the borings to be mostly landslide debris with the Whidbey Formation silts at the
bottom of the slide debris. Borings 1 and 2 were terminated at depths of 26.5 feet and 21.5 feet below the
existing ground surface, respectively.
Hand Augers: Below a surficial topsoil layer, we encountered approximately two feet of soft, brown -gray
sandy silt with organics. We interpreted this soil as possible older landslide debris. Below this material,
_ we encountered soft to very stiff, blue -gray to gray, sandy silt. We interpreted this soil to be part of the
upper portion of the Whidbey Formation. Hand Augers 1, 2, and 3 were terminated in the sandy silt
material at depths of 3.5 feet to 4.0 feet below the existing ground surface, respectively.
Hydrologic Conditions
Groundwater seepage was not encountered in the explorations, although it is our opinion that deep
groundwater regimes likely exist below the site. If shallow ground water is encountered on this site, we
would expect it to be a perched groundwater condition. Perched water occurs when surface water
infiltrates through less dense, more permeable soils and accumulates on top of underlying, less permeable
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 precipitation. We would
expect the amount of perched water to decrease during drier times of the year and increase during wetter
periods.
Revised Geotechnical Engineering Report
Olson Residence
- 15500 - 75t' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B11
Page 5
Evidence of surface water was observed from 75 h Place West onto the property near the southern
property line. This water appears to flow on the ground surface along that side of the property and then
disappears into the ground. This water flow was likely the cause of the most recent landslide above the
railroad tracks.
SENSITIVE AREA EVALUATION
Seismic Hazard
Undocumented fill and medium stiff to hard cohesive soils were encountered underlying the site. Based
on the 2009 International Building Code (IBC), the site conditions best fit the description for Site Class
Q
— Hazards associated with seismic activity include liquefaction potential and amplification of ground
motion by soft or loose geologic deposits. Liquefaction is caused by a rise in pore pressures in a loose,
fine sand deposit beneath the groundwater table. It is our opinion that the medium dense/stiff or better
native soils interpreted to underlie the site have a low potential for liquefaction or amplification of ground
— motion; however these materials could experience instability as a result of seismic activity. Shallow
sloughing failures may occur in the loose surficial soils on the slopes during seismic events.
Erosion Hazard
The criteria used for determining the erosion hazard for the site soils includes soil type, slope gradient,
vegetation cover, and groundwater conditions. The erosion sensitivity is related to the vegetative cover
_ and the specific surface soil types, which are related to the underlying geologic soil units. The Soil
Survey of Snohomish County Area, Washington, by the Soil Conservation Service (SCS) was reviewed to
determine the erosion hazard of the on -site soils. The site surface soils were classified using the SCS
classification system as Alderwood-Everett gravelly sandy loams, 25 to 70 percent slopes. These soils are
listed as having a moderate hazard of water erosion, and on the steeper portions of the slope the erosion
hazard is considered high. These soils should have a low to moderate hazard for erosion in areas that are
not disturbed and where the vegetation cover is not removed.
• • •
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75"' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Page 6
Landslide Hazard/Slope Stability
The criteria used for the evaluation of landslide hazards include soil type, slope gradient, and groundwater
conditions. The site slopes moderately to steeply down to the west. Groundwater seepage was not
observed on the slopes; however, evidence of water flow was observed along the southern property line
from 75"' Place West.
This site and the overall site vicinity lies within an ancient landslide area. The site and vicinity have been
relatively stable for a very long period of time, and development in the area has taken place in the form of
single-family residences and roadways. Although the likelihood of the ancient slide to become active in
- the forseable future is very low, extreme environmental conditions coupled with inadequate human
practices could re -activate the ancient landslide. Such external factors could include severe and elongated
--- weather events and/or significant seismic activity.
The site falls within "Zone A" of the North Edmonds Earth Subsidence and Landslide Hazard Area
Report prepared by Landau Associates for the City of Edmonds. This designation requires that certain
features be included (or excluded) in the design. Such features include the restriction of cuts and fills, the
need for tightlining runoff into an approved system, the need to design foundations and retaining walls to
withstand high lateral earth pressures and potential loss of soil beneath parts of the foundation, and 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 the requirements in the remainder of this report.
We encountered evidence of a potential slope movement as evident by the slickensides in the silt at
depths of about 15 to 20 feet below the existing ground surface. Hard, competent silt was encountered
below this material and we interpret the core of the slope to consist primarily of relatively stable material.
We should note, however, that potential deep-seated slide planes were reported to be up to 100 feet deep
below this site.
