HomeMy WebLinkAboutGeoTech Review for BLD2007-01346 - BLD Engineering / Geo-tech Reports - 9/4/2007 ALKAI CONSULTANTS, LLC.
Environmental Engineering • Geotechnical Engineering • Wetland Consulting
September 4, 2007 TO BE KEPT IN THE ACL07-06-G179.019
PARCEL FILE
Mason County Department of Community Development
P.O. Box 279 RECE !
Shelton, WA 98584 j
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:EPO 5 2007 F
Attn: Ryan Crater _
Geotechnical Report Review MCCD - PLANNjN,-'- f[
Permit#BLD 2007-01346
Applicant: Dew
Dear Mr. Crater:
At your request, we have reviewed a Geotechnical Report for the above referenced permit. The report was
prepared by Geotechnical Testing Laboratory (GTL) dated March 7, 2007. The report was signed and stamped
by Harold Parks, L.E.G. (License# 827).
The report contains the information required in the Mason County Resource Ordinance, Geologically Hazardous
Areas 17.01.100.E.5.
We recommend that Mason County accept the report.
Should you have any questions or concerns, or if we may be of additional assistance, please call our office at
(360) 613-2407 or contact us by e-mail at Todd@alkai.net.
Sincerely,
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Todd S. Parkington, P.E.
Senior Geotechnical Engineer r
Attachments: Geo Tech Work Order isrE�V
Geotechnical Report by GTL ` ?X AT tires
EX�IRrG r/0j/�k+1
9465 Provost Road NW, Suite 202 • Silverdale,Washington 98383 • (360) 613-2407 • Fax: (360) 613-2408
TO BE KEPT IN THE
PARCEL FILE
GEOTECHNICAL REPORT
8940 EAST STATE ROUTE 106
UNION, WASHINGTON
PREPARED FOR
DAVID DEW
BY
GEOTECHNICAL TESTING LABORATORY
OLYMPIA, WASHINGTON
MARCH 7, 2007
GEOTECHNIC'AL TESTING LABORATORY
CONTACT INFORMATION
PREPARER INFORMATION
GTL PROJECT NUMBER: 07-0085
CONTACT: LANCE LEVINE
ADDRESS: 10011 BLOMBERG STREET SOUTHWEST
OLYMPIA,WASHINGTON 98512
TELEPHONE: (360)754-4612
FACSIMILE: (360)754-4848
EMAIL ADDRESS: GEOTESTLAB@COMCAST.NET
CLIENT INFORMATION
CLIENT: DAVID DEW
TELEPHONE: (206)525-3018
FACSIMILE: (206) 525-0661
BILLING ADDRESS: 6851 51ST AVENUE NE
SEATTLE,WASHINGTON 98115
SITE ADDRESS: 8940 EAST STATE ROUTE 106
UNION,WASHINGTON 98592
PARCEL: 322353100240
GPS LOCATION: N470 21.048' W 1230 01.884'
10011 Blomberg Street SW,Olympia, WA 98512 2
Phone#: (360) 754-4612 Fax#: (360)754-4848
GEOTECHNICAL TESTING LABORATORY
SCOPE OF UNDERSTANDING
DAVID DEW
6851 51ST AVENUE NE
SEATTLE,WA 98115
RE: GEOTECHNICAL REPORT
8940 EAST STATE ROUTE 106
UNION,WA 98592
PARCEL 322353100240
N470 21.048' W 1230 01.884'
Mr. Dew:
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.
Soil samples were submitted for laboratory testing from the project site. The data has been carefully analyzed to
determine soils bearing capacities, footing embedment depths and building 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.
We are also a full service laboratory that can meet all your building, testing (compaction, asphalt, concrete), and
special inspection needs. 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.
