HomeMy WebLinkAboutGeo-Report Review for BLD2005-00546 - BLD Engineering / Geo-tech Reports - 4/12/2005 ° .STArF°�
M C MASON COUNTY
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o S U PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER
N Shelton,Wuhington 98584
r2�OJ N Y Gov DATE: April 121h, 2005
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INTER-DEPARTMENTAL COMMUNICATIONS
TO: Kell McAboy, DCD—Planner
FROM: Alan A. Tahja, P/W - Co. Hydr. Engr. WO# PLG-05
SUBJ: Geo-Report Review NAME: Selleg SFR g 1050 Jensen Road
BLD2005-00546
Kell,
The geotechnical report prepared for the proposed Bruce Selleg Single Family Residence (SFR)
to be constructed at 1050 E. Jensen Road, Shelton, has been received and reviewed by Public
Works.
The report appears to satisfactorily address County requirements for geotechnical reporting. The
report's author indicates that, in his opinion, the proposed development of the property will not
cause stability problems for either the subject property or neighboring properties. From the
contents of the report, I recommend accepting the report as satisfying the County's
requirement(s) for stability investigation and geotechnical reporting. The 20 foot building setback
from the crest of the southwesterly slope recommended in the report should be incorporated into
the site's development plans and made conditions for permit issuance. Other recommendations
and conclusions contained in the report should also be made conditions for project approval.
Erosion and sediment control measures recommended in the report should be made conditions
for permit issuance. The migration or release of silty water or mud from the applicant's property
will be considered a violation of County and State water quality protection regulations.
In summary, the geotechnical report appears acceptable, and the development of the lot for
residential development should be allowed to proceed, subject to the engineer's
recommendations.
Please feel free to contact me at County extension 461 if you have any questions regarding these
comments, or if you feel any features need further discussion or attention.
Sincerely,
AZ n A. Tahja
File: H:\WP\GEO\Reviews\Selleg.doc
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Geotechnical Report
1050 East Jensen Road
Shelton, WA
i
Prepared for
Bruce Selleg
by
Geotechnical Testing Laboratory
Olympia, Washington
February 1, 2005
GEOTECHNICAL TESTING LABORATORY
BRUCE SELLEG
1330 MAY AVENUE
SHELTON,WA 98584
RE: GEOTECHMCAL REPORT
1050 EAST JENSEN ROAD
SHELTON,WA 98584
PARCEL 321322200010
N47016.244' W123005.764'
INTRODUCTION
This report summarizes the results of our geotechnical consulting services for the proposed single-family residence
and future garage/shop to be located at 1050 East Jensen Road 3.0 miles northeast of Shelton, Washington. The
location of the 9.27-acre site is shown relative to the surrounding area on the Vicinity Map, Figure 1.
Our 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 as a single-family residence. The site will be accessed by a
driveway from East Jensen Road. In general,grading will consist of the excavation of the foundation and footings.
'Aff. - _ -Al Al a View Looking Southwest
The site predominantly slopes toward the west (Johns Creek) from the proposed building location. The steepest
slope measured onsite was in excess of 100 percent. Therefore, Mason County requires that a geotechnical report
be prepared in accordance with the Critical Areas Ordinance.
The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for providing
geotechnical recommendations and design criteria for the project and to satisfy the requirements of the Mason
County Critical Areas Ordinance. Geotechnical Testing Laboratory is therefore providing geologic and
hydrogeologic services for the project. Specifically, our scope of services for this project will include the following:
1. 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.
10011 Blomberg Street SW, Olympia,WA 98512 1
Phone#: (360) 7544612 Fax#: (360)7544848
GEOTECHNICAL TESTING LABORATORY
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.
SITE CONDITIONS
SURFACE CONDITIONS
The proposed building site is located in an area of sparse residential development in the Puget Sound glacial upland
area located east of Johns Creek. The proposed layout of the site is shown on the Site Plan, Figure 2. We
conducted a reconnaissance of the site area on January 14, 2005. Site elevations range from approximately 220 to
320 feet. Elevations in the building area are roughly 2 feet
in relief.