We observed a recent landslide on the southwestern portion of the property during our most recent visit.
_ A small wall is located at the toe of the slope along the BNSF Railroad right-of-way. It appears that the
slide debris partially filled up the area behind the wall. In general, localized areas of surface instability
and surface sliding can occur on steep slopes. Backwasting (movement of near -surface soil) through soil
�` •
Revised Geotechnical Engineering Report
Olson Residence
15500 - 75 h Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B11
Page 7
erosion processes and local surface slides is common to steep slopes, particularly where the soils are
exposed to weathering. Normal surface erosion and shallow sloughing failures should be expected to
occur on the steep slope to the west from time to time.
The Puget Sound area has experienced significant rainfall throughout the fall, winter, and early spring. It
appears that this recent landslide is related to the rainfall and the water runoff onto the property from 75`s
Place West. We recommend that the landslide be repaired, and that the water runoff be diverted to an
appropriate system and not be allowed to flow uncontrollably onto the property. We discuss these topics
further in the Repairs of Recent Landslide and Drainage subsections of this report, respectively. In this
report, we have also provided geotechnical recommendations for deep -foundation support, erosion
control, and other development considerations that should reduce the potential impact of site development
on the site slopes and the steep slope to the west.
CONCLUSIONS AND RECOMMENDATIONS
General
It is our opinion, from a geotechnical standpoint, that the site is compatible with the proposed
improvements, provided that the geotechnical recommendations presented in this report are incorporated
into project plans and followed during construction. Also, long-term human activity within the site can
adversely or positively impact site stability. The proposed development area appears to be marginally
stable under current conditions. It is also our opinion that the slope above the site is currently generally
stable. However, the site is mapped within a geologic hazard area, and recent slope instability has
occurred on the steep slopes above the railroad track. We also encountered evidence of potential past
landsliding within the upper portion of the on -site material in the form of slickensides and low shear
strength. To alleviate potential site instability concerns, project plans indicate that the entire residence
will be supported on drilled piers extending down into the competent material at depth. This is further
described in the Deep Foundations subsection of this report.
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
steep slope to the west. We should be retained to review final project plans prior to construction and to
monitor earthwork and foundation system installation during construction.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75 h Place West
Edmonds, Washington
July 15, 2011
_ NGA File No. 8342B11
Page 8
The residence is planned to be about 64 feet away from the steep slope, and the deck is planned to be
about 58 feet from the slope. Based on our interpretation of the site, it is our opinion that these setback
distances are adequate provided that the recommendations for deep foundations and erosion control
management are followed. We further discuss the setbacks in the Structure Setbacks subsection of this
report.
We understand that the lower floor slab will be designed as a structural slab and will be entirely supported
on deep foundation. For slabs -on -grade and other hard surfaces, such as paved areas or walkways that are
supported on the existing soil, some risk of future settlement, cracking, and maintenance should be
expected. To reduce this risk, we recommend over -excavating a minimum of two feet of the upper soil
from the slab and pavement areas and replacing this material with compacted pit run or crushed rock
structural fill. This recommendations is only for hard surfaces to be supported on grade and does not
apply for the lower floor structural slab. Even with the recommended treatment, some settlement of the
underlying loose material should be anticipated.
The control of surface and near -surface water is very important for the long-term stability of the site and
steep slopes. We highly recommend that temporary and final site grading be designed to direct surface
water away from the structures and away from the steep slope. Final drainage plans have not been
developed at this time, but we understand that all stormwater generated on the site will be collected in
tightlines and transported to the bottom of the slope to the west of the property via a pipe anchored to the
slope. No water should be infiltrated or dispersed within the site. We discuss general site drainage in the
Site Drainage subsection of this report.
— An approximate 6-foot tall block retaining wall is located just to the east of the eastern property line,
directly below the road. It appears that this wall was constructed to support the fill embankment
associated with 75`" Place West. It is our opinion that this wall is unstable and could cause problems on
the property in the future. We recommend that the City of Edmonds be contacted and the removal of this
wall and the replacement with a soldier pile wall be implemented. If this wall cannot be removed, we
recommend that a soldier pile wall be placed to the west of the existing wall. This is discussed further in
the Soldier Pile subsection of this report.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75t' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Page 9
A surficial landslide occurred on the steep slope. It is our opinion that this slide is shallow and should not
affect the residence. However, the landslide should be stabilized as soon as possible to prevent further
damage to the slope. We recommend that erosion control matting be secured to the slope and vegetation
replanted. We provide specific recommendations in the Repairs of Recent Landslide subsection of this
report.
