HomeMy WebLinkAboutGeotech Report, Soils Report, Addendum - GEO General - 7/31/2006 GEOTECHNICAL TESTING LABORATORY
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CONTACT INFORMATION
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PREPARER INFORMATION r
GTL PROJECT NUMBER: 06-2489-04
ADDRESS: 10011 BLOMBERG STREET SOUTHWEST
OLYMPIA,WASHINGTON 98512
-- � TELEPHONE: (360)754-4612
--• FACSIMILE: (360) 754-4848
EMAIL ADDRESS: GEOTESTLAB@COMCAST.NET
i CLIENT INFORMATION
CLIENT: D
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CELLULAR: (360)789-6514
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MAILING ADDRESS: 4326 LEGACY DRIVE
OLYMPIA,WA 98516
SITE ADDRESS: LOT 4
^-9991 EAST STATE ROUTE 106
UNION,WA 98592
PARCEL NUMBER: 322365100032
GPS LOCATION: N470 21.494' W1230 00.788'
10011 Blomberg Street SW, Olympia, WA 98512 2
Phone#: (360) 754-4612 Fax#: (360) 754-4848
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_ GEOTECHNICAL TESTtNO LABORATORY
SCOPE OF UNDERSTANDING
BOB DROHMAN
4326 LEGACY DRIVE
OLYMPIA,WA 98516
RE: GEOTECHNICAL REPORT
LOT 4
^-9991 EAST STATE ROUTE 106
UNION,WA 98592
PARCEL 322365100032
N470 21.494' W 1230 00.788'
-` As per your request, we have conducted a soils exploration, foundation evaluation, and slope stability analysis for
the above-mentioned parcel. The results of this investigation,together with our recommendations, are to be found
in the following report. We have provided three copies for your review and distribution.
Data has been carefully analyzed to determine soils bearing capacities, footing embedment depths, and setback
distances. The results of the exploration and analysis indicate that conventional spread and continuous wall
footings appear to be the most suitable type of foundation for the support of the proposed structure. Some
variability was encountered in comparing the soil profiles of the site. Net allowable soil pressures, embedment
depth, and total expected settlements have been presented for the site later in the report.
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Often, because of design and construction details that occur on a project, questions arise concerning soil
conditions. We would be pleased to continue our role as geotechnical consultants during the project
implementation. We appreciate this opportunity to be of service to you and we look forward to working with you
in the future. If you have any questions concerning the above items, the procedures used, or if we can be of any
further assistance please call us at the phone number listed below.
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Respectfully Submitted,
GEOTECHNICAL TESTING LABORATORY
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Harold Parks,L.G.,L.E.G.
En9lNe p 601001M Senior Engineering Geologist
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HAROLD PARKS
10011 Blomberg Street SW, Olympia, WA 98512 3
Phone#: (360) 754-4612 Fax#: (360) 754-4848
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GEOTECHNICAL TESTING LABORATORY
TABLE OF CONTENTS
CONTACTINFORMATION...................................................................................................................... 2
SCOPE OF UNDERSTANDING................................................................................................................ 3
TABLEOF CONTENTS............................................................................................................................. 4
INTRODUCTION........................................................................................................................................ 5
SITECONDITIONS.................................................................................................................................... 6
SurfaceConditions................................................................................................................................... 6
SiteGeology............................................................................................................................................. 7
SiteSoils................................................................................................................................................... 8
SubsurfaceExplorations........................................................................................................................... 8
Subsurface Conditions.........................................................................................................................: 8
SlopeStability .....................................................................................................................................:.... 8
CONCLUSIONS AND RECOMMENDATIONS..................................................................................... 10
General ................................................................................................................................................... 10
LANDSLIDE—EROSION HAZARD AREA........................................................................................... 10
Classification........ .............................................................................................................................. 10
SlopeStability ........................................................................................................................................ 11
BuildingSetback .................................................................................................................................... 12
Seismic—Liquefaction Hazard............................................................................................................... 14
ErosionControl ...................................................................................................................................... 15
EARTHWORK.......................................................................................................................................... 15
SitePreparation ...................................................................................................................................... 15
StructuralFill.......................................................................................................................................... 16
Suitability of Onsite Soils as Fill............................................................................................................ 16
Cutand Fill Slopes................................................................................................................................. 16
FoundationSupport................................................................................................................................ 17
FloorSlab Support.................................................................................................................................. 18
RetainingWalls...................................................................................................................................... 18
Slope Inclination: Equivalent Fluid Pressure......................................................................................... 18
RetainingWall Alternatives..........................................................................................:........................ 19
SiteDrainage.......................................................................................................................................... 19
Septic Impact. 19
LIMITATIONS .......................................................................................................................................... 20
FIGURE 1 VICINITY MAP....................................................................................................................... 21
10011 Blomberg Street SW, Olympia, WA 98512 4
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GEO"I'ECHNICAL TESTING LABORATORY
INTRODUCTION
This report summarizes the results of our geotechnical consulting services for the proposed single-family
residence to be located along the north-facing hillside, approximately 4 miles east of Union, Washington. The site
overlooks The Narrows along the southern shore of the Hood Canal. The location of the site is shown relative to
the surrounding area on the Vicinity Map, Figure 1.