The proposed building location has vegetation common to
the Northwest. The vegetation includes fir, pine, and
maple trees as well as bracken ferns, sword ferns,
huckleberry, Scot's broom, salal, Oregon grape and
grasses.
At the time of the site visit, we observed no evidence of
surface erosion onsite. No evidence of deep-seated slope
a.
instability was observed. Minor sloughing or raveling was
observed onsite along Jensen Road.
Surface water flow was not observed onsite at the time of
our reconnaissance. The general topography of the site t
area indicates that drainage flows toward the west and
ultimately to Johns Creek.
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 10,000 and 12,000 years ago, and weathering and erosion that has 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 till material.
SITE SOILS
The Soil Survey of Mason County, USDA Soil Conservation Service (1960)has mapped the site soils as Alderwood
gravelly sandy loam, 5-15 percent slopes (Ab). The Alderwood soils typically formed from glacial advance
outwash. They are described as having good natural drainage. Typically, there is no occurrence of a high water
table. Internal drainage is described as medium. An erosion hazard may exist if the vegetation is removed;
otherwise, the soil has a low erosion hazard in its present condition. Cementation is usually present. The soils are
not considered hydric.
10011 Blomberg Street SW, Olympia,WA 98512 2
Phone 4: (360) 754-4612 Fax#: (360) 754-4848
GEOTECHNICAL TESTING LABORATORY
The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan (2003) describes the site as late
Wisconsinan(Pleistocene)glacial deposits. The glacial till(Qgt)is described as:
Unsorted, unstratified, highly compacted mixture of clay, silt, sand, gravel, and boulders
deposited by glacial ice of the Puget lobe; gray; may contain interbedded stratified sand, silt,
and gravel; sand-size fraction is very angular and contains abundant polycrystalline quartz,
which distinguishes this unit from alpine till; cobbles and boulders are commonly striated and
(or)faceted; although unweathered almost everywhere, may contain cobbles or small boulders of
deeply weathered granitic rock.
The Geologic Map of Washington—Northwest Quadrant(2002)has mapped the site geology as glacial till deposits
(Qgt)of continental glacial origin. The report reads:
fill— Unsorted, unstratified, highly compacted mixture of clay, silt, sand, gravel, and boulders
deposited by glacial ice; may contain interbedded stratified sand, silt, and gravel. Includes part
of the Vashon Drift undivided
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SUBSURFACE EXPLORATIONS
Subsurface conditions at the site were evaluated by observing the exposed building site soil and reviewing available
well logs. Groundwater is presumed deep due to the topography. Depth to competent soil is approximately 8 inches
throughout the proposed building site.
SUBSURFACE CONDITIONS
In general, undisturbed dense Alderwood gravelly sandy loam was observed throughout the site. Groundwater was
not observed or encountered. No instances of groundwater seeps were observed on the slopes or adjacent to the
10011 Blomberg Street SW, Olympia,WA 98512 3
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GEOTECHNICAL TESTING LABORATORY
parcel. Based on the site topography and the nature of the near surface soil, seasonally perched groundwater
conditions are not expected during periods of extended wet weather.
t 44 fr
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ar View Looking Northwest -
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SLOPE STABILITY
Slopes in excess of 100 percent were observed on the adjacent slope. 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 Relative Slope Stability of the Southern Hood Canal Area, Washington, (1977)describes the site area as Class
1. Class 1 is expressed as:
Areas believed to be stable. Slopes generally less than 15 percent, but may be greater locally in
areas too small to be shown at the map scale. Largely comprises rolling uplands underlain by
very stable material such as young glacial till, mantled in places by a thin layer of sandy gravel
or other permeable material; also includes flood plains, deltas, alluvial fans, and some beach
deposits. Class I areas immediately adjacent to steep slopes of class 3 areas may be threatened
by potential landsliding. Normal, proper engineering practices generally are adequate to
insure stability in these areas.
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.
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. No evidence of deep-seated landslide activity or significant
erosion was observed at the site 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. Evidence of minor raveling and sloughing was observed along the Jensen Road
easement southwest of the proposed building location where the road was cut into the bank.
