HomeMy WebLinkAboutBLD2005-00057 Geotechnical Report • •
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STRATUM GROUP
1451 Grant Street,Bellingham, WA 98225
Phone(360)714-9409
November 4, 2002
Ron Simpson
Covenant Mortgage Corporation
9725 SE 36th
Suite 304
Mercer island, WA 9840-;84O
Re: Geology Evaluation
Lot 1, Sugar Hill Estates
Section 13, Township 29 N,Range 1 W
Jefferson County,Washington
Dear Mr. Simpson:
We are pleased to present the results of our geology evaluation of the above referenced property.
The western portion of the lot consists of a steep potentially unstable slope. The purpose of this
geology evaluation was to 1) determine the suitability of the property for the siting of a residence,
2)qualitatively evaluate the risk of slope failures, and 3)provide general site development and
maintenance recommendations for development of the property adjacent to a potentially unstable
slope. This evaluation was limited to a visual inspection of the property and vicinity, a visual
inspection of the steep slopes on the property and in the vicinity of the property, and review of
available geologic mapping in the area.
SCOPE OF SERVICES
The scope of our services included the following:
1) Conducted a site visit to visually inspect the subject property including the steep
slope conditions and relevant conditions in the vicinity of the property.
2) Observed surface soil conditions on the steep slope and on the uplands above the
slope by excavating shallow hand dug test pits.
3) Prepared this report summarizing our findings, including an evaluation of the
feasibility of building a residence on the subject property, a qualitative evaluation
of the slope stability, recommendations for site development, and
recommendations for further investigation, if necessary.
i i
November 1,2002
Lot 1, Sugar Hill Estates
Geology Hazard Evaluation
GENERAL GEOLOGY
Northwestern Washington has been occupied by continental glaciers at least four times during the
Pleistocene Epoch(1.6 million to 10,000 years ago). During these glacial and accompanying
interglacial periods, the underlying bedrock was eroded and a relatively thick layer of glacial
related and interglacial fluvial sediments were deposited over the underlying bedrock in the
vicinity of the subject property.
The Surficial Geologic Map of the Port Townsend 30-by 60-Minute Quadrangle, Puget Sound
Region, Washington(Pessl,Deither,Booth and Minard, 1989)indicates the subject property is
underlain by two units: 1) Glacial and nonglacial sedimentary deposits of Pre-Fraser Glaciation
age and 2)glacial till. The Geologic Map Surficial Deposits in the Seattle 30' x 60' Ouadrangle,
Washington (Yount,Minard, and Dembroff, 1993) indicates the subject property is underlain by
glacial till and the Pre-Frasser Glaciation sediments consist of undifferentiated Pleistocene
deposits and Possession Till.
The pre-Fraser glaciation deposits are described as consisting of interbedded oxidized brown,red-
brown, and gray gravel, sand, silt, and clay. The layers are moderately to well bedded and the unit
contains minor amounts of ice-contact deposits and outwash gravel and sand. Generally the unit is
nonglacial and has abundant peat and woody debris. The two glacial tills consist of a poorly
sorted mixture of rock fragments ranging in size from clay, silt, sand and gravel and cobbles
deposited directly by glacial ice.
Observations on the steep slope and upland area of the subject property are consistent with the
mapping described above except that a relatively thin deposit of loose glacial recession sand and
gravel is present on the uppermost slopes and upland area of the subject property. The steep slope
is for the most part underlain by very compact silt(Pre-Fraser deposits)and glacial till. Glacial till
was observed near the top of the slope and near the base of the slope. The till near the base of the
slope is likely the Possession Till.
The property is located on the east side of Chimacum Valley. The valley is a glacial valley created
during the last ice age. The valley was formed by the erosion of pre-Fraser deposits by the Vashon
ice sheet and/or water flowing underneath the glacier.