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Otrr understanding of the project is based on our discussions with you and our explorations and review of the site.
We understand that the parcel is to be developed with a single-family residence. The site will be accessed by an
existing access road. In general, grading will consist of the excavation of the foundation and footings. The
approximate layout of the site is shown on the Site Plan, Figure 2.
The site predominantly slopes toward the north and west from the proposed building location. The steepest slope
measured onsite was in excess of 55 percent. Therefore, Mason County requires that a geotechnical report be
prepared in accordance with the Critical Areas Ordinance.
a 'The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for providing
potechnical recommendations and design criteria for the project and to satisfy the requirements of the Mason
aCamty Critical Areas Ordinance. Geotechnical Testing Laboratory is therefore providing geologic and
tiydrogeologic services for the project. Specifically, our scope of services for this project will include the
Mowing:
I. Review the available geologic,hydrogeologic, and geotechnical data for the site area.
2. Conduct a geologic reconnaissance of the site area and surrounding vicinity.
3. Investigate shallow subsurface conditions at the site by observing the exposed soil and reviewing
published well logs.
4. Evaluate the landslide and erosion hazards at the site per the Mason County Critical Areas Ordinance
regulations.
5. Provide geotechnical recommendations for site grading including site preparation, subgrade preparation,
fill placement criteria (including hillside grading), temporary and permanent cut and fill slopes, drainage,
and erosion control measures.
10011 Blomberg Street SW, Olympia, WA 98512 5
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C EOTECHNICAL 'TESTING LABORATORY
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SITE CONDITIONS
= SURFACE CONDITIONS
The proposed building site is located in an area of moderate residential development in the Puget Sound glacial
upland overlooking the Hood Canal. The site has a northern and western exposure. We conducted a
reconnaissance of the site area on April 19, 2006. Site elevations range from approximately 8 to 104 feet.
z The building area of the site has vegetation common to the Northwest. The vegetation includes fir, alder,
madrone, and cedar trees as well as huckleberry, salal, Oregon grape, bracken fern, sword fern, mullien,
blackberry, and grasses.
At the time of the site visit, active erosion was not observed at the proposed building location or throughout the
site. No evidence of deep-seated instability was observed at the proposed building location or throughout the site.
Surface water flow was not observed onsite. Seepage was not observed throughout the site. The general
topography of the site area indicates that drainage flows toward the west and north.
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10011 Blomberg Street SW, Olympia, WA 98512 6
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GEOTECHNICAiL, TESTING LABORATORY
SITE GEOLOGY
The site is generally situated within the Puget Sound glacial upland. The existing topography, as well as the
surficial and shallow subsurface soils in the area, are the result of the most recent Vashon stade (stage) of the
Fraser glaciation that occurred between about 9,000 and 11,000 years ago, and weathering and erosion that ha:
occurred since. A description of the surficial soils is included in the"Site Soils" section of this report. In general
the soils are composed of Vashon glacial material.
The Geologic Map of Washington — Northwest Quadrant (2002) has
mapped the site geology as advance outwash deposits (Qga) of
continental glacial origin. The report reads:
Advance outwash — Glaciofluvial sand and gravel and
lacustrine clay, silt, and sand deposited during the advance of
glaciers; sandy units commonly thick, well sorted, and fine
grained, with interlayered coarser sand, gravel, and cobbles;
locally contains nonglacial sediments and deposits mapped as
transitional between glacial and nonglacial. Includes the
Colvos and Esperance Sand Members of the Vashon Drift and
part of the Vashon Drift undivided.
The Geologic Map of Southeastern Mason County, Washington, USGS Water-Supply Bulletin 29 by Noble an(
Molenaar(1970)describes the site area as advance outwash. The advance outwash(Qva) is described as:
Gravel and sand, with some silt and clay at base. Unconsolidated and generally is in
discontinuous strata. Underlies till in most of area and up to 200 feet thick. Yields moderate to
large quantities (20-800 g.p.m.) of water where gravel and coarser sand facies below water
table.
The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan (2003) describes the site a
glacial advance outwash(Qga). The glacial advance outwash is described as:
Advance outwash, late Wisconsinan (Pleistocene)—Glaciofluvial sand and gravel and
lacustrine clay, silt, and sand deposited during the advance of glaciers; sandy units commonly
thick, well sorted, and fine grained, with interlayered coarser sand, gravel, and cobbles and silt
rip-up lag deposits at their base; may contain nonglacial sediments; generally overlain by till.