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
10011 Blomberg Street SW, Olympia,WA 98512 4
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GEOTECHNICAL TESTING LABORATORY
vegetation and discouraging runoff from the steep slope. Erosion control recommendations for the sloping areas are
provided in the"Erosion Control"section of this report.
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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 slope is stable relative to deep-seated instability and
will not be affected by the proposed structures. The proposed structure will not undermine adjacent structures.
Proper drainage control measures will reduce or eliminate the potential for erosion in this area and improve slope
stability.
Based on the results of our site reconnaissance and subsurface observations, and our experience in the area, it is our
opinion that the site is suitable for the proposed single-family residence. 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.
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y
10011 Blomberg Street SW, Olympia,WA 98512 5
Phone#: (360) 754-4612 Fax#: (360) 754-4848
GEOTECHNICAL TESTING LABORATORY
In general, the Alderwood soils observed at the site are not 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 slab-on-grades.
Pertinent conclusions and geotechnical recommendations regarding the design and construction of the proposed
single-family residence are presented below.
LANDSLIDE—EROSION HAZARD AREAS
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 southwestern slope is in excess of
100 percent and the vertical relief is in excess of 10 feet. Based on this,this site does meet the technical criteria of a
landslide hazard.
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
1 S%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 (Ab). This site does not meet the technical
criteria of an erosion hazard area.
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 site exceed 100 percent, they are generally stable relative to
deep-seated failure in their present configuration.
Excavation and back-filling 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
10011 Blomberg Street SW, Olympia,WA 98512 6
Phone#: (360) 754-4612 Fax#: (360) 754-4848
GEOTECHNICAL TESTING LABORATORY
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.
BUILDING SETBACK
A building setback from landslide hazard areas is
required unless evaluated and reduced by an
engineering geologist or a licensed professional
engineer. Based on our geotechnical evaluation
of the site and our experience in the area, a
building setback will be needed for this lot. A
setback of 20-feet from the crest of the
southwestern slope to the bottom of the footing setback
should otherwise be observed. The building
setback may be measured from the bottom of the
footing to the face of the steep slope in
accordance with the Unified Building Code.
Peak Shear Stress vs. Normal Stress
Gravelly Sandy Loam
42-
25000
a 2000
d
15M
� I
t
W
0 1000
a_
500
—♦ 114 ton
�1f2 ton
—t 1 ton
0
0 500 1000 1500 2000 2500 30M
Normal Stress(p4
10011 Blomberg Street SW, Olympia,WA 98512 7
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GEOTECHNICAL TESTING LABORATORY
Slope stability was modeled using the GEO-SLOPE/W program (version 5.18) in both static and extreme dynamic
conditions (ca=0.3). Factors of safety were determined using Bishop's, Janbu, and the Morgenstern-Price methods.
The site was modeled using a monolithic layer. The gravelly sandy loam was determined to have a unit weight of
132 pcf, cohesion of 200 psf, and a shear angle (+) of 42°. Under static conditions, the slopes remained stable to
deep-seated and shallow failure. Under dynamic loading, the 3328 computations demonstrated that the slope is not
susceptible to surficial raveling. Large deep-seated failure was not demonstrated by our model. The following
figure illustrates a moment F.S. of 1.33, the lowest value derived from modeling the proposed building location.
This solution of greatest concern exhibits the need for a building setback of 20-feet.
Selleg Site — Slope A
Analysis Method: Morgenstern-Price • • • • • • �
Direction of Slip Movement: Left to Right C
Slip Surface Option: Grid and Radius
Seismic Coefficient: Horizontal and Vertical
a
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o � 1.5tf
330 1.33 .
320 \ A . . . . .
310
C 300
0 290 Alderwood Soil
M 280 Soil Model:Mohr-Coulomb
m Unit Weight: 132
W 270 Cohesion:200
260 Phi:42
250
0 25 50 75 100 125 150 175 200 225 250
Distance (ft)
As previously discussed, weathering, erosion and the resultant surficial sloughing and shallow landsliding are
natural processes that affect slope areas. No significant surficial raveling or sloughing was observed onsite. To
manage and reduce the potential for these natural processes, we recommend the following:
1. No drainage of concentrated surface water or significant sheet flow onto the sloped areas.
2. No filling within the setback zone unless retained by retaining walls or constructed as an engineered fill.
3. Trees may be removed on sloped areas as long as the stumps remain.
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).
