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SUBSURFACE E~CPLORATION AND
GE~TECHNiCAL ENGINEERING REPORT
Eastgard Property, 270 Harring on Drive
Jefferson County, Washington
.Prepared for: Tom Eastgard
Project No. 060266-002-01 • January 17, 2007
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Juiy 11, 2007
Mr. Tom Eastgard
3967 El Cimo Lane
Bainbridge Island, Washington 9$1110
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Subject: Geotechnical Review of Revised Catchment Wall Location
270 Harrington Drive
Jefferson County, Washington.
Project No. 060266-003-01
Reference: SUBSURFACE EXPLORATIONAND GEOTHCHNICAL ENGINEERING
REPORT, Eastgard Property, 270 Harrington Drive, Jefferson County,
Washington, dated January 17, 2007, by Aspect Consulting, LLC
Dear Mr: Eastgard:
We have received a request from your architect to review the current design location of the
catchment wall. Due to the setbacks on the opposite side of the house and the large designed
thickness ofthe catchment wall, the exterior of the wall slightly encroaches into the setback at
one corner from of the house by 2 feet. Within approximately 131inear feet, the wall meets the
setback and the remaining two-thirds of the wall then exceeds the minimum setback to a
maximum of approximately 2 feet... Given that the average of the setback is greater than 15 feet,
Aspect Consulting believes that this minor intrusion of the- structural wall does not
significantly deviate from the overall geotechncal setback recommendation for the catchment
wall,. and that the wall will perform its intended function:
We are pleased to have this continued opportunity to work with you. If you have any
questions, please do not hesitate to call me at (206} 7$0-7720.
Sincerely,
Aspect consulting, LLC
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Join L. Peterson, PE
Associate Geotechnical Engineer
jpeterson@aspectconsulting.com
cc: Daniel Dennon, Roger Katz & Associates: (via. a-mail)
W:1 GEOTECH1060266 Eastgard ReconlwaR placement Review Ltr.dce
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SUBSURFACE EXPLORATION AND
GEOT~ECHNICAL ENGINEERING REPORT
Eastgard Property, 270 Harrington Drive
Jefferson County, Washington
Prepared for: Torn Eastgard
Project No. 060266-002-01 • January 17, 2007
Aspect Consulting, LLC
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James A. Peterson, PE ' John L. Peterson, PE
Project Geotechnical Engineer Associate Geotechnical Engineer
apeterson@aspectconsulting.com jpeterson@aspectconsulting.com
W:\ GEOTECH\060266 Eastgard Recon\Eastgard Geotech Report.doc
ASPECT CONSULTING
Contents
1 Project Information .........:............................................................................1
1.1 Introduction ................................................................................................1
1.1.1. Purpose and Scope ..............................................................................1
1.1.2 Authorization ............................................................................:...........1
1.2 Project and Site Description ............:............ ......................1
........................
1.2.1 Slope Conditions .................................................................................. 2
1.3 Subsurface Exploration .............................................................................. 2
1.3.1 Exploration Borings .............................................................................. 2
1.4 Subsurface Conditions ~ .............................................................................. 3
1.4.1 Stratigraphy .............................~...........................................................:.3
1.4.2 Hydrology...........i........- ............................:............................................3
''°° 2 Geologic Hazards and Mitigation ...............................................................5
2.1 Seismic Hazards and Recommended Mitigation ......................................
2.1.1 Landslides and Liquefaction ............................................................... .. 5
.. 5
2.1.2 Ground Motion ............................:....................................................... ..6
- 2.2 Erosion Hazards and Mitigation ............................................................... ..6
2.2.1 Mitigation ...................................................:........................................ ..6
2.3 . Landslide. Hazards and;Mitigation ............................................................ .. 7
2.3.1 Rotational Type Landslides ....................................................,........... .. 7
2.3.2 Surficial or Debris Landslides ............................................................. .. 7
.~:~. 3 Design Recommendations ........................................................................ ..8
3.1 Site Preparation ......................................................................................... 8
3.1.1 Clearing and Filling ..............._...................................................:......... ..8
3.1.2 Site Disturbance ................................................................................ ..
3.2 8
Structural Fill ..............................................................................................
3.3 Foundations ................:.............................................................................. 9
__ 3:3:1 _ Spread Footings.........:.:::.:.:::.:. .....~.........:. 9
3.4 Floor Support ........................................................................................... 10
-- 3.5 Catchment Wall Recom'mendation ........................................................... 10
3.5.1 Catchment Wall Criteria ...................................................................... 10
3.6 Drainage Considerations ....................:..................................................... 11
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3.7
Project Design and Construction Monitoring ............................................
11
Limitations .........................................................................................................12
-, PROJECT NO.060266-002-01 • JANUARY 17, 2007
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List of Figures
1 Site Location Map
2 Site and Exploration Plan
List of Appendices
A Boring Logs
ii PROJECT NO. 060266-002-01 • JANUARY 17, 2007
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1 Project Informations
1.1 Introduction
This report presents the results of our subsurface exploration and geotechnical
engineering study for the Eastgard property located at 270 Harrington Drive, on the
eastern shoreline of the Toandos peninsula in Jefferson County, Washington. The
location of the property is shown on the Site Location Map, Figure 1. The approximate
locations of the subsurface explorations accomplished for this study are presented on the
Site and Exploration Plan, Figure 2: In the event that any changes in the nature, design or
_ location of the structure are planned, the conclusions and recommendations contained in
this report should be reviewed arnd verified, or modified, as necessary.