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10011 Blomberg Street SW, Olympia, WA 98512 7
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{ GE®TECHNICAL TESTING LABORATORY
SITE SOILS
The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as an
Alderwood gravelly sandy loam, 15 to 30 percent slopes(Ac). The survey reads:
This soil varies more in depth, but otherwise it is similar to Alderwood gravelly sandy loams, 5 to
15 percent slopes. It occurs in close association with and adjacent to that soil. It is on
moderately steep ridges, along drainageways, and on elongated irregular slopes. Small areas
with slopes of more than 30 percent are mapped with this soil. Surface drainage is more rapid
than on the more gentle slopes. Runoff and erosion on the logged and semicleared areas are
controlled by the dense growth of plants. Erosion would damage the soil if it were cleared for
crops.
SUBSURFACE EXPLORATIONS
Subsurface conditions at the site were evaluated by observing the exposed building site soil, reviewing available
well logs, and observing the site slopes. Part of the western slope is exposed due to previous grading. Static
groundwater was not encountered, presumed deep, and is beyond the scope of this report. Depth to competent soil
is approximately 8 inches throughout the proposed building location.
SUBSURFACE CONDITIONS
In general, undisturbed dense Alderwood gravelly sandy loam was observed in the undisturbed portions of the
site. At the proposed building location, glacial till was observed below the surficial soils. Based on the site
topography and the nature of the near-surface soil, seasonally perched groundwater conditions may be expected
during periods of extended wet weather.
SLOPE STABILITY
Slopes in excess of 55 percent were observed onsite. Since slopes of 40 percent or greater with 10 feet or more of
vertical relief occur on portions of the site, Mason County requires that a geologic hazards report be completed
according to the Critical Areas Ordinance.
The near-surface soils are in a dense to very dense condition except at the ground surface. The surficial soils are
generally in a medium dense condition.
10011 Blomberg Street SW, Olympia, WA 98512 8
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G-E®TECHNICA L TESTING LABORATORY
The Relative Slope Stability of the Southern Hood Canal
Area, Washington, (1977) describes the site area as Class 2.
Class 2 is described as: o0
Areas believed to be stable under normal conditions, µ,
but may become unstable if disturbed by man's
activities, if slope is oversteepened by erosion, or if Y
subjected to strong seismic shaking. Slopes a
- generally steeper than 15 percent, but may be less in u
some areas of weak geologic materials. Includes
areas underlain by: well-drained sand and gravel,
mostly on valley sides that lack known slope failures; S.
glacial till with steep slopes; and.bedrock. f r
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The Coastal Zone Atlas, Volume 9, Mason County (MA-9)
maps the site as Vashon Advance Outwash (Qva). The ,>
chance of flooding is less than one percent. Permeability is oa
described as high, while runoff potential is low. Infiltration
is moderate on natural slopes and high on cut slopes. S"i`'.�24'0°° Mk.
Springs at the bases of slopes are common (springs or seeps 6 "° '= I"° M.-
were not observed during the site reconnaissance). The slope
stability is described as"intermediate."
In general,the undisturbed native soils of the site consist of a mixture of variable amounts of sand, silt, and gravel.
These soil materials are in a dense condition except where they have been disturbed by weathering activity. These
soils are generally stable relative to deep-seated failure. Deep-seated landslide activity was not observed onsite at
the time of our investigation.
Weathering, erosion, and the resultant sloughing and shallow landsliding are natural processes that can affect
steep slope areas. Instability of this nature is typically confined to the upper weathered or disturbed zone, which
has been disturbed and has a lower strength. Raveling and sloughing were not observed onsite.
Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration,
wet/dry cycles, and freeze/thaw cycles. Erosion in steep slope areas such as this can be reduced by encouraging
vegetation and discouraging runoff from the steep slopes. Erosion control recommendations for the sloping areas
are provided in the"Erosion Control" section of this report.
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10011 Blomberg Street SW, Olympia, WA 98512 9
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GEOTECHNICAL TESUNO LABORATORY"
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CONCLUSIONS AND RECOMMENDATIONS
GENERAL
Based on the results of our site reconnaissance, subsurface observations, and our experience in the area, it is our
opinion that the site is suitable for the proposed project. The western slope will not be affected by the proposed
structure. The proposed structure will not undermine adjacent slopes. Proper drainage control measures will
reduce or eliminate the potential for erosion in this area and improve slope stability. The hazards of the landslide
area can be overcome in such a manner as to prevent harm to property and public health and safety, and the
project will cause no significant environmental impact for the life of the project.
In general, the Alderwood gravelly sandy loam soils observed at the site may be suitable for use as structural fill
material. Saturated soil conditions are not associated with these soils during or following extended periods of
rainfall. However, to reduce grading time and construction costs, we recommend that earthwork be undertaken
during favorable weather conditions.