- Though a surficial slide recently occurred on the steep slope, in general, the site currently appears
generally stable with respect to deep-seated movement. However, the site vicinity is mapped within an
- older landslide complex and our explorations encountered evidence of past ground movement. The
potential for landslide and erosion hazards will depend on how the site is graded and how surface water
and near surface water are controlled. We recommend that grading and site drainage plans be subjected
to geotechnical engineering review prior to construction.
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.
We recommend that NGA be retained to review final project plans. 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.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75`h Place West
Edmonds, Washington
July 15, 2011
— NGA File No. 8342B 11
Page 10
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 straw bales should be erected to prevent muddy water from leaving the
site or flowing over the site slopes and the steep slope to the west of the property. Disturbed areas should
be planted as soon as practical and the vegetation should be maintained until it is established. The erosion
potential for areas not stripped of vegetation should be low to moderate. Also, irrigation systems should
not be installed on or near the slope.
-- Protection of the 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 the steep
slope or any portion of sloping ground, such as excavation spoils and soil stockpiles. Trees may be cut
down and removed from the slopes as long as a mitigation plan is developed for maintaining slope
stability, such as the replacement of vegetation for erosion protection. A vegetation cover should be
preserved on the slopes. Replacement of vegetation should be performed in accordance with the City of
Edmonds code. Under no circumstances should water be allowed to concentrate on the slopes. Any
sloping areas disturbed during construction should be planted with vegetation as soon as practical to
reduce the potential for erosion.
Structure Setbacks
Uncertainties related to building along the top of 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 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, the lower the risk of slope failures to impact
the structure. From a geological standpoint, the setback dimension is based on the slope's physical
characteristics, such as slope height, slope gradient, soil type, and groundwater conditions. 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.
• • ,
Revised Geotechnical Engineering Report
Olson Residence
- 15500 — 75t' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Page 11
Based upon the conditions described above, it is our opinion that the potential for shallow sloughing -type
failures and small-scale landslides exist on the steep slopes, as seen with the recent landslide on the site.
This condition is exacerbated where water is present or where the slopes become locally very steep.
Backwasting through sloughing of steep slopes can occur up the slope, such that a loss of ground could
occur. The planned residence will be setback approximately 64 feet from the top of the slope, and the
planned deck will be about 58 feet from the top of slope. These setback distances are adequate; however,
due to the potentially unstable debris found on the site and the history of the area, we have recommended
that the residence be supported on deep foundations in the form of drilled piers. We have recommended
that the piers advance a minimum of 25 feet below the existing ground surface. Loose material should
not be stockpiled in any area between the top of the slope and the residence footprint.
Site Preparation and Grading
Plans for site grading should be devised such that cuts and fills are kept to a minimum. Site preparation
should consist of excavating the residence footprint and driveway areas 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 in any area between the top of the slope and the residence footprint. If the exposed soils are
loose/soft, they should be compacted to a non -yielding condition. Areas observed to pump or weave
during compaction should be over -excavated and replaced with rock spalls. If significant surface water
flow is encountered during construction, this flow should be diverted around areas to be developed and
the exposed subgrade maintained in a semi -dry condition. In wet conditions, the exposed subgrade
should not be compacted, as compaction of a wet subgrade may result in further disturbance of the soils.
A layer of crushed rock may be placed over the prepared areas to protect them from further disturbance.
The site soils are considered extremely moisture sensitive and will disturb easily when wet. We
recommend that earthwork construction take place during periods of extended dry weather, and
suspended during periods of precipitation if possible. If work is to take place during periods of wet
weather, care should be taken during site preparation not to disturb the site soils. This can be
accomplished by utilizing large excavators equipped with smooth buckets and wide tracks to complete
earthwork, and diverting surface and groundwater flow away from the prepared subgrades. Also,
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75t' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Page 12
construction traffic should not be allowed on the exposed subgrade. A blanket of rock spalls should be
used in construction access areas if wet conditions are prevalent. The thickness of this rock spall layer
should be based on subgrade performance at the time of construction. For planning purposes, we
recommend a minimum one -foot thick layer of rock spalls.