1.1.1 Purpose and Scope
The purpose of this study was to provide geotechnical design recommendations to be
utilized in the design and development of a proposed new house at the site, with
appropriate landslide remediation/mitigation measures. Our study included reviewing
available geologic literature, drilling two exploration borings, and performing geologic
studies to assess the type, thickness, distribution and physical properties of the subsurface
sediments and shallow groundwater conditions. Geotechnical engineering studies were
conducted to formulate retaining, wall and drainage recommendations. This geotechnical
report summarizes our current field work and offers geologic hazard mitigation and
geotechnical engineering recommendations based on our present understanding of the
project.
1.1.2 Authorization
Written authorization to proceed with this study was granted by Mr. Tom Eastgard on
November 17, 2006.Our study was accomplished in general accordance with our scope
of work proposal dated November 15, 2006.
1.2 Project and Site Description
.:,
This report was completed-with ~n understanding of the project based on a site-plan
provided by Mr. Eastgard, and by our discussions with Mr. Eastgard. At the time of our
exploration program, the site was occupied by asingle-family, manufactured residence
and a detached garage. Preliminary plans call for the removal of the existing structures
and construction of a new house in the same general area, adjacent to the toe of the slope.
The property is situated on the waterfront along Hood Canal. The site is rectangular in
.plan, encompasses two tax parcels, with property dimensions of approximately 200 feet
along the southwest/northeast property lines, and approximately 1,000 feet along the
-. southeast/northwest property lines. The upland portion of the site consisted of northwest-
to-northeast-facing hillside, with',inclinations ranging from approximately 0.75H:1 V
(Horizontal:Vertical) to SH:1 V, with a typical slope angle on the order of 1.2H:1 V above
PROJECT N0.060266-002-01 • JANUARY 17, 2007
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the proposed house. The site was bordered to the northwest, southeast and southwest by
private residential properties, and by the low tide line of Hood Canal to the northeast.
The existing structures were located in the bottom of a flat to gently sloping ravine floor
in the northwest portion of the property. Vegetation around the existing residence
consisted primarily of grass lawn and landscaped shrubbery, with some cedar trees in the
upslope, southwestern portion of the ravine.
9.2.1 Slope Conditions
The site consists of a steeply sloping southwestern portion and a flat to gently sloping,
lower, northeastern portion containing the existing and proposed house location.
Average slope inclination for the steep slope was on the order of 1.2H:1 V. Overall
vertical relief of the slope above the proposed house site was on the order of 50 feet. The
slope contained fir, cedar, maple, and alder trees with a dense understory of ferns, berry
bushes, and other shrubs. Average slope inclinations of the lowest portion slopes near the
proposed house footprint were on the order of 1 H:1 V, with one area at the toe of the
slope near the existing garage cut to a maximum height of approximately 15 feet at a
slope angle of approximately O.SH:1 V. The cut was reportedly made more than 7 years
previously, and shows signs of only surficial sloughing of the face.
1.3 Subsurface Exploration
Our field study included drilling two exploration borings, one in the vicinity of the
proposed house footprint and one at the top of slope above the proposed house footprint.
The various types of sediments, as well as the depths where characteristics of the
sediments changed, are indicated on the exploration logs presented in Appendix A of this
report. The depths indicated on the logs where conditions changed may represent
gradational variations between sediment types. Changes logged between sample intervals
in our borings were interpreted. Soils were classified in general accordance with the
American Society for Testing and Materials (ASTM) D-2488, "Standard Practice for
Description and Identification of Soils (Visual and Manual Procedure)". Our explorations
were approximately located in the field by measuring from existing site features shown
on the plan provided by Mr. Eastgard.
9.3.1 Exploration Borings
On January 2, 2007, two exploration borings (EB-1 and EB-2) were completed within the
project site. -The borings were completed by advancing a 3 /a-inch inside-diameter, - - - -- -
hollow-stem auger with atrack-mounted drill rig operated under subcontract to Aspect
Consulting. The boring depths were 60.9 feet in EB-1 and 20.8 feet in EB-2. The boring
logs are presented in Appendix A of this report. The approximate location of each boring
is shown on the Site and Exploration Plan, Figure 2. Samples were obtained using the
Standard Penetration Test (SPT). This involves driving a 2-inch outside-diameter split-
barrel sampler a distance of 18 inches into the soil with a 140-pound hammer free-falling
from a distance of 30 inches. The number of blows for each 6-inch interval is recorded
and the number of blows required to drive the sampler the final 12 inches is used to
calculate the Standard Penetration Resistance ("N") or blow count. Field variations in the
test method, if they occur, are incorporated into the "N" value calculation. The resistance,
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PROJECT NO.060266-002-01 • JANUARY 17, 2007
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or N-value, provides a measure of the relative density of granular soils or the relative
consistency of cohesive soils; these values are shown on the attached boring logs.
1.4 Subsurface Conditions
Subsurface conditions at the project site were inferred from the field explorations
accomplished for this study, visual reconnaissance of the site and vicinity, and review of
applicable geologic literature.
As shown on the boring logs, a thin layer of topsoil and grass was encountered in both
borings. The topsoil layer was underlain by medium dense to very dense, glacially
consolidated sand and gravel with varying amounts of silt. These sediments were
interpreted as pre-Fraser age, undifferentiated sediments. These sediments were
encountered to the total explored depths of 60.9 feet in EB-1 and 20.8 feet in EB-2. The
following section presents more detailed subsurface information organized from the
upper (youngest) to the lower (oldest) sediment types.