10011 Blomberg Street SW, Olympia,WA 98512 8
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GEOTECHNICAL TESTING LABORATORY
Based on the subsurface conditions observed at the site, we interpret the site conditions to correspond to a seismic
Soil Profile Type C, for Very Dense Soil, as defined by Table 1615.1.1 (IBC). This is based on the range of SPT
(Standard Penetration Test) blow counts and/or probing with a ''/2-inch diameter steel probe rod. The shallow soil
conditions were assumed to be representative for the site conditions beyond the depths explored.
Based on our review of the subsurface conditions, we conclude that the site soils are only mildly susceptible to
liquefaction. The near-surface soils are generally in a dense condition and the static water table is located well
below the surface. Shaking of the already dense soil is not apt to produce a denser configuration and subsequently
excess pore water pressures are not likely to be produced.
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426
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 natural vegetation should be minimized and limited to the active construction areas. Yard landscaping
around the home is permissible, but understory growth on the slopes should be encouraged as much as possible as a
deterrent to erosion. 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.
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 8 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 1 foot 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.
10011 Blomberg Street SW, Olympia,WA 98512 9
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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
removal of vegetation and topsoil stripping is 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.
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 5 percent (by weight) passing the No. 200 sieve
based on that fraction passing the'/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 ON-SITE Sons AS FILL
On-site soils may not be considered for use as structural fill. In general, the native soils (sand and loam)
encountered on the site probably have more than 10 percent fines (material passing the US No. 200 Sieve) and are
not 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.
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Temporary cut slopes will likely be necessary during grading operations. As a general guide, temporary slopes of
1.5 to 1 (horizontal to vertical) or flatter may be used for temporary cuts 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 the
cut away from the top of the slope and that significant seepage is not present on the slope face. Flatter cut slopes
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 to
facilitate the development of a protective vegetative cover or otherwise protected.
FOUNDATION SUPPORT
Where foundation elements are located near slopes of 5 and 30 percent,the footings should be located a minimum of
2 times the footing width from the slope face (horizontally), and founded in medium dense or denser native soils or
properly prepared structural fill.
We recommend a minimum width of 2 feet for isolated footings and at least 14 inches for continuous wall footings
or according to the UBC. Footings founded as described above can be designed using an allowable soils bearing
capacity of 2000 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 be
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 friction between the
concrete and the underlying soil. Passive pressure may be determined using an allowable equivalent 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 for the
anticipated load conditions, with differential settlements between comparably loaded footings of '/2 inch or less.
Most of the settlements should occur essentially as loads are being applied. However, disturbance of the foundation
sub-grade during construction could result in larger settlements than predicted.
FLOOR SLAB SUPPORT
Slabs-on-grade should be supported on medium dense or dense native soils or on structural fill prepared as described
in the "Structural Fill" section of this report. We recommend that floor slabs be directly underlain by a minimum 6-
inch thickness of coarse sand and/or gravel containing less than 3 percent fines (by weight). The drainage material
should be placed in one lift and compacted to an unyielding condition.
A synthetic vapor barrier may be used for the control of moisture migration through the slab, particularly where
adhesives are used to anchor carpet or tile to the slab. A thin layer of sand may be placed over the vapor barrier and
immediately below the slab to protect the liner during steel and/or concrete placement. The lack of a vapor barrier
could result in wet spots on the slab, particularly in storage areas.