SPECIFIC SITE OBSERVATIONS
The site location map is provided on Figure 1 and a general site plan sketch is provided on Figure
2. The subject property consists of an upland area bounded on the west by the steep slope of
Chimacum Valley. The elevation of the upland is approximately 380 feet and the base of the steep
Stratum Group
File:10.6,02B
4111
November 1,2002
Lot 1, Sugar Hill Estates
Geology Hazard Evaluation
slope is at an elevation of approximately 150 feet.
A level building pad has been constructed on the upland of the property near the top of the steep
slope. The west edge of the building pad is located 34 feet from the top of the steep slope. The
steep slope slopes downward from the upland area at an angle of approximately 35 degrees. The
slope is well vegetated with a mix of trees and thick brush. Portions of the slope are steeper
because a number of old logging skid roads have been cut into and switch back and forth up the
slope. Except for minor sloughing of cut slopes and topsoil creep, no evidence of slope failures
was observed on the steep slope. The entire steep slope is underlain by very compact silt, sand,
and gravel deposits and glacial till. Based on the age of the trees on the slope, we estimate that the
slope was clear cut approximately 40 to 50 years ago.
The upland area of the property consists of relatively gentle slopes with one south slope created
by the cutting of an access road through a small ridge located near the top of the steep slope.
Except for the building pad area and the area in the immediately in the vicinity of the proposed
building area, the upland portion of the property slopes gently to the east away from the steep
slope.
No water seeps were observed on the steep slope and no seasonal wet areas are present.
We did not observe any evidence(tension cracks or trees rotated inward away from the top of the
bluff or indications of past uplift of the beach area)indicating an incipient global-type or deep-
seated failure on the subject property.
CONCLUSIONS AND RECOMMENDATIONS
Based on our visual inspection of the subject property, we conclude that the steep slope on the
west side of the property is relatively stable and is only subject to minor topsoil and slope
sloughing. A residence can be located on the proposed building pad as long as it is located 5 feet
back from the west edge of the building pad.
A residence can be built within the area indicated on the Figure 2 Site Sketch Map. It is our
opinion that a residence located within the area indicated on Figure 2 will be at minimal risk of
being impacted by landslides.
We do not anticipate that the development of the subject property will cause any negative impacts
on the stability of the slope as long as our recommendations are followed.
Soils on the upland portion of the property appear to be relatively well drained, and therefore we
Stratum Group
File:10.6.02B
November 1,2002
Lot 1, Sugar Hill Estates
Geology Hazard Evaluation
do not anticipate discharging of footing drains will be necessary. Roof drainage and any storm
water catch basins must not be introduced into the perimeter footing drain. We recommend that
any storm water generated be discharged into a rigid perforated dispersion pipe or dispersed on
the forest floor to the south of the proposed building site and access road. If a dispersion pipe is
used,it should be placed in a level infiltration trench excavated perpendicular to the slope and
should be located at least 30 feet from the top of the steep slope.
Site grading soils or debris, landscape debris, or any other material should not be disposed of over
the steep slope or placed at the top of steep slope.
Trees on the steep slope may be limbed for view purposes, but no trees should be removed unless
a thinning or harvest plan has been reviewed by a geologist familiar with slope stability and tree
removal. Although the steep slope has previously been logged without causing obvious
landsliding,the slope stability may respond differently to second cut because of different forest
cover.
The proposed septic drain field is part of a community drain field to be used by several properties
and is located 400 feet northeast of the proposed building area. The septic drain field should not
cause problems for slope stability on the subject property or on any other properties as it is
located such that it will not effect slope hydrology.
Please note that there are inherent risks associated with building on lots near or adjacent to steep
slopes. These are risks that the building owner should recognize and be willing to accept. If
conditions appear different than those described in this report, or other concerns arise, we request
that we be notified so we can review those areas and modify our recommendations as required.
We appreciate the opportunity to be of service to you. Should you have any questions regarding
our reconnaissance please contact our office at(360) 714-9409.