1.4.1 Stratigraphy
Topsoil and Grass
Topsoil and grass were encountered in both borings, to depths of 0.3 foot and 1 foot,
respectively, in EB-1 and EB-2. These soils consisted of loose to medium dense, organic-
rich, silty sand and gravel.
Pre-Fraser Undifferentiated Sediments
Intact, pre-Fraser age undifferentiated sand and gravel deposits were encountered in both
borings. This stratum continued to the entire depth explored in each boring. The soil
consisted of stratified layers of very dense, light brown, reddish-brown and gray, silty
sand and gravel. This stratum can be seen in the driveway road cut upslope of the
proposed house and in the toe of the slope adjacent to the existing garage. These
sediments appeared to be in-place and appear to have been largely unaffected by past
slide activity.
This observed geologic stratum conforms with the published geologic mapping of the
area as shown on the Geologic Map of Surficial Deposits in the Seattle 30'x60'
Quadrangle, Washington, by Yount and Minard, 1993.
..1.4.2. -Hydrology
Groundwater was encountered in both borings at the time of our field study. The depth to
groundwater in the exploration borings was estimated at the time of drilling and ranged
from ground surface in EB-2 to approximately 54 feet in EB-1. The groundwater in EB-2
was the result ofnear-surface saturation in the flat area around the existing house, and
occurred from ground surface to ~ depth of about 1 foot. Below 1 foot samples were
moist. The presence of perched groundwater in EB-1 was inferred from drill action and
wet cuttings returning to the surface from approximately 33 to 34 feet. Additional wet
soil samples were noted from a depth of approximately 54 feet to the bottom of EB-1;
this depth roughly coincides with.. small seeps within discrete sandy seams in the lower
portion of the exposed slope face near the existing garage. Note that these borings were
PROJECT N0.060266-002-01 • JANUARY 17, 2007 3
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performed after an extremely wet November and December and reflect high groundwater
conditions.
Increased groundwater volumes and seepage are a direct result of precipitation. In
addition to precipitation rates and duration, fluctuations in groundwater levels will occur
due to the time of the year, site usage, and other factors such as off-site usage and water
supply systems in the area. Seepage may also occur at random depths and locations in
relatively clean sandy or gravelly seams within the slope.
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4 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 4
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2 Geologic Hazards and Mitigation
The following discussion of potential geologic hazards is based on the geologic, slope,
and groundwater/surface water conditions as observed and discussed herein. The
discussion will be limited to seismic, erosion and landslide hazards.
2.1 Seismic Hazards and Recommended Mitigation
The nearest known, active fault Mace to the project is the Seattle fault, although other
north-south trending fault structures are likely located in the Hood Canal region that have
not been fully characterized. Recent studies by the U.S. Geological Survey (e.g., Johnson
et al., 1994, Origin and Evolution of the Seattle Fault and Seattle Basin, Washington,
Geology, v. 22, p.71-74 and Johnson et al., 1999, Active Tectonics of the Seattle Fault
and Central Puget Sound Washington-Implications for Earthquake Hazards, Geological
Society ofAmerica Bulletin, July,1999, v. 111, n. 7, p. 1042-1053) suggest that the trace
of an east-west trending thrust fault may project approximately 10 miles southeast of the
project site in the vicinity of Bremerton. The trace of this fault can be seen south of
Blakely Harbor on Bainbridge Island. According to the U.S. Geological Survey (IJSGS)
studies, the latest movement of this fault was about 1,100 years ago, resulting in about 20
feet of surficial displacement. This displacement can presently be seen in the form of
raised, wave-cut beach terraces along Allci Point in West Seattle and Restoration Point at-
the south end of Bainbridge Island. The recurrence interval of movement along these
fault systems is still unknown, although it is hypothesized to be on the order of several
thousand years. Due to the suspected long recurrence interval, the distance from the fault,
the potential for surficial ground rupture as a result of faulting is considered low during
the expected life of the structure.
2.7.7 Landslides and Liquefaction
Seismically Induced Landslides
A site specific seismic analysis was beyond the scope of this study and was not
performed. However, the available data from the USGS Earthquake Hazards. site was
obtained in lieu of a specific site study. This value takes into account attenuating factors
associated with the distance of the site from known active fault structures in the area.
Aspect Consulting applied the peak ground acceleration and conservative estimates of the
index properties of the site soil to a general slope stability analysis of the slope across the
site. The analysis was performed using the generalized infinite slope equation, using a
code-based ground acceleration of 0.34g as provided for in Chapters 16 and 18 of the
__ 2003 International Building Cody (IBC).. Factors of safety of 1.25 and 1.15 were obtained
for static conditions and earthqua~Ce conditions, respectively, using the code-based
earthquake.
PROJECT N0.060266-002-01. • JANUARY 17, 2007
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Liquefaction
Due to the high SPT "N" values and/or silt content of the soils, site liquefaction potential
is low.
2.1.2 Ground Motion
Based on the site stratigraphy and visual reconnaissance of the site, it is our opinion that
earthquake damage to the proposed structure founded on a suitable bearing stratum would
likely be caused by the intensity and horizontal ground acceleration associated with the
event. We understand that structural design of the building will follow the 2003 IBC
standards and take into consideration stress caused by seismically-induced earth shaking.
The USGS National Seismic Hazard Map International indicates that the project site
should be assumed to undergo a peak horizontal ground acceleration of 0.57g. Using the
2003 IBC criteria, the site would be characterized by a Seismic Site Class C. The
mapped, maximum considered earthquake spectral response accelerations for short period
(SS) = 1.26g; and for 1-second period (S1) = 0.46g. Site coefficients for this site are Fa =
1.0, F,, = 1.3. The maximum considered earthquake spectral response accelerations
adjusted for site class effects are Sds = 0.84g, Say = 0.41g.