Conventional construction equipment may be utilized for work at the site. Conventional spread footings may be
utilized at the site for support of the structure. We do recommend that roof and footing drains be installed for the
structure with conventional spread footings. A vapor barrier is recommended for all slabs-on-grade.
Pertinent conclusions and geotechnical recommendations regarding the design and construction of the proposed
single-family residence are presented below.
LANDSLIDE - EROSION HAZARD AREA
CLASSIFICATION
The Mason County Critical Areas Ordinance (17.01.100) defines a landslide hazard area as one containing slopes
equal to or greater than 40 percent with more than a 10-foot vertical relief. The western slope is in excess of 55
percent and the vertical relief is in excess of 10 feet. Based on the preceding, this site does meet the technical
criteria of a landslide hazard.
10011 Blomberg Street SW, Olympia, WA 98512 10
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GEOTECHNICAL TESTING LABORATORY
The Mason County Critical Areas Ordinance(17.01.104)defines an erosion hazard area as:
Areas in Mason County underlain by soils which are subject to severe erosion when
disturbed. Such soils include, but are not limited to, those for which potential for erosion
is identified in the Soil Survey of Mason County, USDA Soil Conservation Service, 1960,
or any subsequent revisions or additions to this source. These soils include, but are not
limited to, any occurrence of River Wash ("Ra') or Coastal Beaches ("Cg') and the
following when they occur on slopes 15%or steeper:
a.Alderwood gravelly sandy loam ("Ac"and"Ad')
b. Cloquallum silt loam ("Cd')
c. Harstine gravelly sandy loam ("Hb')
d. Kitsap silt loam ("Kc')
The soils at the site are mapped as Alderwood gravelly sandy loam(Ac). This site does meet the technical criteria
of an erosion hazard area.
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SLOPE STABILITY
Based on our field observations, explorations, and our experience with the soil types encountered on the property,
we conclude that although portions of the slopes on the lot exceed 55 percent, the proposed building location is
generally stable relative to deep-seated failure at the present configuration.
Excavation and backfilling will occur based on appropriate engineering and earthwork recommendations found in
the following"Earthwork" section. Grading in the building portion of the site should be conducted in accordance
with geotechnical recommendations provided herein.
As previously discussed, weathering, erosion, and the resultant surficial sloughing and landsliding are natural
processes that affect slope areas. Significant weathering typically occurs in the upper 2 to 3 feet and is the result
of oxidation, root penetration, wet/dry cycles and freeze/thaw cycles. Over-excavation may be necessary to
ensure the removal of deleterious material.
These processes can be managed and the risk reduced through proper construction of the residence. Erosion
control recommendations in the slope and buffer areas are provided in the "Building Setback" and "Erosion
Control" sections of this report.
10011 Blomberg Street SW, Olympia, WA 98512 11
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CE®TECHNICAL TESTING LABORATORY
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BUILDING SETBACK
A building setback from landslide hazard areas is required unless evaluated and reduced by an engineerin.
geologist or a licensed professional engineer. Based on our geotechnical evaluation of the site and our experienc
in the area, a building setback will be needed for this lot. The building setback may be measured from the bottor
of the footing to the face of the steep slope in accordance with the International Building Code (1805.3.1). Th
following figure represents a shear angle for the gravelly sandy loam. Shear angle and cohesion are variables use,
to model the site.
Peak Shear Stress vs. Normal Stress
3000
Shear= 38°
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2500
2000
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y 1500
d
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A
a
loon
T
f-1/4ton
500
—1/2 ton
—�-1 ton
Cohesion =
200 psf �'
0 500 1000 1500 2000 2500 3000
Normal Stress(psf)
Setback
10011 Blomberg Street SW, Olympia, WA 98512 E
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GEOTECKNICA L TESTING LABORATORY
Slope stability was modeled using the GeoStudio 2004 (version 6.17) in both static and extreme dynan
conditions (Ca = 0.3). Factors of safety were determined using Bishop's, Janbu, and the Morgenstern-Pr.
methods. The site was modeled using a monolithic layer of gravelly sandy loam. The gravelly sandy lo,
material was determined to have a unit weight of 122 pcf, cohesion of 200 psf, and a shear angle (�) of I
Under static conditions, the slope was not susceptible to shallow failure or susceptible to deep-seated failu
Under dynamic loading,the 3,328 computations demonstrated that the slope is not susceptible to surficial raveli
or large deep-seated failure. The following figure illustrates the moment factor of safety for slope "A" under t
existing conditions. The figure is the solution of greatest concern and exhibits the need for a building setback
20 feet from the face of the western slope. All foundation elements shall be constructed on native material
engineered fill material.