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i
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RETAINING WALLS
Retaining walls may be utilized on the sloping portion of the site to retain fill material. The lateral pressures acting
on the subgrade and retaining walls will depend upon the nature and density of the soil behind the wall. It is also
dependent upon the presence or absence of hydrostatic pressure. If the adjacent exterior wall space is backfilled
with clean granular, well-drained soil (washed rock), the design active pressure may be taken as 35 pcf(equivalent
fluid density). This design value assumes a level backslope and 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 a lateral
pressure, which includes the surcharge effects of the steep slope in proximity to the wall. Although not 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 upward from
the toe of the wall at an angle of 1 to 1 (Horizontal to Vertical) to a point where the line intersects the ground
surface. The surcharge effects may be modeled by increasing the equivalent fluid pressure for flat ground by the
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:1V 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 be
applied.
Positive drainage, which controls the development of hydrostatic pressure,can be accomplished by placing a zone of
coarse sand and gravel behind the walls. The granular drainage material should contain less than 5 percent fines.
The drainage zone should extend horizontally at least 18 inches from the back of the wall. The drainage zone should
also extend from the base of the wall to within 1 foot of the top of the wall. The drainage zone should be compacted
to approximately 90 percent of the MDD. Over compaction should be avoided as this can 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 base of
the wall to direct accumulated water to an appropriate discharge location.
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 can, with
time, 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. Passive pressure may be determined using an allowable
equivalent fluid density of 35 pcf(pounds per cubic foot). Factors of safety have been applied to these values.
10011 Blomberg Street SW, Olympia,WA 98512 12
Phone#: (360) 7544612 Fax#: (360) 754-4848
i ��
GEOTECHNICAL TESTING LABORATORY
RETAINING WALL ALTERNATIVES
Typically, reinforced-earth block wall systems are more cost effective for long-term walls than the other options.
r r request
Specific design criteria for these options can be provided at you eques 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 an appropriate infiltration area. We recommend that conventional roof drains be installed. Footing
drains shall be installed for the home and garage. The roof dram should not be connected to the footing dram. For
footing drains,the drain invert should be below the bottom of the footing.
We recommend that the collected stormwater runoff be directed to an infiltration galley located to the southeast of
the proposed building location, see Figure 2. 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 approved septic drainfield, (see Figure 2), is located where the slope is less than 5 percent. The septic drainfield
will not impact the slope and the slope will not impact the septic drainfield.
A .
9
T t View Looking Northeast at Septic Drainfield Location
`z
10011 Blomberg Street SW, Olympia,WA 98512 13
Phone#: (360) 7544612 Fax#: (360) 7544848
GEOTECHNICAL TESTING LABORATORY
LIMITATIONS
We have prepared this report for the use of Bruce Selleg 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 Laboratory and
its personnel cannot be responsible for unforeseen and widespread geologic events (such as earthquakes, large-scale
faulting, and mass wasting)beyond the scope of this project.
Variations in subsurface conditions are possible and may occur with time. A contingency for unanticipated
conditions should be included in the 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 those
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.
Oi Wash Respectfully submitted,
f07 GEOTECHNICAL TESTING LABORATORY
827 Harold Parks, L.G., L.E.G.
_ 'fed GE° Senior Engineering Geologist
HARC!J,ARKS
10011 Blomberg Street SW, Olympia,WA 98512 14
Phone#: (360) 7544612 Fax#: (360) 754-4848
I
G EOTECHNICAL
TESTING LABORATORY
Vicinity Map
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10011 Blomberg Street SW,Olympia,WA 98512
Phone#: (360)754-4612 Fax#: (360)754-4848
LT FABRIC W W
ROLLS
TERIAL
USEAR.SORAWIRERINGTOAE SR TALH
j FABRICTO HARE Geotechnical
/ FABRIC OR EQUIVALENT
7-01
Testing
10 1
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! 1 I 2-X4'WOOD POSTS,STANDARD OR BURY BOTTOM OF"
BETTER OR EQUAL ALTERNATE MATERIAL IN 8'X12'TREAICTH
! I I STEEL FENCE POSTS
1 I I
I 1 1
APPROVED
DRAINFIELD 1 ' 1 FILTER FABRIC r
O� LOCATION 1 FABRIC OR
GAUD IVA EE
1 1 ,
1 � 1 \ FABRIC OR EQUIVALENT Y P
1 1 \\
1 \ GROUND SURFACE 5-0.