o� Was h� Respectfully Submitted,
10
' GEOTECHNICAL TESTING LABORATORY
Engineering \�. Sen or
s Engineering Geologist
e�Sed Geolo
HAROLD PARKS
efrwt5 -141.61
10011 Blomberg Street SW,Olympia,WA 98512 3
Phone#: (360) 754-4612 Fax#: (360)754-4848
GEOTECHNICAI,L TESTING LABORATORY
TABLE OF CONTENTS
CONTACT INFORMATION.....................................................................................................................................2
SCOPE OF UNDERSTANDING...............................................................................................................................3
TABLEOF CONTENTS............................................................................................................................................4
INTRODUCTION.......................................................................................................................................................5
SITECONDITIONS...................................................................................................................................................6
SurfaceConditions..................................................................................................................................................6
SiteGeology............................................................................................................................................................7
SiteSoils.................................................................................................................................................................8
SubsurfaceExplorations.........................................................................................................................................9
SubsurfaceConditions............................................................................................................................................9
SlopeStability.........................................................................................................................................................9
CONCLUSIONS AND RECOMMENDATIONS.................................................................................................... 11
General.................................................................................................................................................................. 11
GEOLOGICALLY HAZARDOUS AREAS............................................................................................................ 11
Landslide Hazard Classification........................................................................................................................... 11
Seismic Hazard Classification.............................................................................................................................. 12
Erosion Hazard Classification.............................................................................................................................. 12
SlopeStability....................................................................................................................................................... 13
BuildingSetback................................................................................................................................................... 14
Seismic—Liquefaction Hazard............................................................................................................................. 15
ErosionControl..................................................................................................................................................... 16
EARTHWORK......................................................................................................................................................... 17
SitePreparation..................................................................................................................................................... 17
StructuralFill........................................................................................................................................................ 17
Suitability of Onsite Soils as Fill.......................................................................................................................... 18
Cutand Fill Slopes................................................................................................................................................ 18
FoundationSupport............................................................................................................................................... 19
FloorSlab Support................................................................................................................................................20
RetainingWalls..........................................................................................................:..........................................20
RetainingWall Alternatives..................................................................................................................................21
SiteDrainage.........................................................................................................................................................22
SepticImpact.........................................................................................................................................................22
LIMITATIONS.........................................................................................................................................................22
Figure1 Vicinity Map...........................................................................................................................................24
10011 Blomberg Street SW,Olympia, WA 98512 4
Phone#: (360)7544612 Fax#: (360)754-4848
GEOTECHNicAL TESTING LABORATORY
INTRODUCTION
This report summarizes the results of our geotechnical consulting services for the proposed replacement of the
single-family residence. The site is located along the north-facing hillside overlooking the Hood Canal in Mason
County. The site is approximately 3.2 miles east of Union, Washington. The location of the site is shown relative
to the surrounding area on the Vicinity Map, Figure 1.
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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 by replacing the existing single-family residence. The site will
be accessed by an existing driveway from East State Route 106. In general, grading will consist of the excavation
of the foundation, footings, and septic drainfield. The approximate layout of the site is shown on the Site Plan,
Figure 2.
The site slopes toward the north from the proposed building location. The steepest slope measured onsite was
over 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.
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
Phone#: (360)754-4612 Fax#: (360) 754-4848
GEOTECHNIC L 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 along the southern shore of the Hood Canal. The site has a northern exposure. We conducted a
reconnaissance of the site area on February 15 and 23, 2007. Site elevations range from approximately 25 to 135
feet.
The building area of the site has vegetation common to the Northwest. The vegetation includes fir, madrone,
alder, cedar, hemlock, and maple trees as well as Scot's broom, Oregon grape, huckleberry, sword fern,
blackberry,holly, ivy,devil's club,and grasses.
At the time of the site visit, we observed no evidence of active surface erosion. No evidence of deep-seated slope
instability was observed onsite. Raveling and sloughing was observed along the toe of the southern slope. Offsite
to the west is an exposed slope, possibly due to an old borrow location.
Surface water flow was not observed onsite. The general topography of the site area indicates that drainage flows
toward the north toward the proposed building location.
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10011 Blomberg Street SW,Olympia, WA 98512 6
Phone* (360) 754-4612 Fax#: (360) 754-4848
GEOTECHNICAL 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 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 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.
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The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan (2003) describes the southern
site as 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
Phone#: (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
Alpine outwash,pre—late Wisconsinan (Pleistocene). The alpine outwash(Qapo) is described as:
Stratified sand, gravel, and cobbles; in the Quinault basin, clasts consist of sandstone and less-
abundant basalt from the Olympic Mountains core and peripheral rocks; in streams draining the
southern and southeastern Olympics, clasts consist primarily of Crescent Formation basalt with
less-abundant Olympic-core sandstone; may include peat, silt, and clay, and may be capped by
weathered loess; clasts are generally more rounded than those in till and lack facets and
striations;poorly to moderately sorted;gray to subtle yellow with wispy orange weathering.