Drohman Site -- Lot 4 • • • • • • •
80
70
60
50
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40 Description: Gravelly Sandy Loam
30 Wt: 122
w 20 Cohesion: 200
10 Phi: 38
0
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 24
Distance (ft)
10011 Blomberg Street SW, Olympia, WA 98512
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CEOTECHNICAL TESTING LABORATORY
As previously discussed, weathering, erosion, and the resultant surficial sloughing and shallow landsliding ar
natural processes that affect slope areas. Surficial raveling and sloughing were not observed onsite. To manag
and reduce the potential for these natural processes, we recommend the following:
➢ No drainage of concentrated surface water or significant sheet flow onto the sloped areas.
➢ No filling within the setback zone unless retained by retaining walls or constructed as an engineered fill.
SEISMIC—LIQUEFACTION HAZARD
According to the Seismic Zone Map of the United States contained in the 2003 International Building Code(IBC;
the project site is located where the maximum spectral response acceleration is 45 percent of gravity(g).
The Liquefaction Susceptibility Map of Mason County, Washington by Palmer, Magsino, Poelstra, Bilderback
Folger, and Niggemann (September 2004) maps the building site area as having a very low to low liquefactioi
potential.
` The Site Class Ma o Mason County, Washington b Ma sino Bilderback Poelstra Fol er an(
P .f tY� g Y Palmer, g � g ,
Niggemann (September 2004) maps the building site area as site class C to D. Site class C is a very stiff soil o
soft rock and site class D is a stiff soil.
Based on the subsurface conditions observed at the site, we interpret the site conditions to correspond to a seismic
Soil Profile Type D, for Stiff Soil, as defined by Table 1615.1.1 (IBC). This is based on probing with a '/z-incl
diameter steel probe rod. The shallow soil conditions were assumed to be representative for the site condition!
beyond the depths explored.
Based on our review of the subsurface conditions, we conclude that the site soils are only mildly susceptible tc
liquefaction. The near-surface soils are generally in a dense condition and the static water table is located wel
below the surface. Shaking of the already dense soil is not apt to produce a denser configuration and subsequentl3
excess pore water pressures are not likely to be produced.
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10011 Blomberg Street SW, Olympia, WA 98512 14
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G-EOTECHNICAL TESTING LABORATORY
EROSION CONTROL
It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed development.
Removal of vegetation should be minimized on the slopes. Hazard trees located on steep slopes may be removed
only if the stumps remain to deter erosion.
Temporary and permanent erosion control measures should be implemented and maintained during construction
and/or as soon as practical thereafter to limit the additional influx of water to exposed areas and protect potential
receiving waters.
Erosion control measures should include, but not be limited to, silt fences, berms, and swales with ground
cover/protection in exposed areas. A typical silt fence detail is included on Figure 2. Any re-contouring of the
site will create a need for erosion control measures as listed above.
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EARTHWORK
SITE PREPARATION
All areas to be excavated should be cleared of deleterious matter including any existing structures, debris, duff,
and vegetation. Based on our observations, we estimate that stripping on the order of 6 to 12 inches will be
necessary to remove the root zone and surficial soils containing organics. Areas with deeper, unsuitable organics
should be expected in the vicinity of depressions or heavy vegetation. Stripping depths of up to 2 feet may occur
in these areas. These materials may be stockpiled and later used for erosion control and landscaping. Materials
that cannot be used for landscaping or erosion control should be removed from the project site.
Where placement of fill material is required, the exposed subgrade areas should be proof-rolled to a firm and
unyielding surface prior to placement of any fill. We recommend that trees be removed with the roots, unless
located on a slope. Excavations for tree stump removal in any building area should be backfilled with structural
fill, compacted to the density requirements described in the"Structural Fill" section of this report.
If structural fill is needed, we recommend that a member of our staff evaluate the exposed subgrade conditions
after vegetation removal and topsoil stripping are completed. Any soft, loose or otherwise unsuitable areas
delineated during foundation preparation or probing should be compacted, if practical, or over-excavated and
replaced with structural fill,based on the recommendations of our report.
10011 Blomberg Street SW, Olympia, WA 98512 15
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GEOTECHNICAL TESTING LABORATORY
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STRUCTURAL FILL
All fill material should be placed as structural fill. The structural fill should be placed in horizontal lifts of
appropriate thickness to allow adequate and uniform compaction of each lift. Fill should be compacted to at least
90 percent of MDD (maximum dry density as determined in accordance with ASTM D-1557) to within 2 feet of
subgrade and 95 percent MDD in the upper 2 feet.
The appropriate lift thickness will depend on the fill characteristics and compaction equipment used. We
recommend that the appropriate lift thickness be evaluated by our field representative during construction.
The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil.