2.2 Erosion Hazards and Mitigation
The soils encountered have a moderate erosion potential where these soils will be
exposed during. construction. The erosion risk increases on sloped areas, whether natural
or excavated during construction. Areas outside of the proposed construction area have
low erosion potential due to the well-developed vegetative cover. Only the areas
necessary for construction should be stripped of vegetation, however, trees which
represent a danger to the structure should be removed.
2.2.1 Mitigation
To mitigate and reduce the erosion hazard and potential for off-site sediment transport,
we recommend the following:
• Surface water should not be allowed to flow across the site over unprotected surfaces.
All runoff water should be tightlined away from the slopes to an appropriate storm-
watercollection facility: Under no circumstances should surface water be allowed to
flow over the top of the slopes.
___
• All stormwater from impermeable surfaces, including driveways and roofs, should be
tightlined to a suitable stormwater collection system.
• Silt fences should be placed and maintained around the downslope sides of any
proposed excavations that will be exposed to the weather.
• Soils that are to be reused around the site should be stored in such a manner as to
reduce erosion from the stockpile. Suitable protective measures for the small amount
of excavated soil at the site would be covering the stockpiles with plastic sheeting.
• Areas stripped of natural vegetation during construction should be replanted as soon
as possible or otherwise protected.
6 PROJECT NO. 060266-002-01 • JANUARY 17; 2007 °°°~
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• Provisions of the Jefferson County Grading, Drainage, Erosion, and Sedimentation
Control standards should be used on the site.
2.3 Landslide Hazards and Mitigation.
Two types of landslides are common in the Puget Sound area, rotational landslides and
surficial or debris landslides. These slides may be triggered by natural events such as
extended, heavy precipitation or an earthquake, or by manmade features such as broken
water pipes or improperly managed storm water flow.
2.3.1 Rotational Type Landslides
Rotational landslides consist of deep-seated failures that typically involve slip along a
curved shear plane. Rotational landslides may transport large masses of semi-intact soil
downslope, resulting in alternating steep headscarps along .the upper portion of the failure
plane with more gently-sloping benches composed of displaced soil. We observed no
obvious evidence along the site slope or along the nearby slopes that suggested the
presence of recent, active or incipient static slope failure associated with deep-seated,
rotational landslides. The results of seismically induced sliding have been discussed in
Section 2.1.2.
2.3.2 surficial or Debris Landslides
Surficial or debris landslides consist of sliding of the weathered colluvial soil layer and
overlying vegetation that typically mantles steep slopes in the Puget Sound region.
Surficial slides commonly result from a significant increase in the moisture content
within the upper weathered soil layer on slopes. Increased moisture typically results from
periods of extended, heavy precipitation, groundwater seepage or concentrated surface
water discharge onto a slope. We', observed evidence of surficial slide activity that could
affect the proposed project. Slides of this type will occur in the future due to the
steepness of the slope and the presence of surficial weathered soil. Slides that occur
within the upper several feet of weathered soils typically do not extensively impact the
underlying, parent soils. Typically, catchment walls or foundations designed as retaining
walls are most effective at mitigating surficial landslide hazards, and are discussed in the
design recommendation section.
g.w PROJECT NO. 060266-002-01 • JANUARY 17, 2007 7
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3 Design Recommendations
3.1 Site Preparation
Those portions of the existing house or garage and foundations that are not part of the
proposed project should be removed. Any buried utilities that are to be abandoned should
be removed or relocated if they are under building areas. The resulting depressions
should be backfilled with structural fill, as discussed under Section 3.2, Structural Fill.
3.1.1 Clearing and Filling
Site preparation of planned building and driveway areas should include removal of all
trees, brush, debris, and any other deleterious material. Organic topsoil should be
removed and the remaining roots grubbed. Areas where loose surficial soils exist due to
grubbing operations should be considered as fill to the depth of disturbance and treated as
subsequently recommended for structural fill placement. The upper 12 inches of the soils
that will be exposed, as a result of stripping and grubbing should be recompacted to a
firm and non-yielding condition. This recompacted fill will serve primarily as a working
surface during construction.
3.1.2 Si#e Disturbance
The near-surface on-site soils contain areas with a high percentage offine-grained
material (silt) or organic matter, which makes them moisture-sensitive (subject to
disturbance when wet). The contractor must -use care during site preparation and
excavation operations so that the underlying soils are not softened. If disturbance occurs,
the softened soils should be removed and the area brought to grade with structural fill.
Consideration should be given to protecting access and staging areas with an appropriate
cover of crushed rock.
3.2 Structural Fill
Structural fill will be necessary to establish desired grades, particularly in areas where
unsuitable loose soils have been removed, such as in the vicinity of the proposed
catchment walUresdence construction. All references to structural fill in this report refer
to subgrade preparation, fill type, placement, and compaction of materials as discussed in
this section. Different percentages of compaction may be specified in other sections of
this report for other purposes. `~
After overexcavation/stripping have been completed; the upper 12 inches of exposed
ground should be recompacted to at least 90 percent of the Modified Proctor maximum
density using ASTM D 1557 as the standard. If the subgrade is within 2 feet of the final
foundation bearing grade, then it should be compacted to 95 percent of maximum or as
close as practical. If the subgrade contains too much moisture, adequate recompaction
may be difficult or impossible to obtain and should probably not be attempted. In lieu of
8 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 °"
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recompaction, the area to receive fill can be blanketed with compacted washed rock or
quarry spans to act as a capillary break between the new fill and the wet subgrade.