\ \ PROVIDE&4P I VT WASTE
\ A \ ---_--_- GRAVEL BACK ILL INSIDES FFILT tY
\ M \ AND ON BOTH SIDR OF RLTHi
\ ' ` \\ FENCE FABRIC ON TIE SURFACE 8'MN
\ \
\ \\ 2'74P'WOODPOSIS
\ ` ALT STEEL FENCE POSTS Geotechnical Services
\ \` FlL11B'i FABRIC FBCE NOTES'.
\\ ` 1.FILTER FABRIC SHALL BE PURCHASED INACONI1NOUISHOU-CUTTO QA/QC Services
♦ - THE LENGTH OF THE BARRIER TO AVOIDUSE OF JOINTS.WREN JOINTS
ARE NECESSARY.FILTER CLOTH SHALL BESRICEDTOGERBROILYAT Testing Services
A SUPPORT\y FASTENED AT
OST WITH A MINIMUM 54NCH BOTH ENDS
THE POST. OVERLAP MA SECURELY 2.POSTS SHALL BE SPACED A THE
OF BFEET APART AND DRIVEN
'POTENTIAL i �� SECURELY INTO THE GROUND(MINIMUM OF 30W04M
3.A TRENCH SHALL BEEXCAVATEDAPPROAMATELYSINCIESWIDEAD12 10011 Blomberg St.SW
♦♦ J INCHES DEEP ALONG THE LINE OF PoSTS AND IDSLOFE FROM THE BARRIER.
INFIL—RATION ;; Olympia,WA 98512
`` ♦```♦ \\ P OTY WIRE STARES ATLEAST 1 INCH
POS LOCATION ; 1.WHEN FITSTANDARD STRENGTH FASTENED
FAESECURELY
URELY TO AWRE EUPSLSH
S HENST STANDARD
SHALL HFILTERF FABRIC IS
LYTO TEUPSLESH 90ETHE Phone:(360)754-4612
.1-ILL J / LONG,TIE WIRES OR HOG RINSTSUSING GS TEW1RE SHALL EMED INTO THE
`�\ `♦ \\ J / TRENCH A MINIMUM OF A I NICHES AND SHALL NOT EXIEDMORE THAN% Fax:(360)754OFPPO -4848
UIL DI NG INCHES ABOVE THE ORIGINAL GROUND SURFACE.
\ ♦♦\\ \` ' / 5.THE STANDARD STRENGTH FI LTER FABRI C SHALL BE STAPLED OR
` OCATION i i _ Designe /by: L 5
�♦ TO THE FEN E AN 20INCH FABRIC SHALL T ALL BE KTENCED
\ \ \ ! / / Designed by: LL
♦ \ \ \ / / INCHES ABOVE THE ORIGINAL GROUND SLfiFAGE.FILTER FAH3CSHALL
/ / NOT BE STAPLED TO THEENSRNG TREES Drawn by: LL
WHEN EXTRA.SRENGTH FILTER FABRIC AND CLOSER POST SPACING IS
` \�\ \ \ \\ \\ \\ / j / USED.THE WIRE MESH SUPPORT FENCE MAP BE EUMNATED.INSUCH
Checked by: LL
`�\ ` ♦\ \\ \\ \ \ / / / / j ACASE.THE FILTER FABRIC IS STAPLED OR WIRED ERECTLY TO THE Dwg#:01-26-05-010
♦♦♦ ♦ \ \ \\ \\ POSTS WITH ALL OTHER PROVISIONS OR ABOVE NOTES APPLYING
FILTER FABRC FNCES SHALL NOT BE
\\ ♦` ``\```\ \`\ \\ \` \\\ \\`\ \' FI L %/,/ //�//// / T AREA HAS BEIEN EPERMANENTLY STABILIZEDVID BEFORETHE UPSLOPE
` \
\\♦ `` `\`� \\♦\ \`♦\ \\\ \\\ \\\ \\\ \` \ \\♦ \ \ 5��� ,// //,//%/'/ /�/- ` 8 FILTER FABRIC L BE INSPECTEDIMMEDATE.Y AFTER EACH
RAINFFALL AND AT LEAST DAILYDURINGPROLONIGEDRAINFUL.ANY
`\ \\♦♦♦♦ ♦ ``♦ ♦\ \ \ \ \ \ \ \ \♦♦ ��`' , // / / , /// REQUIRED REPAIRS SHALL BE MALE IMMEDIATELY.