As the amount of fines (material passing No. 200 sieve) increases, soil becomes increasingly sensitive to small
changes in moisture content and adequate compaction becomes more difficult to achieve. During wet weather, we
recommend the use of well-graded sand and gravel with less than 9 percent(by weight) passing the No. 200 sieve
based on that fraction passing the 3/4-inch sieve.
If prolonged dry weather prevails during the earthwork and foundation installation phase of construction, a
somewhat higher(up to 10 percent)fines content will be acceptable.
Material placed for structural fill should be free of debris, organic matter, trash, and cobbles greater than 6 inches
in diameter. The moisture content of the fill material should be adjusted as necessary for proper compaction.
SUITABILITY OF ONSITE SOILS AS FILL
Onsite soils may be.considered for use as structural fill. In general, the native soils (sand, loam, and gravel)
encountered on the site must have less than 10 percent fines (material passing the US No. 200 Sieve) to be
suitable for use as structural fill.
CUT AND FILL SLOPES
All job site safety issues and precautions are the responsibility of the contractor providing services and/or work.
The following cut/fill slope guidelines are provided for planning purposes.
Temporary cut slopes will likely be necessary during grading operations.
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As a general guide, temporary slopes of 1.5 to 1 (horizontal to vertical) or flatter may be used for temporary cut
in the upper 3 to 4 feet of the glacially consolidated soils that are weathered to a loose/medium-dense condition
Temporary slopes of 1 to 1 or flatter may be used in the unweathered dense to very dense sands and gravel.
'- These guidelines assume that all surface loads are kept at a minimum distance of at least one-half the depth of th
cut away from the top of the slope and that significant seepage is not present on the slope face. Flatter cut slope
will be necessary where significant raveling or seepage occurs.
Surface drainage should be directed away from all slope faces. All slopes should be seeded as soon as practical t(
facilitate the development of a protective vegetative cover or otherwise protected.
FOUNDATION SUPPORT
Where foundation elements are located near slopes between 5 and 30 percent, the footings should be located
minimum of 2 times the footing width from the slope face (horizontally), and founded in medium dense or dense
native soils or properly prepared structural fill.
We recommend a minimum width for isolated and continuous wall footings to meet IBC 2003. Footings founder
as described above can be designed using an allowable soil bearing capacity of 2,000 psf(pounds per square foot
for combined dead and long-term live loads in areas of medium dense to dense soils.
The weight of the footing and, any overlying backfill may be neglected. The allowable bearing value may N
increased by one-third for transient loads such as those induced by seismic events or wind loads.
Lateral loads may be resisted by friction on the bases of footings and floor slabs and as passive pressure on the
sides of footings. We recommend that an allowable coefficient of friction of 0.40 be used to calculate frictior
between the concrete and the underlying soil. Active pressure may be determined using an allowable equivalen
fluid density of 150 pcf(pounds per cubic foot).
We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch, foi
the anticipated load conditions, with differential settlements between comparably loaded footings of '/z inch of
less.
Most of the settlements should occur, essentially as loads are being applied. However, disturbance of the
foundation subgrade during construction could result in larger settlements than predicted.
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10011 Blomberg Street SW, Olympia, WA 98512 17
Phone#: (360) 754-4612 Fax#: (360) 754-4848
G-E®TECHNICAL, TESTING LABORATORY
FLOOR SLAB SUPPORT
Slabs-on-grade should be supported on medium dense or dense native soils or on structural fill prepared
described in the "Structural Fill" section of this report. We recommend that floor slabs be directly underlain by
minimum 6-inch thickness of coarse sand and/or gravel containing less than 5 percent fines (by weight). Tl
drainage material should be placed and compacted to an unyielding condition.
A synthetic vapor barrier may be used for the control of moisture migration through the slab, particularly whe
adhesives are used to anchor carpet or tile to the slab. A thin layer of sand may be placed over the vapor barri
and immediately below the slab to protect the liner during steel and/or concrete placement. The lack of a vap,
barrier could result in wet spots on the slab,particularly in storage areas.
RETAINING WALLS
Retaining walls may be utilized on the sloping portion of the site to retain fill material. The lateral pressure
acting on the subgrade and retaining walls will depend upon the nature and density of the soil behind the wall.
is also dependent upon the presence or absence of hydrostatic pressure. If the adjacent exterior wall space
backfilled with clean granular, well-drained soil (washed rock), the design active pressure may be determine
using an active pressure coefficient equal to 0.25 (Ka = 0.25). This design value assumes a level backslope at
drained conditions as described below.
Retaining walls located on or near the toe of a slope that extends up behind the wall should be designed for
lateral pressure, which includes the surcharge effects of the steep slope in proximity to the wall. Although n,
expected at this site,the following data is provided for planning purposes.