Temporary and Permanent Slopes
Temporary cut slope stability is a function of many factors, including the type and consistency of soils,
depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open and the
presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate
a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to
maintain safe slope configurations since he is 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:IV). If groundwater seepage is encountered, we would expect
that flatter inclinations would be necessary. Steeper cuts may be feasible if dense soils are exposed. 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 maintained until established. We should specifically
• • '
Revised Geotechnical Engineering Report
Olson Residence
15500 - 75`h Place West
Edmonds, Washington
July 15, 2011
_ NGA File No. 8342B 11
Page 13
review all plans for grading on this project. We do not recommend grading on steep slopes, or placing
irrigation systems near the slopes.
Foundation Support
Current plans indicate that the entire residence will be supported on 16- to 24-inch reinforced concrete
piers, extending a minimum of 25 feet below existing ground surface.
-- An open -hole drilling method will likely be feasible based on our field observations, however, if caving
conditions are encountered, pile casing will be required. The holes should be cleaned of any slough or
-- water prior to pouring concrete. We recommend that the concrete be readily available on site at the time
of drilling. The holes should not be left open for any extended period of time, as sloughing debris and/or
groundwater seepage into the excavations may hamper pier installation.
For piers installed successfully as described above, we recommend using a design axial compression
capacity of 25 and 40 tons for 16- and 24-inch piers, respectively. Lateral resistance on the piers could be
_ calculated based on an equivalent fluid density of 200 pounds per cubic foot (pcf) applied to two pile
diameters. The upper 15 feet should be neglected for the purpose of calculating the lateral resistance.
Structural Fill
General: Fill placed beneath foundations, pavements, and other settlement -sensitive structures, or behind
retaining walls should be placed as structural fill. Structural fill, by definition, is placed in accordance
with prescribed methods and standards and is monitored by an experienced geotechnical professional or
soils technician. Field monitoring procedures would include the performance of a representative number
of in -place density tests to document the attainment of the desired degree of relative compaction. The
area to receive the fill should be prepared as outlined in the Site Preparation and Grading subsection of
this report. Sloping areas to receive fill should be benched prior to fill placement. The benches should be
level and at least four feet wide.
Materials: Structural fill should consist of a good quality, granular soil, free of organics and other
deleterious material and be well graded to a maximum size of about three inches. All-weather fill should
contain no more than five -percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing
NELSON GEOTECHNICAL ASSOCIATES, INC.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75`h Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Page 14
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.
Retaining Walls
We understand that retaining walls up to nine feet high will be incorporated into project plans. We
recommend that retaining walls be kept as short as possible.
The lateral pressure acting on subsurface retaining walls is dependent on the nature and density of the soil
behind the wall, the amount of lateral wall movement which can occur as backfill is placed, wall drainage
conditions, the inclination of the backfill, and other possible surcharge loads. For walls that are free to
yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be
less than if movement is limited by such factors as wall stiffness or bracing (at -rest condition). We
recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces be designed
using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 40 pcf
for yielding (active condition) walls, and 60 pcf for non -yielding (at -rest condition) walls.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75t' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Page 15
These recommended lateral earth pressures are for a drained granular backfill and are based on the
assumption of a horizontal ground surface behind the wall for a distance of at least the subsurface height
of the wall, and do not account for surcharge loads. Additional lateral earth pressures should be
considered for surcharge loads acting adjacent to subsurface walls and within a distance equal to the
subsurface height of the wall. This would include the effects of surcharges such as traffic loads, floor slab
and foundation loads, slopes, or other surface loads. Also, hydrostatic and buoyant forces should be
included if the walls could not be drained. We could consult with the structural engineer regarding
additional loads on retaining walls during final design, if needed.
All wall backfill should be well compacted; however, care should be taken to prevent the buildup of
excess lateral soil pressures, due to over -compaction of the wall backfill. This can be accomplished by
placing wall backfill in thin loose lifts and compacting it with small, hand -operated compactors within a
distance behind the wall equal to at least one-half the height of the wall. The thickness of the loose lifts
should be reduced to accommodate the lower compactive energy of the hand -operated equipment.
Retaining wall foundations should be supported on a minimum of two feet of rock spalls to reduce the
potential for differential settlement of the walls. The active pressure on the wall can be resisted by
friction on the bottom of the wall footing and passive resistance on the below -grade portion of the footing.
We recommend using a design soil bearing pressure of no more than 2,000 pounds per square foot (psf)
along with a friction coefficient and passive resistance of 0.35 and 200 pcf, respectively.
Permanent drainage systems should be installed for retaining walls. Recommendations for these systems
are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to
evaluate the proposed wall drain backfill material and drainage system installation.