After recompaction of the exposed ground is tested and approved, or afree-draining rock
course is laid, structural fill may be placed to attain desired grades. Structural fill. is
defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum
12-inch-thick, loose, horizontal lifts with each lift being compacted to 95 percent of the
Modified Proctor maximum density using ASTM D-1557 as the standard.
The contractor should note that any proposed fill soils must be evaluated by Aspect
Consulting prior to their use in Ells. This would require that we have a sample of the
materia148 hours in advance to perform a Proctor test and determine its field compaction
standard. Soils in which the amount offine-grained material (smaller than No. 200 sieve)
-. is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should
_ be considered moisture-sensitive. Use ofmoisture-sensitive soil in structural fills should
be limited to favorable, dry weather conditions. The on-site sails contained variable
amounts of silt, and while considered moisture-sensitive, may be suitable for use as
structural fill, provided they can be demonstrated to compact and perform well. If fill is
placed during wet weather or if proper compaction cannot be obtained, a select import
material consisting offree-draining gravel and/or sand should be used. Free-draining fill
consists ofnon-organic soil with the amount offine-grained material limited to 5 percent
by weight when measured on the minus No. 4 sieve fraction.
3.3 Foundations
Bearing soils were encountered at a depth of approximately 1.5 feet in the vicinity of the
proposed house; consequently, shallow spread footings may be used for foundation
~-- support.
3.3.1 Spread Footings
Spread footings may be used ~for'support of the house when founded on the medium
dense to very dense, silty, sandy gravel encountered at approximately 1.5 feet below
existing site grade near the existing house. We recommend an allowable foundation soil
bearing pressure of 2,000 pounds per square foot (psf) be utilized for design purposes
including both dead and live loads. An increase in the above-mentioned bearing pressures
by one-third may be used for short-term wind or seismic loading. Perimeter footings
~ _ _ _ should be buried_a minimum of 1-8 inches into the surrounding soil for frost protection; __ __
however, all footings must penetrate to the prescribed bearing stratum at approximately
1.5 feet below the existing ground surface.
It should be noted that the area bounded by lines extending downward at 1H:1V from any
• footing must not intersect another footing, or a filled area that has not been compacted to
at least 95 percent maximum dry' density in accordance with ASTM test D-1557. In
~--- addition, a 2H:1 V line extending down from any footing must not daylight onto site
slopes. Thus, footings should not be placed near the edge of steps or cuts in the.. bearing
soils.
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PROJECT N0.060266-002-01 • JANUARY 17, 2007 9
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Anticipated total settlement of footings founded on properly prepared, medium dense to
very dense, silty, sandy gravel subgrade should be on the order of %i-inch. However,
disturbed soil not removed from footing excavations prior to footing placement could
result in increased settlements. All footing areas should be inspected by Aspect
Consulting, prior to placing concrete, to verify that the design bearing capacity of the
bearing soils has been attained and that construction conforms to the recommendations
contained in this report. Perimeter footing drains should be provided as discussed under
Section 3.6 of this report.
3.4 floor Support
Slab-on-grade floors may be used for the house, if placed over the undisturbed, silty,
sandy gravel bearing stratum or compacted structural fill bearing on that stratum. Slab-
on-grade floor areas should be excavated to a minimum of 4 inches below the bottom of
slab and then backfilled and compacted with a minimum of 4 inches of coarse drainage
aggregate material such as pea gravel or washed, crushed rock. This provides a pad of
structural fill as well as a capillary break between the ground surface and concrete slab
and provides proper drainage. Additionally, an impervious moisture barrier should be
placed directly below the slab.
3.5 Catchment Wall Recommendation
Based on the slope conditions at the site, construction of the southeast-facing portion
(facing the adjacent slope) of the proposed house foundation as a catchment wall will
provide protection against future landslide activity. This section of the report presents
preliminary design considerations and criteria that should be considered in the design of
the catchment wall.
3.5.1 Catchment Wall Criteria
subgrade preparation for the portion of foundation serving as the catchment wall
foundation should be performed in accordance with the recommendations presented in
the Section 3.2, Structural Fill.
In order to minimize the retaining wall height and required lateral design forces, and to ,,
comply with the Jefferson County critical areas setback criteria, we recommend
incorporating a minimum 15-foot-wide, flat area between the wall and the toe of the
existingslope,to act as a run-outJcatchmentarea. The run=out area will also facilitate the
removal of debris when necessary. Utilizing a 15-foot-wide run-out/catchment area, the
wall should extend a minimum of 10 feet above grade level in order to accommodate the
volume of material capable of being mobilized. The exposed portions of walls subject to ~.`~
impact loading should be designed to withstand a dynamic equivalent earth pressure of
90 pounds per cubic foot (pcf) to resist the impact area of the landslide, and a static
equivalent fluid pressure of 60 pcf over the full height of the wall. These two loads would
not occur simultaneously. Apassive resistive footing pressure of 350 pcf can be utilized J
if the concrete is poured "neat" against the native soil. If re-compacted fill is used for
resistance, a value of 250 pcf can be utilized. , ' '~
10 PROJECT NO. 060266-002-01 • JANUARY 17, 2007
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Any material which accumulates against the wall must be removed as soon as possible to
provide continuing protection for any subsequent event.
3.6 Drainage ConsideratNOns
All footings should be provided with a drain at the footing elevation. Drains should
consist of rigid, perforated, polyvinyl chloride (PVC) pipe sun-ounded by washed drain
gravel that is sized to avoid plugging or entering the drain pipe holes. The level of the
perforations in the pipe should be .set approximately 2 inches below the bottom of the
footing and the drains should be constructed with sufficient gradient to allow gravity
discharge away from the structure. Roof and surface runoff should NOT discharge into
the footing drain system but should be handled by a separate, rigid, tightline drain that
safely discharges to a natural drainway.