For an irregular or composite slope, the equivalent slope angle may be determined by extending a line upwai
from the toe of the wall at an angle of 1 to 1 (Horizontal to Vertical)to a point where the line intersects the grour
surface. The surcharge effects may be modeled by increasing the equivalent fluid pressure for flat ground by tl
t percentage given in the following table:
SLOPE INCLINATION: EQUIVALENT FLUID PRESSURE
Slope Angle Percent Increase Equivalent Fluid Pressure
Horizontal 0% 35 pcf
3H:1V 25% 44 pcf
2H:1 V 50% 53 pcf
1H:1V 75% 61 pcf
If the walls are greater than 4 feet in height, exclusive of the footing, additional design considerations should t
applied.
Positive drainage, which controls the development of hydrostatic pressure, can be accomplished by placing a zor
of coarse sand and gravel behind the walls. The granular drainage material should contain less than 5 percei
fines. The drainage zone should extend horizontally at least 18 inches from the back of the wall. The drainaE
zone should also extend from the base of the wall to within 1 foot of the top of the wall. The drainage zor
should be compacted to approximately 90 percent of the MDD. Over-compaction should be avoided as this ca
lead to excessive lateral pressures.
A perforated PVC pipe with a minimum diameter of 4 inches should be placed in the drainage zone along the bay
of the wall to direct accumulated water to an appropriate discharge location.
a 10011 Blomberg Street SW, Olympia, WA 98512 1
Phone#: (360) 754-4612 Fax#: (360) 754-4848
C EOTECHNICAL TESTING LABORATORY
We recommend that a non-woven geotextile filter fabric be placed between the drainage material and the
remaining wall backfill to reduce silt migration into the drainage zone. The infiltration of silt into the drainage
zone,with time, can reduce the permeability of the granular material.
The filter fabric should be placed in such a way that it fully separates the drainage material and the backfill, and
should be extended over the top of the drainage zone.
Lateral loads may be resisted by friction on the bases of footings and as passive pressure on the sides of footings
and the buried portions of the wall. We recommend that an allowable coefficient of friction of 0.40 be used to
calculate friction between the concrete and the underlying soil.
RETAINING WALL ALTERNATIVES
Typically, block wall systems are more cost effective for long-term walls than the other options. Specific design
criteria for these options can be provided at your request by the block manufacturers.
SITE DRAINAGE
All ground surfaces, pavements, and sidewalks should be sloped away from the residence and associated
structures. Surface water runoff should be controlled by a system of curbs, berms, drainage swales, and/or catch
basins and tight-lined to the appropriate drainage facilities or to the base of the western slope. We recommend
that conventional roof drains be installed. Footing drains shall be installed for the single-family residence. The
roof drain should not be connected to the footing drain. For footing drains, the drain invert should be below the
bottom of the footing.
We recommend that the collected stormwater runoff be directed to the appropriate drainage facilities by tight-line
or to the base of the western slope. Drainage control measures are included on Figure 3. Onsite irrigation to lawn
areas should be closely monitored. We do not expect any adverse affects on the recharge condition of the
groundwater system.
SEPTIC IMPACT
The location of the proposed septic drainfield will be offsite to the southeast. Since the location is in an area
where the slope is approximately 15 percent,the slope stability will not be compromised.
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10011 Blomberg Street SW, Olympia, WA 98512 19
Phone#: (360) 754-4612 Fax#: (360) 754-4848
CEOTECHNICAhL TESTING LABORATORY
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LIMITATIONS
We have prepared this report for Bob Drohman and members of his design team to use in the design
of a portion
of this project. The data used in preparing this report, and this report, should be provided to prospective
contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on
data from others and our site reconnaissance, and should not be construed as a warranty of the subsurface
conditions. This report is quantified as a micro-study and not a macro-study. Geotechnical Testing Laborato
and its personnel cannot be responsible for unforeseen and widespread geologic events (such as earth u rY
large-scale faulting, and mass wasting) beyond the scope of this project. q akes,
Variations in subsurface conditions are possible and may occur with time. A contingency for unanticipated
conditions should be included in he budget and schedule. Sufficient consultation should be made with our firm
during construction to confirm that the conditions encountered are consistent with those indicated by the
recommendations and for design changes should the conditions revealed during the work differ from hose
anticipated, and to evaluate whether earthwork and foundation installation activities comply with contract plans.
If our analysis and recommendations are followed, we do not anticipate any on site or off site impact from the
construction. It is our conclusion that potential landslide hazards from the landslide area can be overcome so as
not to cause harm to property,public health and safety, or the environment.
The scope of our services does not include services related to environmental remediation and construction safety
precautions. Our recommendations are not intended to direct the contractor's methods, techniques, sequences or
procedures, except as specifically described in our report for consideration in design.
If there are any changes in the loads, grades, locations, configurations or types of facilities to be constructed, the
conclusions and recommendations presented in this report may not be fully applicable. If such changes are made,
we should be given the opportunity to review our recommendations and provide written modifications or
verifications, as appropriate.