Structural Slab
As mentioned earlier, the lower floor slab will be designed as a structural slab fully supported on deep
foundations. We recommend that slabs be underlain by at least six inches of free -draining gravel with
less than three percent by weight passing the Sieve #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
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75"' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B 11
Page 16
placed over the capillary break material. An additional 2-inch-thick moist sand layer may be used to
cover the vapor barrier. This sand layer may be used to protect the vapor barrier membrane and to aid in
curing the concrete; however, this sand layer is optional and is intended to protect the vapor barrier
membrane during construction.
Soldier Pile Wall
As mentioned previously, an approximate 6-foot tall block retaining wall is located just to the east of the
eastern property line, but not on the project site. It appears that this wall was constructed to support the
Lunds Gulch Road. It is our opinion that this wall is unstable and could cause problems on the property
- in the future. We recommend that this wall be removed or stabilized using a soldier pile wall. We
recommend that the new soldier pile wall be placed to the west of the existing wall to protect the Olson
property against potential failure of the block wall.
The soldier pile wall should extend roughly from the northern property line to the southern extent of the
existing block wall. A solider pile wall typically consists of a series of steel H-beams placed vertically at
a certain distance from one another (typically six to ten feet). The beams are usually placed in drilled
shafts that are filled with concrete or grout. The concrete shafts are typically embedded below the bottom
of the planned excavation a distance equals one to two times the height of the cut to be shored, if tie-
backs are not used. The steel beams are extended above finished ground surface to provide shoring
capabilities for the cut. The beams are typically spanned by pressure treated timber lagging. The H-beam
size, shaft diameter, shaft embedment, and pile spacing are dependent on the nature of the soils
anticipated in the cut and at depth, cut height, drainage conditions, the need for tie -backs, and the final
geometry.
The soldier pile wall should be designed by an experienced structural engineer licensed in the State of
Washington. The wall should be designed for an active pressure acting on the piles and lagging for
design of the soldier piles and should be calculated based on a triangular pressure distribution equivalent
to that exerted by a fluid with a density of 50 pcf.
The above loads should be applied on the full center -to -center pile spacing above the base of the exposed
portion of the wall. These loads could be resisted by passive resistance acting on the below -grade portion
Revised Geotechnical Engineering Report
Olson Residence
_ 15500 — 75 h Place West
Edmonds, Washington
July 15, 2011
_ NGA File No. 8342B 11
Page 17
of the piles. A 50 percent reduction of this value can be applied for the purpose of designing the wall
lagging. The passive resistance could be calculated based on a 100 pcf equivalent fluid density acting on
two effective pile diameters below the base of the exposed portion of the wall. This value incorporates a
factor of safety of 2. The below -grade portion of the wall should not be shorter than twice the wall stick-
up height.
The soldier pile wall should be installed by a shoring contractor experienced with this type of system.
Although we anticipate that an open -hole drilling method will be adequate for installing the soldier piles
in the on -site soils, the shoring contractor should be capable of casing the holes as sloughing and/or water
-- seepage may be encountered. It might be prudent to perform one or more "test" holes to confirm
installation conditions prior to finalizing work plans. Any sloughing or water that may collect in the
drilled holes should be removed prior to pouring grout. Grout should be readily available on site at the
time the holes are drilled. The holes should not be left open for any length of time, as that may increase
the potential for caving and water seepage to impact wall installation.
If groundwater seepage is encountered, we recommend that the concrete be tremied from the bottom of
the excavations to displace the groundwater to the surface. Extra Portland Cement may also be placed in
the bottom of the excavations to reduce the effects of seepage. The spoils from the soldier pile
excavations are expected to be moisture -sensitive materials and should be removed from the site. We
should be retained to monitor on site activities during the soldier pile wall installation on a full-time basis.
The wall should be lagged using pressure -treated timber or concrete panels. Adequate gaps should be
maintained between the lagging elements to allow water flow through the face of the wall. Also, all wall
backfill should consist of 2-inch clean drain rock. It is imperative that water not be allowed to pool
behind the wall, therefore extreme care should be taken not to contaminate the drain rock with silt or
organics. In wet conditions, it might be necessary to use a filter fabric along the back of the drainage
-- layer.
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
NELSON GEOTECHNICAL ASSOCIATES, INC.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75t` Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B11
Page 18
cracking, we recommend that the upper two feet of the existing material be removed and replaced with
structural fill. 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. If the existing soil is left in place,
the pavement section should be thickened to further reduce the effects of settlement.