In planning, exterior grades adjacent to walls should be sloped away from the structure to
achieve surface drainage. Below-grade walls should be designed as retaining walls and
should be provided with a minimum 1-foot-thick, free-draining layer of drainage
aggregate along the entire height',of the wall to within 12 inches of final grade, in addition
to the footing drain system. All landscape walls over 3 feet high should incorporate a
1-foot-thick free-draining layer of drainage aggregate along the entire height of the wall.
Shallow diversion ditches should be placed on the upslope side of the walls to collect and
divert surface water and sediment so that it does not enter the wall drains.
3.7 Project Design and Construction Monitoring
At the time of this report, site grading, structural plans, and construction methods had not
been finalized. We are available T`o provide additional geotechnical consultation as the
project design develops and possibly changes from that upon which this report is based.
We recommend that Aspect Consulting perform a geotechnical review of the plans prior
to final design completion. In this way,. our earthwork and foundation recommendations
may be properly interpreted and implemented in the design.
We are also availableto provide geotechnical engineering and monitoring services during
construction. The integrity of the foundation and retaining wall depends on proper site
preparation and construction. procedures. In addition, engineering decisions may have to
be made in the field in the event that variations in subsurface conditions become
apparent. Construction monitoring services are not part of this current scope of work. If
these services are desired, please contact us aril we will prepare a cost proposal:
PROJECT N0.060266-002-01 • JANUARY 17, 2007 11
ASPECT CONSULTING
Limitations
Work for this project was performed and this report prepared in accordance with
generally accepted professional practices for the nature and conditions of work completed
in the same or similar localities, at the time the work was performed. It is intended for the
exclusive use of Tom Eastgard for specific application to the referenced property. This
report does not represent a legal opinion. No other warranty, expressed or implied,
is made.
,--
3
1
`I
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12 PROJECT NO. 060266-002-01 • JANUARY 17, 2007 ~~~°~
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Jan 2007
SieL nM
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AsectC®ns~€t~ng P ar oso2ss
JAP _
!N-DEPTH PERSPECTlVc' muveaer FIGURE NO.
t79Madm~uLaneNaM a„p~an„am,ax+eo Eastgard Residence PM6
eai,dN;aaa,~aw,wnssno s~amawnsa,oa aenamar
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E~B-1~ Approximate location of explorat~tion Plan
fence
Washington
~~
Not. to Scale
Jan 2007 PROJECT NO.
®'" 060266
JAP
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APPENDIXA
Boring Logs
a
•0 0 Well-graded gravel and Terms Describing Relative Density and Consistency
o
~, . ~.
g o Gyy gravel with sand, little to t2)
Dens SPT blows/foot
LL ~ •0.0
o no fines
Very Loose 0 to 4
Coarse-
>
m ~ ~
° - ~ o °o 0 0 o
o~ooo
Poorly-graded gravel Loose 4 to 10
Grained Solis Medium Dense 10 to 30
Test Symbols
° ° °
°
° GP tS Sand,
r 50 G =Grain Size
D
o
a o
o z oo
oa
o
o 0 0 0 o no fib
tt e fo ery Dense >50
M=Moisture Content
t2l
z ° o Silty gravel and silty blows/foot A = Atterberg Limits
Consistency SPT
~
- ° m
~ ~
v, GM gravel with sand ~ne_ Very Soft 0 to 2 C =Chemical
Soft 2 to 4 DD =Dry Density
°o,
C ~ ;~
O ~ iu
1LL ° Grained Soils Medium Stiff 4 to 8 K =Permeability
~ ~ ~
_m ~
Clayey gravel and Stiff 8 to 15
Very Stiff 15 to 30
"'
e > ~ GC clayey gravel with sand Hard >30
~
~ Component Definitions
s o Well-graded sand and Descriptive Term Size Range and Sieve Number
~ ~ sw sand with gravel, little Boulders Larger than 12"
°
~ ,~ ~ : to no fines Cobbles 3" to 12"
°' ~` :
:
~.
' "
~
~
a°
.
.
.
l
d
d
d to No. 4 (4.75 mm)
Gravel 3
m ~
° ~; ... san
Poor
y-gra
e Coarse Gravel 3" to 3/4"
U
~ gp and sand with gravel, Fine Gravel 3/4" to No. 4 (4.75 mm)
m
c F
o v
~, d little to no fines
Sand No. 4 (4.75 mrn) to No. 200 (0.075 mm)
~ ~ z
Silty Sand and Coarse Sand No. 4 (4.75 mm) to No: 10 (2.00 mm)
m ` ~
° :. :, . Medium Sand No. 10 (2.00 mm) to No. 40 (0.425 mm)
~ ~ - : • : SM silty sand with
Fine Sand No. 40 (0.425 mm) to No. 200 (0.075 mm)
U 0
c n.
~
•::
: '
gravel
Sift and Clay Smaller than No. 200 (0.075 mm)
'
y ~; ~
.
- Clayey sand and C3~
Estimated Percentage Moisture Content
~ ^~ sc clayey sand with gravel Percentage Dry -Absence of moisture,
by Weight Modifier dusty, dry to the touch
Silt, sandy silt, gravelly silt, <5 Trace Slightly Moist -Perceptible
m
m o
~ ML silt with sand or gravel moisture
5 to 15 Slightly (sandy, silty, Moist =Damp but no visible
~s~ clayey, gravelly) water
c°v .