Sincerely yours,
Stratum Group O ,t A-
•
Dan cShane, M.S.,P.E.G. (;,
Professional Engineering Geologist ', iC'\ =� 0 /
a
t+� 18764`1
Daniel McShane
Stratum Group
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After Recording Return to:
CLARK LAND OFFICE
P.O. BOX 2199
SEQUIM,WA 98382
Geotechnical Report
Sugar Hill Estates
Chimacum, Washington
February 1996
Submitted to:
Mr. Bill Lowry
P. O. Box 211
Chimacum, Washington 98325
By:
Shannon&Wilson, Inc.
400 N 34th Street, Suite 100
Seattle, Washington 98103
W-7182-01
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TABLE OF CONTENTS
Page
1.0 INTRODUCTION 1
2.0 SITE DESCRIPTION 1
3.0 PROJECT DESCRIPTION 2
4.0 EXPLORATIONS AND LABORATORY TESTING 2
5.0 SUBSURFACE CONDITIONS 3
6.0 CONCLUSIONS AND RECOMMENDATIONS 5
6.1 Slope Stability and Project Impact 5
6.2 Excavations and Site Grading 6
6.3 Pavement Recommendations 7
6.4 Wet Weather Earthwork 8
6.5 Drainage and Foundation Backfill 10
6.6 Foundations 10
6.7 Floor Slab Support 11
6.8 Lateral Earth Pressures and Retaining Structures 12
6.9 Erosion Control 13
7.0 ADDITIONAL CONSIDERATION-TEST PIT EXCAVATIONS 14
8.0 LIMITATIONS 14
TABLE
Table No.
1 Geotechnical Logs of Selected Septic Test Pits
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TABLE OF CONTENTS (cont.)
LIST OF FIGURES
Figure No.
1 Vicinity Map
2 Site and Exploration Plan
3 Log of Test Pit TP-1
4 Log of Test Pit TP-2
5 Log of Test Pit TP-3
6 Log of Test Pit TP-4
7 Log of Test Pit TP-5
8 Grain Size Distribution
9 Typical Rockery Detail
10 Subdrainage and Backfilling
APPENDIX
IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL REPORT
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GEOTECHNICAL REPORT
SUGAR HILL ESTATES
CHIMACUM, WASHINGTON
1.0 INTRODUCTION
This geotechnical report presents the results of our field explorations, conclusions, and
recommendations for the proposed residential development approximately one mile southeast of
Chimacum, Washington. Our work was conducted in general accordance with our proposal
dated October 23, 1995. A companion wetland delineation report, also prepared by Shannon &
Wilson, is submitted under separate cover.
The purpose of our work is to provide geotechnical engineering assessments and
recommendations for site development in accordance with Jefferson County Interim Critical
Areas Ordinance guidelines. Our geotechnical evaluations are based on a site reconnaissances
performed on November 8, 1995, subsurface explorations completed by November 8, 1995, and
geology and soil maps. Our understanding of the proposed subdivision layout and development
is based on site plans provided by Tillman Engineering, Inc. and Clark Land Office.
2.0 SITE DESCRIPTION
The proposed subdivision is located on approximately 50 acres on the east side of Beaver Valley
Road, approximately one mile southeast of Chimacum, Washington (see Figure 1). The site is
roughly 1,540 feet long(east-west)by 1,321 feet wide(north-south) with a 388-foot-long by
484-foot-wide rectangular area extending eastward at the northeast corner(see Figure 2). The
site includes a portion of the west facing Beaver Valley side and upland area east of the valley.
In general, the ground slopes up from the valley floor elevation of 100 feet in Beaver Valley
immediately west of the site, to a maximum elevation of over 405 feet on a northwest-southeast-
trending ridge in the southwest quadrant of the site. From the top of this ridge, the ground slopes
back down to the northeast to an undulating, upland surface that ranges in elevation between 365
and 250 feet. Although undulating, the upland surface generally slopes down to the north and
west to a ravine located in the northwest quadrant of the property that drains the upland to
Beaver Valley on the west. Slopes across the site range from less than 10 percent on many parts
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of the upland to 100 percent on portions of the valley wall and ridge at the southwest corner of
the site.