Repairs of Recent Landslide
For the landslide that was recently experienced on the steep slope on the property, we recommended
that the exposed soil be covered with heavy duty erosion control matting such as Tensar C350 Turf
Reinforcement Mat, or equivalent. Prior to placing the matting, any areas of loose soils should be
- removed to expose dense native soil. The matting should be staked at the top of the slope with two to
three rows of two- to three-foot long metal rebar that is either bent at the end or has a metal "T"
welded to the end. The mat should be laid flush to the slope and staked to the exposed soil on the
slope a minimum of every five feet. The slide debris that accumulated behind the small retaining wall
should be cleaned out. After the matting netting is placed, we recommended that deep-rooted
vegetation be planted on the slope and grass seed be planted to re-establish vegetation growth. All
surface water flow should be permanently directed away from the slide area. We should be retained to
monitor the repairs of the landslide.
Site Drainage
Surface Drainage: The finished ground surface should be graded such that stormwater is directed to an
appropriate stormwater collection system. Water should not be allowed to collect in any area where
footings, slabs, or retaining walls are to be constructed. Final site grades should allow for drainage away
from the structure and away from the steep 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.
Revised Geotechnical Engineering Report
Olson Residence
15500 —'75`h Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B11
Page 19
We recommend that stormwater generated on the site, including roof downspouts, footing drains,
pavement and yard drains, and water flow from the road, be tightlined to the bottom of the slope to the
west. This should entail directing all collected runoff into a main catch basin placed about 15 feet away
from the top of the steep slope, from which a 6- to 8-inch diameter HDPE pipe should be extended to the
back of the existing wall along the BNSF right-of-way. A concrete collar should be placed around the
pipe between the catch basin and top of the slope to help anchor the pipe. The pipe should be laid on the
slope surface but should be anchored using T-posts and metal straps. The pipe should end with a
perforated Tee section approximately eight feet long that is capped on both ends and embedded in the
crushed rock found behind the existing wall.
Subsurface Drainage: If groundwater is encountered during construction, we recommend that the
- contractor slope the bottom of the excavations and collect water into ditches and small sump pits where
the water can be pumped out of the excavations and routed into an appropriate outlet.
We recommend the use of footing drains around the planned structure and behind retaining walls.
Footing drains should be installed at least one -foot below planned finished floor elevation. The drains
should consist of a minimum four -inch -diameter, rigid, slotted or perforated, PVC pipe surrounded by
free -draining material, such as washed rock, wrapped in a filter fabric. We recommend that an 18-inch-
wide zone of clean (less than three -percent fines), granular material be placed along the back of the walls
above the drain. Washed rock is an acceptable drain material, or drainage composite may be used instead.
The free -draining material should extend up the wall to one -foot below the finished surface. The top foot
of backfill should consist of low permeability soil placed over plastic sheeting or building paper to
minimize the migration of surface water or silt into the footing drain. Footing drains should discharge
into tightlines leading to an appropriate collection and discharge point with convenient cleanouts to
prolong the useful life of the drains. Roof drains should not be connected to footing drains.
-- Roof drains should also be installed around the site structures. The 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
NELSON GEOTECHNICAL ASSOCIATES, INC.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75 h Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B11
Page 20
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. George Olson and his agents, for use in the planning and design of
the development planned on this site only. The scope of our work does not include services related to
construction safety precautions and our recommendations are not intended to direct the contractors'
methods, techniques, sequences, or procedures, except as specifically described in our report for
consideration in design. There are possible variations in subsurface conditions between the explorations
and also with time. Our report, conclusions, and interpretations should not be construed as a warranty of
subsurface conditions. A contingency for unanticipated conditions should be included in the budget and
schedule.
We recommend that we be retained to review final project plans and provide consultation regarding
specific structure placement, site grading, foundation support, and drainage. We also recommend that
NGA be retained to provide monitoring and consultation services during construction to confirm that the
conditions encountered are consistent with those indicated by the explorations, to provide
recommendations for design changes should the conditions revealed during the work differ from those
anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with
contract plans and specifications. We should be contacted a minimum of one week prior to construction
activities and could attend pre -construction meetings if requested.
All people who own or occupy homes on or near hillsides should realize that landslide movements are
always a possibility. The landowner should periodically inspect the slope, especially after a winter storm.