10011 Blomberg Street SW, Olympia, WA 98512
Phone#: (360) 754-4612 Fax#: (360) 754-4848 20
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1 I 1 1 1 6 NSECURELY/�'MU 6-INCH OVERLAP D Y AT
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OF POSTS AND UPSLOPE FROM THE BARRIER.
Olympia,WA 98512
.ILTER FABRIC 13 USED,A WIRE MESH
TENED SECURELY TO THE UPSLOPE SIDE Phone:(360)754-4612
2 VA n �UTY RE STAPLES AT LEAST 1 INCH
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GROUND SURFACE.
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OF FABRIC SHALL BE EXTENDED
SHALL NOT EXTEND MORE THAN 36 Designed by: LL
GROUND SURFACE.FILTER FABRIC SHALL
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A FABRIC AND CLOSER POST SPACING IS Checked by: LL
FIT FENCE MAP BE ELIMINATED,IN SUCH
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NOT BE REMOVED BEFORE THE UPSLOPE
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BE INSPECTED IMMEDIATELY AFTER EACH
DURING PROLONGED RAINFALL.ANY
MADE IMMEDIATELY.
res:
I SHALL BE IN PLACE PRIOR TO THE
1.THE PROJECT ENGINEER AND THE COUNTY
THE INSTALLATION OF
5 PRIOR TO BEGINNING CONSTRUCTION.
ARE NOT LIMITED TO THE ITEMS
ORISRELL NSIBEROSION
CONTROR OL
PROJECT NAME:
ACE OF ALL EROSION CONTROL MEASURES.
PROPOSEDTAKEN TO
PREVFAC ENT
DROHMAN SITE
ILL BE TAKEN TO PREVENT MIGRATION
IES.
DAILY SURVEILLANCE OF ALL EROSION LOT 4
E ANY NECESSARY REPAIRS OR AOOTIONS -9991 EAST STATE ROUTE
1SURE8.THE CONTRACTOR SHALL PROVIDE
: EASURES ASIORTHEPROJ CTENGINEO.FAILURE UNION,WASHINGTON
41)STA HE PROTON CONTROL
N .FAILURE
IDVIL PENALTIES
BEI0L PARCEL 322365100030
I CIVIL PENALTIES BEING LEVIED
D/OR PROJECT OWNER.
TMSER TO MARCH)ALL DISTURBED SOILS
I HOURS AFTER STOP OF WORK EROSION Re1�si0rls:
:LODE,BUT NOT BE LIMITED TO,
\INCLUDING SPOIL PILES WTTH
TTING,JUTE MATTING,STRAW MULCH,
THE DISTURBED AREAS SHALL TAKE
5 SHALL BE CHECKED REGULARLY
VERAGE IS COMLETE.AREAS SHALL BE
ITILIZED AS REQUIRED.
NORTH L NOT BE ALLOWED.IF ANY SOIL IS
SCALE 1°=517 EET,IT SMALL BE REMOVED BY THE END
URTHER TRACKING OF MUD WALL THEN
C.I.=2' )R WASHING OF THE VEHICLES TIRES
STREET.
DATUM ASSUMED CH ON A DOWNSLOPE OF MORE THAN 5
THIS IS NOT ASURVEY 'ONETIME.
E PLACED ON THE UPHILL SIDE OF TRENCHES.
0 10 20 30 40 50 SHALL SE DISCHARGED INA MANNER TKAT WILL
INO STREAMS.DRAINAGE SYSTEMS OR
SME:1 Inch=50 feet
0VING RUNOFF FROM THE PROJECT DURING
iTECTED SO THAT SEDIMENTIADEN WATER
1 'ERBIG THE CONVEYANCE SYSTEM.
I MEADIA N LY ADJACENT TO THE SITE
ILT3E SEEDED OR SODDED UPON COMPLETION FIGURE 2
HALL BE RESPONSIBLE TO ENSURE THAT
DISTURBED AREAS IS PROVIDED&THAT
IS ESTABLISHED. SITE PLAN
)BAENT OR FILTER FABRIC MUST BE
EGETATION IS ESTABLISHED.
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3 FOOT REBAR LENGTHS OR BOLTS.
FLARE END SECTION
QUARRY SPALL a 'ice
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GRASS-LINED SWALE SHOULD BE A
MINIMUM ONE FOOT WIDE AT THE
BOTTOM AND ONE FOOT DEEP WITH
A MAXIMUM SLOPE OF 5 PERCENT.
MINIMUM 4 FEET
LEVEL SECTION
GEOTEXTILE FABRIC
Geotechnical Testing Laboratory
Geooed nical Services 10011 wAriiDeraeasst.sw FIGURE 3
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Services Fax(360)7544M Not to scale DRAINAGE DETAILS