The property has been selectively logged over the past few decades. As a consequence, the
vegetation across the site consists of coniferous and deciduous trees (e.g., Cedar, Douglas Fir,
Maple, Alder) of various heights and diameters (up to about 2 feet in diameter). The
undergrowth has also been disturbed and ranges from dense salmonberries to sword ferns and
grasses.
During our November site visit, we observed growth positions of the trees on the sides of the
valley and ravine (southwest and northwest corners of the site,respectively), which indicate that
relatively slow soil creep is occurring on the steeper portions of these slopes. Soil creep occurs
on nearly all slopes and is the imperceptibly slow,downslope movement of soils under the
effects of gravity. In addition, the vegetation on the valley side includes Madrona with an
undergrowth of grass and salal, which are indicative of relatively dry, subsurface conditions.
Surface water was observed in a large pond located off the property along the east property line
(see Figure 2), and water flow of a few gallons per minute were observed in the ravine. Mr. Bill
Lowry indicated that his family had constructed the large pond. Signs of seepage and near-
surface water were also observed on the north side of the property. The occurrence of surface
water and wetlands are discussed in detail in the companion wetland delineation report.
3.0 PROJECT DESCRIPTION
The subdivision will include ten, 5.0- to 6.0-acre building lots for single-family residences, as
shown on Figure 2. Access to the lots will be by existing roads and easements indicated on
Figure 2. Minor realignment, grade changes,and widening are proposed for the existing road.
The dimensions of this pond have not yet been determined. Current plans do not call for the
construction of retaining walls or rockeries.
4.0 EXPLORATIONS AND LABORATORY TESTING
An engineering geologist from our firm conducted a geologic site reconnaissance on November
8, 1995, which included excavation of five backhoe test pits. The geotechnical test pits were
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designated TP-101 to TP-105, and their locations are shown on Figure 2 as surveyed by Clark
Land Office, The test pit locations were selected in the field to obtain subsurface information
across the site, in the different topographic features, in areas where differing soil conditions
might be expected to occur, and in areas where septic test pits had not been excavated or had
been excavated only to shallow depths.
Geotechnical test pit depths ranged from 6 1/2 to 11 1/2 feet. Soils exposed in the test pits were
logged, and relative densities or consistencies were estimated in the field by our engineering
geologist. Representative soil samples were collected in the field and returned to our laboratory
for further analyses. The logs for the geotechnical test pits are presented on Figures 3 through 7.
In our laboratory, soil sample classification was visually checked, and sample moisture contents
were determined. The moisture contents are indicated on each test pit log. Three grain-size
analyses were conducted on soil types that may be used for fill to aid in determining their
engineering properties and suitability for fill. These samples were selected for testing, as they
are non-organic soils within the upper few feet of the ground surface that may be excavated
during construction of footings, basements, utility trenches,etc. The results of the grain-size
analyses are presented on Figure 8.
The site reconnaissance also included logging existing,open test pits previously excavated for
septic design. The geotechnical descriptions and properties of the soils exposed in the septic test
pits are given in Table 1, and their locations are indicated on Figure 2.
5.0 SUBSURFACE CONDITIONS
Geologic maps of the area indicate that the valley side is composed of pre-Vashon stratified
sediment, and the upland portion of the site is underlain by Vashon lodgement till. Till is a non-
sorted mixture of clay, silt, sand, and gravel with scattered cobbles and boulders that is deposited
by a glacier. Lodgement till is deposited at the base of a glacier and is subsequently overridden
by the advancing glacier. The Vashon Ice sheet that deposited the lodgement till is estimated to
have been up to 4,000 feet thick in the area. As a result, the till and underlying pre-Vashon
sediments were overconsolidated to a very dense or hard state because of the great weight of the
ice.
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Both the geotechnical and existing septic test pits confirmed the presence of the lodgement till
beneath the upland portion of the site. Till was encountered in test pits TP-101,TP-102,TP-103,
and TP-105, and was observed in a number of the septic test pits and various road cuts in the
upland. The till encountered in the test pits is typically a very dense, slightly gravelly, silty sand
to sandy silt. In test pits TP-102,TP-103, and TP-105, the till was overlain by approximately 1
1/2 feet of relatively loose, silty, sandy topsoil. Below a depth of 1 1/2 feet, either dense
weathered till or very dense, unweathered till was encountered. Below a depth of 3 1/2 feet in
these three test pits,the subsurface soil was very dense, unweathered till.