If distress is evident, a geotechnical engineer should be contacted for advice on remedial/preventative
measures as soon as possible. The probability that landsliding will occur is substantially reduced by the
proper maintenance of drainage control measures at the site (the runoff from the impervious surfaces
should be led to an approved discharge point). Therefore, the homeowner should take responsibility for
performing such maintenance.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75t' Place West
Edmonds, Washington
July 15, 2011
NGA File No. 8342B11
Page 21
Within the limitations of scope, schedule, and budget, our services have been performed in accordance
with generally accepted geotechnical engineering practices in effect in this area at the time this report was
prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are
a means to identify and reduce the inherent risks to the owner.
•••
NELSON GEOTECHNICAL ASSOCIATES, INC.
Revised Geotechnical Engineering Report
Olson Residence
15500 — 75t` Place West
Edmonds, Washington
July 15, 2011
_ NGA File No. 8342B 11
Page 22
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.
do Bala Do e-Alah y
- Project Geologist
EXPlR�S
Khaled M. Shawish, PE
Principal
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COARSE-
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GRAVEL
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SC
CLAYEY SAND
FINE -
SILT AND CLAY
INORGANIC
ML
SILT
-
GRAINED
LIQUID LIMIT
LESS THAN 50 %
CL
CLAY
ORGANIC
OL
ORGANIC SILT, ORGANIC CLAY
SOILS
SILT AND CLAY
INORGANIC
MH
SILT OF HIGH PLASTICITY, ELASTIC SILT
MORE THAN 50 %
PASSES
NO. 200 SIEVE
LIQUID LIMIT
50 % OR MORE
CH
CLAY OF HIGH PLASTICITY, FLAT CLAY
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 Moist - Damp, but no visible water.
is based on ASTM D 2488-93.
Wet - Visible free water or saturated,
3) Descriptions of soil density or usually soil is obtained from
consistency are based on below water table
interpretation of blowcount data,
visual appearance of soils, and/or
_
test data.
Project Number
83421311
Olson Residence
NELSON GEOTECHINICAL
%ASSOCIATES, INC.
No.
Date
Revision
By
CK
1
3/25/11
Original
DPN
BD
Soil Classification Chart
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Figure 4
17311-135th Ave. NE, A5W S-t—d h C—ty (425) 337-1669
W—f—Pa. WA 98072 We tcfi.tChe Fan(5W) 665-7696
(425) 466-16691 Fax 481-2510 vn5w.neiwngeotnch.com
L
nnnrnYtrr,ate Ground Surface Elevation: —96 feet
Soil Profile
Description
BORING LOG
Sample Data
a�
c w
m �-76
�jJ U� mV �JEL
(D
3rown-gray fine to medium sand with silt and trace gravel
2
every loose,moist)
SP-SM
3ray, silty fine to medium sand with silt and trace gravel
16
medium dense, moist)
SM
18
_LGray, silt with fine sand, (very stiff, moist to wet)
11
nottled and contains slickensides (Slide Plane???)
ML
Blue -gray silt with trace fine sand (very stiff, moist)
20
Contains some slickensides
22
1
-
�=
35
ML
r
40
�r
66
-with interbedded coarse sand
a
79
1Boring terminated below existing grade at 26.5 feet on
10/28/10. Groundwater seepage was not encountered.
Penetration Resistance
(Blows/foot - )
10 20 30 40 50
Moisture Content
(Percent - )
10 20 30 40 50
rn
Piezometer
N
Installation -
Z
Ground Water
Data
9
(Depth in Feet)
co
J
5
m
15
... ... I ........ .I ......... I ......... I ......... I .... E...I F 25
0
LEGEND i� Solid PVC Pipe Concrete M Moisture Content
Slotted PVC Pipe Bentonite A Atterberg Limits
Depth Driven and Amount Recovered G Grain -size Analysis
1 with 2-inch O.D. Split -Spoon Sampler11= Monument/ Cap Native Soil DS Direct Shear
to Piezometer PP Pocket Penetrometer Readings, tons/ft
Depth Driven and Amount Recovered * Liquid Limit Silica Sand p Sample Pushed
with 3-inch Shelby Tube Sampler + Plastic Limit V Water Level T Triaxial
1 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.
NELSON GEOTECHNICAL No. Date Revision By cK
Project Number
8342BII Olson Residence A, ASSOCIATES, INC.