F_I L
\ ♦ . ,
/ `\♦♦ \ \\ `♦ ♦ \\ \\ \ ♦ \ \ ♦\ `\ ----- "-' / /// GENERAL EROSION COMg01 NOTES:
// `\\♦ \ ♦\ ♦♦ \ \\ \ \ `♦ \\ `♦ -'/ ,/,�/// 1 EROSIONR CONTROL MEASURES SHALL BE IN RACE PRIOR TO THE
/ \♦ ♦ \ \ ♦ \ \ \\ ``\ \ 310 BEGINNNGOFCONSUCTION THE PROJECT ENGINEER ADTECOUITY
T
/' ``\;♦ \\ \\ ♦♦ \\ \\ \ \\\ \\ \ \`� `\ \` ///,///'/- SHALL INSPECT AND APPROVE EINSTALATION OF
\♦ \♦ \ ♦ ♦\ ♦ \♦ \ \ \ - // EROSION CONTROL MEASURES PRIOR TO BEGINNING CONSTRUCTION.
/'' ♦`♦\\♦\\\\\\♦ `♦ \`♦ \`\ \`\\\ \ _.-_---"__-""� /// ,/ //// 2.EROSION CONTROL MEASURES ARE NOT UMITEDTO THE ITEMS
ONTMSPLAN.THE CONTRACTOR IS RESPONSIBLE FOR TIE
\ ♦ \ ♦ ♦ ♦ ♦ ♦ ♦ ♦\ i /' - / //j INSTALLATION AND MAJNTAJNANCE OF ALLEROSON CONTROL AEAA.RESEASTING OR .
``♦♦♦\♦\` ♦ \ ` ♦♦♦ \`♦ ``\ \ ` ----------"-"- /,//' ///��, AINAGE FACILITIES
SHALL BE ALLONO SILTATION OF
WED.CARE SHALLA�IBN�TO PREVEii MIGRATION
'/ \;;:: ,`, • •\ \ `, \ - _ __ OF SILTS TO OFF 9TECARE SHIESALL
PROJECT NAME:
\ 3.THE CONRACTORSHALL MAKE DAILY SURVBLL/NCEOFN.LEPOSON SELLEG SITE
`\\\\`\♦♦ `♦\ ♦♦ ♦� `\ \ \� 300 " " ,,/,, / CONTROL MEASURES AND MAKE ANY NECESBMI'REPNRS OR ADDITIONS 1050 EAST JENSEN ROAD
\�♦♦ \ ♦\ ♦ ♦ \ `� - / /,i, , TO THE EROSION CONTROL MEASURES.THE CONTRACTOR SHALL PROVIDE
♦♦�♦♦♦ ♦\ ♦\ ♦\ \\ `�\` - "� ADDITIONAL EROSION CONTROL MEASLRESASDETERMINEDN:CESSARY
♦�\♦\♦♦\ ♦ ♦♦ ♦ - ''------- -,�:�!/,// BY THE COUNTY IN ANDrOR THE PROJECT EJGIHFHT.FAILURESHELTON, WASHINGTON
.�\ \ \ ♦ ♦ \ - i TO COMPLY WITH ALL LOWLTAD STATE EROSION CONTROL
♦��♦ ♦ `♦ \ �♦ -----' /�/'/ / REQUIREMENTSMAYREC INCIMLPFNALTIESEEINGLEMED PARCEL 321322200010
♦ /
\♦♦� `♦ � ` - - � ,�///- AGAINST THE CONTRACTOR AND/OR PROJECT OWNER
// ���; ♦`\`\` ` �� -_--- / ,//i/'/i'/ 4.DURING THE WET SEASON(NOVEMBER TO MARCH)ALL LYSRRRBED COILS
♦ \�\ ------' , ,/ ,ice/ SHALL BE STABILIZED WITHIN 48 HOURS AFTER STOP OFWORK EROSION
�,♦ . ,,,;,,/ Revisions:
/'' \\�"\♦♦ - 290 /,/,/'//i// COVERNGATHEEFFECTED AREA IUTAWNG SPOIL RLESWITHH
♦♦`♦`� - -i�i,/ PLASTIC SHEETING,STRAW MATTING.JUTE MATTING,STRAW MAD/.