U in
Clay of low to medium 15 to 30 San si ci Very Moist - Water visble but
dY, ftY, aYeY,
° mJ~ CL plasticity; silty, sandy, or gravely) not free draining
z
y .
E gravelly clay, lean Clay 30 to 49 Very (sandy, silty, Wet -Visible free water, usually
m ~ ~ clayey, gravelly) from below water table
a `~ ~ = Organic clay or silt of low S bols
c ~ _ OL Plasticity t3lows/6" or ~ ~~ scout
surface seal
~ _ Sampler portion of 6"
Bentonfte
YP8
~
il
i
El
i
il
l /
chips
l
T
S
lt
ast
t, c
ayey S
t,, s
c S amp
er
ype
2 0" OD ,~
o MH with micaceous or diato- Split-Spoon ~ Description Bentonite
l
~' ~ maceous fine sand or silt (SS ~Pler Continuous Push ~ sea
"
a
~
r°n °
v Clay of high plasticity 3.25
OD Spift-Spoon Ring Sampler <g :• s~bn
~
9
'°
m o
'° ~'
c c
CH ,
san or ravel) cla ,fat
~ g Y Y Bulk sample =
3.0" OD Thin-Wall Tube Sampler - Screened casing
`°. ~__ _ _ clay with sand or gravel _ , (including Shelbytube) - ._ or Hydrotip with
~ Grab Sample ., fitter pack
~ Q ~
/f
~ji Organic clay or silt of o Portion not recovered -- End cap
_
J ,
~
~~
~'' ~
i!
i~
f OH medium to high
(s)
t ~
i
i~
i~~,i~i~
plasticity Combined USCS symbols used for
Percentage by dry weight
t~
,i~,i (SPT) Standard Penetration Test fines between 5% and 15% as
'' °
c m Peat, muck and other (~~ D-1586) estimated in General Accordance
t3) In General Accordance with with Standard Practice for
~, W •o pT highly organic soils
Standard Practice for Description Description and Identificatior of
= o ~ and Identification of Soils (ASTM D-2488) Soils (ASTM D-2488)
(4)
Depth of groundwater ~ ATD = At time of drilling
~ Static water level (date)
Classifications of soils in this report are based on visual field and/or laboratory observations, which indude density/cons'tistency, moisture condition, grain s¢.e, and
plastidty estimates and should not be construed to impy field or laboratory testing unless presented herein. Visuahmanuaf and/or laboratory classification
methods of ASTM D-2487 and D-2488 were used as an identfication guide for the Unified Sal Classification System.
ASpeC~consulting
IN-OEP7N PERSPEC77VE
Exploration Log Key °"~°"°'°
O1"'""'" FIGURE NO.
tro waver ~.". cram ett FitYAw,nr aMeo
E"I
Wrd'WA 90/10
~
t
a
A"NIm•M
~~~
R08
~
7
N
.7
~
Aspect
~tl Borin Lo
COt15U
n
g Project Number ri
N
B
b Sh
t
IN-DEPTH PERSPECTIVE ng
o
um
er ee
060266 EB-1 1 of 3
Project Name Eastgard Residence Ground Surface Elev
Location 45 ft West of Bluff /Jefferson County, Washin ton
Driller/Method Davies Drilling / 8" O.D. Hollow-stem a er Depth to Water
Sampling Method 2" O.D. split-spoon sampler i Hammer Weight: 140 Ib /Hammer Drop: 30" Start/Finish Date 1/2/2007
Depth /
Elevation Borehole Completion
Sample
Tests
Blows/ N-value
Materia
l Description
~P
(feet) Type/ID 6„ 10 20 30 40 Type (ft)
9 '` '~ `` TOPSOIL AND GRASS
EB-1 7 ~ PRE-ERASER UNDIFFERENTIATED DEPOSITS
10
Medium dense
light brown
moist
slightly gravelly
\ ,
,
,
,
\ silty, fine to coarse SAND (SM)
\ D Very dense, light brown, moist, silty, sandy GRAVEL
\ (GM); horizontal bedding around gravels; gravels
~ predominantty basaltic
5 Backfill
d
ith \
e
w
30 U 5
bentonite chips EB-2
50-5" 50+
D
0
D
0
10 D
EB-3 50-6" 50+ Brown; sand fine to caarse; gravel fine to coarse 10
D
D
D
D
15
EB-4 37
" 50+ 15
50-5
D
1
I
I
0
- _
_ I
I
. ~ .
- . --------------------
Dense; brown; etoist; -silly, fine to cflarse-SAND,
I
I _
. trace gravel (SM)
20 I
6 ~ 20
EB-5 26 1
~ Driller reports silt, sand, scattered gravel 20-25'
I
I ~
:•
~ --------------------
Very dense, IigM brown/reddish-brown, moist,
I °: slightly silty, slightly gravelly, fine to coarse SAND
I (SW SM)
Sampler Type: PID - Photoionizafion Detector (Headspace Measurement) Logged by: JAP
® No Recovery 1
Static Water Level Approved by: JAP
® 2" OD Split Spoon Sampler
~ Water Level (ATD)
Figure No. 2
I
I
I
c
c
0
a
z
u
C
u
c
r~
r
-.
r
r
Aspect
ltt Borin Lo
g
Ct)fiStl
n Pro
ct N
b B
i
N
mb Sh
t
tN-DEPTH PERSPECTNE je
um
er or
ng
er
u ee
060266 EB-1 2 of 3
Project Name Eastgard Residence Ground Surface Elev
Location 45 ft West of Bluff /Jefferson County, Washi ton
Driller/Method Davies Dnllinq / 8" O.D. Hollow-stem auger Depth to Water
Sampling Method 2" O.D. split-spoon sampler /Hammer Weight:140 Ib /Hammer Drop: 30" StarUFinish Date 1/2/2007
Ele~waG~on Borehole Completion Sample Tests Blows/ N-value Material Description Dap
(feet) TypellD 6„ 10 20 30 40 Type tft)
EB-6 18
50-5" 50+
Very dense, Gght gray to reddish-brown, slightly
gravelly, silty, fine io coarse SAND (SM); thin,
horizontal laminations
30
40 ~ 30
EB-7 50.5" ~+ .