1 3/25/11 Original LSB KMS
Boring Log GEOTECHNICAL ENGINEERS Sc GEOLOGISTS
Figure 5 SrwKomish C—ty (425) 339-1669
17311-135ih Ava. 98072 A-500 VV n tchee/C"el (509)665-7696
Pane 1 of 1 W486-1 69,/F 481-2
(425) 466-1669 / Fax 481-2510 wr+/.nalwrgeotech.tom
BORING LOG 0
m
®2 co
.0
N
I T
L �
Approximate Ground Surface Elevation: —79 feet
Penetration Resistance 0' J
Soil Profile Sample Data (glows/foot - ) Piezometer
10 20 30 40 50 50+ H Installation -
t I Ground Water
o °' o °' Moisture Content o Data
Description n o o Q o E (Percent -) o (Depth in Feet)
m U O 0 10 20 30 40 50 50+ @
l C7 co
3rown-gray silty, fine to medium sand with silt and trace
2
gravel (medium dense, moist)
'
16
.. •._. SM
5
...................................................
5
22
-becomes with silt lenses, and moist to wet
16
Gray silt with trace fine sand (stiff, moist)
Plane???)
bra
14
10
...................................................
10
lottled and contains slickensides (Slide
s ML
1
�r
..................
-15
(Tan fine sandy silt (very hard, moist)
88
-tclean fine sand on top of sample
MIL
1
2
..............
20
becomes gray, laminated, with interbedded fine sand
87-11"
layers �oring
terminated below existing grade at 21.5 feet on
10/28/10. Groundwater seepage was not encountered.
1
25
1
25
.........................
.........................
LEGEND j�
Solid PVC Pipe Concrete M Moisture Content
Depth Driven and Amount Recovered
A Atterberg Limits
Slotted PVC Pipe Bentonite G Grain -size Analysis m
with 2-inch O.D. Split -Spoon Sampler
1
Monument/ Ca p Native Soil DS Direct Shear
Readings, tons/ft S
Depth Driven and Amount Recovered �'c
to Piezometer PP Pocket Penetrometer
q Silica Sand p Sample Pushed o
Liquid Limit p a
with 3-inch Shelby Tube Sampler I
Plastic Limit Water Level T Triaxial o
1 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
of other times and locations. We cannot accept responsibility
for the use or interpretation by others of information presented on this log.
arepresentative
Project Number
NELSON GEOTECHNICAL.
No.
Date
Revision
By
CK ON
C)
8342B11
Olson Property
ASSOCIATES, INC.
N A
1
3/25111
Original
LSB
KMS o
Boring Log
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Figure 6
_ S, ho,nlsh County(425) 339-1669
17 Woad 411a. WA 96072� Wa t=/CKaln(509) 665-7696
IoAR.1RR9
C
a
_'� /Gar dAl.�Stn WNN.�BISOMeOMch.COT 7
LOG OF EXPLORATION
DEPTH (FEET) USC SOIL DESCRIPTION
HAND AUGER ONE
0.0 - 0.5 TOPSOIL
- 0.5 - 3.5 ML BROWN -GRAY, SANDY SILT WITH TRACE ORGANICS AND SILT LAYERS
(SOFT, MOIST TO WET)
3.5-4.0 CL BLUE -GRAY CLAY WITH SLICKENSIDES AND MOTTLED (SOFT, MOIST)
SAMPLES WERE COLLECTED AT 2.0, 3.5, AND 4.0 FEET
LIGHT GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 3.0 FEET
HAND AUGER CAVING WAS NOT ENCOUNTERED
HAND AUGER WAS COMPLETED AT 4.0 FEET ON 3/30111
HAND AUGER TWO
0.0 - 0.5 TOPSOIL
0.5 - 2.5 ML BROWN -GRAY, SANDY SILT WITH SILT LAYERS AND ORGANICS
(SOFT, MOIST TO WET)
2.5 - 3.5 ML GRAY, SANDY SILT (VERY STIFF, MOIST)
SAMPLE WAS COLLECTED AT 3.5 FEET
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
HAND AUGER CAVING WAS NOT ENCOUNTERED
HAND AUGER WAS COMPLETED AT 3.5 FEET ON 3/30/11
HAND AUGER THREE
0.0 - 0.5 TOPSOIL
0.5 - 2.5 ML BROWN -GRAY, SANDY SILT WITH SILT LAYERS AND ORGANICS
(SOFT, MOIST TO WET)
2.5 - 3.5 ML GRAY, SANDY SILT (VERY STIFF, MOIST)
SAMPLES WERE NOT COLLECTED
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
_ HAND AUGER CAVING WAS NOT ENCOUNTERED
HAND AUGER MET REFUSAL ON A ROOT AT 3.5 FEET ON 3/30/11
LSB:DPN NELSON GEOTECHNICAL ASSOCIATES, INC.
FILE NO: 83421311
FIGURE 7