♦♦♦ - - OR WOODCHIPS.SEEDINGOFTHE DISRARBEDAEAS 9ULL TAKE
- -` ------." PLACE AS WEATHER PERMITS.
AREAS SHALL BE CHECKED REGULARLY
/-- - --_-_-_- ---" ♦�P 5.ALL TO MAKE SURE VEGEETATVE COVERAGEIISCOMEIE.AREASSUILBE
--- 280 - / REPAIRED,RESEEDED.ANDFERTIUZEDASREQURED.
NORTH '`9
TRACKING OF Sal OFFSITE WILL NOT ff I11PNED.IF ANY SOIL IS
SCALE I'-40' STREET
TITSHAULDEGOVEDEYTHEEND
NTY
�ONTO A DK YNYF MERK?ONGOFOMLLTE N
BEC.I.-2' �/ PREVENTED By SWEEPING
10_ R WASHING OF THE VE46ES TIRES
'// BEFORE DRIVING ON A COUNTY STREET
DATUM ASSUMED .
THIS IS ASSUMENOT A SURVEY -- _-� 7.NO MORETHAN 500LF OF TRENCH ON ADOWTSLOPEOFMORETIMIS
----�" PERCENT SHALL BE OPENED AT ONETIME.
` S.EXCAVATED MATERIAL SHALL BE PLACED ON THEUPHILL SCEOFTRENCES.
p 10 20 30 40 O
S.TRENCHADVERSELY
AFFECRING T
VICESFLOWING
SHALL EA S DH DRAINAGE
STEMS O THATVALL
NOT ADVERSELY AFFECT FLOWING STREAMS.aiALN/ViE SYSTEMS OR
' OFFSITE PROPERTIES. SCALE:1 Inch 40 f99t
i -
10.ALL STORM SEWER INLETS RECE VING RUNOFF FROM THE PRO�R,'TDLRING
/ CONSTRUCTION SHALL BE PROTECTED SO THAT SEDIMENT-LADEN WATER
WILL BE FILTERED BEFORE ENTERING THE CONVEYANCE SYSTEM
11.ALL OFF.STE CATCH BASINS IMMEDIATELY ADJACENT TO THE SITE
SHALL BE DISTURBED
ECTED AREAS
BLTATDN FIGURE 2
12.ALL DISTURBED AREAS SHALL BE SEEDED OR SCCDEDLFa1 COARl;TIOIR
OF WORK THE CONTRACTOR SHALLBERB.PCNSB.ETOBHSIRE TUT
COMPLETE COVERAGE OF THE DISTURBED AREASIS FROMCED&TUT
N IS
GROWTHBASINS
TRAP SEDIMENT RF1LT SITE PLAN
SI
13 CATCH UNDER GRATE
RNTILV SEDIMENT ORFl ESTABBRICMUSR BE
PLACED UNDER GRATE UNTIL VEGETATION IS ESTAB.ISHED.
1/2 INCH MINIMUM DIAMETER STEEL ROD
(STRAP)CLAMPED SECURELY TO PIPE
CORRUGATED TIGHTLINE 4 INCH
R MiNiM� MINIMUM,6 INCH SUGGESTED
RV / Sp M�o p
�iN� FT
F
TIGHTLINE ANCHORED WITH TWO,
3 FOOT REBAR LENGTHS OR BOLTS.
JLFRE END SECTION
QUARRY SPALL +a-T OR ENERGY
DISPERSION DEVICE
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
Gectechnical Services +"e'VA 0z sv FIGURE 3
QA/QC Services Phone:(W)7SC4612
Testing Services F-:(M)75446e6 Nat to scale DRAINAGE DETAILS