The Geologic Map of Southeastern Mason
County, Washington, USGS Water-Supply
Bulletin 29 by Noble and Molenaar (1970)
describes the site 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 gp.m) of water
where gravel and coarser sand facees
below water table. '
SITE SOILS
The Soil Survey of Mason County, Washington, USDA Soil Conservation Service(1960)has mapped the northern
site soils as Everett gravelly loamy sand, 5 to 15 percent slopes(Eh). The survey describes the soil as follows:
This is the most extensive Everett soil. In undisturbed forests I to 2 inches of very dark grayish-
brown material, a mixture of needles, leaves, twigs, cones, moss, and roots, covers the surface.
The surface soil is loose, single-grained, pale-brown, gravelly sandy loam, 6 to 8 inches thick.
The upper 2 or 3 inches normally contains aggregates that are slightly hard and redder than the
others in the layer. To depths ranging from 18 to 24 inches, the subsoil is loose, single grained,
light yellowish-brown gravelly sandy loam or gravelly loamy sand. The amount of shot decreases
with depth; in the lower part only a few shot occur. The subsoil grades to a substratum of poorly
assorted, predominantly yellowish-brown sand, gravel, and cobbey material that is extremely
loose and porous. However, in places, this material will stand in banks. The color of this
material is largely determined by the gravel, course sand, and cobbles which are olive gray,pale
olive,yellowish brown, light brownish gray, gray, and dark gray. Many of the cobbles, as well as
much of the gravel, are faintly to moderately stained by iron. The amount of gravel ranges from
about 20 percent to 50 percent in the subsoil to as much as 80 percent in the substratum. The soil
is medium to strongly acid and becomes less acid with depth.
The Soil Survey of Mason County, Washington, USDA Soil Conservation Service(1960) has mapped the southern
site soils as an Alderwood gravelly sandy loam, 30 to 45 percent slopes(Ad), at the site. The report reads:
The Alderwood soils typically formed from gravelly glacial till. 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.
10011 Blomberg Street SW,Olympia, WA 98512 8
Phone#:(360)754-4612 Fax#: (360)754-4848
GEOTECHNICAL, 'TESTING LABORATORY
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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 was not encountered at the proposed building location and is beyond the scope
of this report. Depth to competent soil is approximately 12 inches throughout the proposed building location.
SUBSURFACE CONDITIONS
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In general, dense de ood g ave y sandy loam was observed in the undisturbed portions of the site. Vashon
Stade glacial material was observed below the Alderwood material. Groundwater was not observed or
encountered. Groundwater seepage was not observed onsite. 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.
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SLOPE STABILITY
The Relative Slope Stability of the Southern Hood Canal Area, Washington, (1977)describes the site area as Class
2. Class 2 is described as:
Areas believed to be stable under normal conditions, but may become unstable if disturbed by
man's activities, if slope is oversteepened by erosion, or if subjected to strong seismic shaking.
Slopes generally steeper than 15 percent, but may be less in some areas of weak geologic
materials. Includes areas underlain by: well-drained sand and gravel, mostly on valley sides
that lack known slope failures;glacial till with steep slopes; and bedrock.
10011 Blomberg Street SW,Olympia, WA 98512 9
Phone#: (360)754-4612 Fax#: (360) 754-4848
GEOTFCHN C L TESTING LABORATORY
The Coastal Zone Atlas, Volume 9, Mason County (MA-8) maps the site as Pleistocene gravels (Qpg). Slope
stability is described as "intermediate" at the building location and throughout the site. The chance of flooding is
less than one percent. The advance outwash is further described at having"good to excellent foundation support,"
"good seismic stability,"and"generally stable in slopes up to angle of repose."
Slopes over 100 percent were observed onsite. Since S� U" A
slopes of 40 percent or greater with 10 feet or more of �
5
vertical relief occur onsite, Mason County requires that s
a geotechnical report be completed according to the s
Critical Areas Ordinance. 7
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The near-surface soils are in a dense to very dense 5
Scab is:..a
condition except at the ground surface. The surficial oo
soils are generally in a medium dense condition.
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In general,the undisturbed native soils of the site consist
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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 5
activity. No evidence of deep-seated landslide activity '
or significant erosion was 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 observed along the southern road cut.
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
Phone#: 360 754-4612 Fax#: 360 754-4848