- Driller reports possible wet layer 33'-34'
- Very dense, browNreddish-brown, slightly silty,
- slightly gravelly, fine to coarse SAND (SW-SM); no
35
40 - structure or bedding 35
EB-8
50-6" 50+
Very dense, reddish-brown to gray, siKy, very sandy
GRAVEL (GM)
40
EB-9 50-5" ~' 40
0
- D
_ _ __
_ 0 _
45
EB-10 50-5" ~+ ~
0 45
i
i
i U
0
- Very dense, GgM gray, very moist, slightly silty,
. - slightly grave-ly, fine to coarse SAND (SW-SM)
Sampler Type: PID - Photoionizafion Detector (Headspace Measurement) Logged by: JAP
® No Recovery 1
Static Water Level
Approved by. JAP
® 2" OD Split Spoon Sampler
~
Water Level (ATD)
Fi ure No. 2
_. __ _~
c
c
0
c
a
u
c
u
c
n
A
t Borin Lo
eC
cansuttin
S
F` g Project Number Boring Number Sheet
IN-0EP7H PERSPECTNE
060266
EB-1
3 of 3
Project Name Eastgard Residence Ground Surface Elev
Location 45 fi West of Bluff /Jefferson County, Washington
Driller/Method Davies Drilling / 8" O.D. Hollow-stem auger Depth to Water
Sampling Method 2" O.D. split-spoon sampler /Hammer Weight: 140 Ib /Hammer Drop: 30" Start/Finish Date 1/2/2007
Depth /
Elevation
Borehole Completion
am
pl
e
S
Tests
81o
ws! N-value
MTt
e
neal
Description
~ ~
tf~t) p~
D
, G 10 20 30 4 Y
p
EB-11 50-5"
Driller reports cobbles 52'-53'
Very dense, gray, very moist to wet, sligMiy gravelly,
fine to coarse SAND, trace silt (SP); sand is
predominantly medium
55 55
31 ~. .:
EB-12 0-4.5
60 60
EB-13 23
50-5" 50+
Bottom of boring at 60.9 tt. Backfiiled with bentonite
chips.
65 65
70 70
Sampler Type: PID - Photoionization Detector (Headspace Measurement) Logged by: JAP
® No recovery 1 Static Water Level
® 2" OD Split Spoon Sampler 57 Approved by: JAP
Water Level (ATD)
Figure No. 2
s,-:>
~,
_!
c
c
c
~- c
J' a
z
u
c
u
c
~a
Aspect
l~l Borin Lo
g
COIiSU
ft Project Number Borin
Number Sh
t
!M-DEPTH PERSPECTNE g ee
060266 EB-2 1 of 1
Project Name Eastgard Residence Ground surface Elev
Location _50 ft West of B-1 /Jefferson County Washin ton
DNler/Method Davies Drilling / 8" O.D. Hollow-stem au er Depth to Water
Sampling Method 2" O.D. split-spoon sampler /Hammer Weight: 140 Ib /Hammer Drop: 30" Start/Finish Date 1/2/2007
Depth /
Elevation
Borehole Completion
Sample
Tests
Blows/ N-value
Materia
l Description
Dep
(reef) TypeJID G 20 30 40 5 Type (ft)
8 ` ' '` TOPSOIL AND GRASS
11
0 PRE-ERASER UNDIFFERENTIATED DEPOSITS
~
D Medium dense, reddish'-brown, moist, silly, sandy
_ ~ GRAVEL(GM)
~ ° Driller reports denser drilling at 2', coarse gravel at
~ D 3'
~ D
5 Backfilled
ith ~
w
bentonite chips
EB-2
50-5" ,p+ 0
Gravel fragments in sampler, brown, silty, gravelly 5
° sand in aattings
0
Driller reports cobbles 6'-10'
Very dense, light brown/gray, moist, silty, gravelly
• SAND (SM); homogeneous, no bedding
10
21 10
EB-3 50-5" sa+
15
EB-4
21
so+
Brown 15
50-3"
_ A Very dense,-taMight brown; moist. silty, sandy.. -
GRAVEL(GM)
D
20
i
EB-5
29
so+ D 20
0-3.5
i
Bottom of boring at 20.8 ft. Badfilled with bentonite
chips.
Sampler Type: PID - Photoionization Detector (Headspace Measurement) Logged by: JAP
®No Recovery 1
Static Water Level
Approved by: JAP
®2" OD Splft Spoon Sampler
Q
Water Level (ATD)
F' ure No. 3
r`':
~,
Ba'rnbridcte Island Location
-179 Madrone bane ~torth
Bainbridge Island, WA 98110
" Tel: (206) 780-9370
Fax: (206) 780-9438
Downtown Seattle Location
Colman Building ' "
811 First Avenue, Suite 480
Seattle, WA 98104
Tel: (206) 328-7443
Fax: (206) 838-5853