In addition to the till,recessional outwash and recent alluvial deposits were found on the upland
area of the site. Both the recessional outwash deposit and recent alluvium were deposited after
the retreat of the last glacial ice in the area and are not glacially overridden. Based on our
interpretation of the field data, we have approximated areas of the site underlain by about 2 or
more feet of recessional outwash or alluvium, which are shown on Figure 2. The approximate
locations of these deposits were mapped based on soils exposed in both the geotechnical and
septic test pits, the site reconnaissance, and the topography.
Recessional outwash on the upland is a medium dense to dense gravel and/or sand material that
was deposited in an outwash plain near the terminus of the latest glacier as it receded to the
north. Alluvium has accumulated since the last glacial influence on the area in small pockets and
depressions left in the upland surface. Test Pit TP-I01 was excavated in one of these mapped
alluvial deposits and encountered approximately 3 feet of loose, silty sand (fill), underlain by
about 1/2 foot of loose, fine sandy silt(buried topsoil), in turn underlain by approximately 6 feet
of medium dense, slightly clayey, silty, fine sand (alluvium). At a depth of 9 1/2 feet,
immediately below the alluvium, a 1/2-foot-thick layer of dense gravelly sand with scattered
cobbles (recessional outwash)was encountered, which in turn was underlain by very dense/hard,
slightly sandy, slightly clayey silt with scattered gravel (till).
The presence of pre-Vashon stratified sediment along the valley side was confirmed in our site
reconnaissance. Hard, varved clay and silt were observed in road cuts in the ravine immediately
west of the northwest corner of the site and in log skidder cuts on the face of the valley side on
the west side of the property. The varved clay and silt were observed in cuts in approximately
the lower two-thirds of the valley wall (up to about elevation 300 feet).
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The soil exposed in cuts and septic test pits in the upper third of the valley wall and the ridge in
the southwest corner of the site appeared to be predominantly very dense fine sand with lenses of
fine sandy silt and gravelly sand. The sandy sediment that comprises this ridge located above the
varved clay and silt may be pre-Vashon and/or glacially overridden ice contact deposits. Test pit
TP-104, located at the base of the ridge on its northeast side, was excavated 9 1/2 feet and into
this sediment. Below the upper 1 1/2 feet of loose topsoil,4 1/2 feet of dense to very dense
slightly fine gravelly, fine sand was observed. Below the sand, between 6 and 6 1/2 feet below
the ground surface, very dense, gravelly sand was observed. Below 6 1/2 feet, very dense, fine
sandy silt was observed.
Groundwater seepage was observed in test pits TP-101 and TP-102 below depths of about 2 feet
and 1 foot, respectively. No groundwater was observed in test pits TP-103, TP-104 or TP-105.
6.0 CONCLUSIONS AND RECOMMENDATIONS
6.1 Slope Stability and Project Impact
Based on the subsurface conditions observed at the site and our experience with similar soils in
the Puget Sound area, it is our opinion that the existing slopes in the upland area are relatively
stable and,provided that the following recommendations contained in this report are
implemented, the impact of the proposed subdivision on the stability of the site and adjacent
slopes will be small. The steeper west-facing Beaver Valley side slopes are marginally stable
and should not be developed.
It is our opinion that reasonable development on site slopes flatter than 2 Horizontal to 1 Vertical
(2H:I V)may be accomplished with little impact on slope stability. Construction on or within 25
feet of slopes of 2H:IV or steeper should be avoided. No fill should be placed on these slopes.
Alternatively, additional geotechnical explorations and resulting studies may be performed for
specific structures planned on slopes 214:1 V or steeper. Explorations and studies would need to
address specific foundation types for the given structure and site development recommendations
to reduce the risk of slope movement. Slopes at this site that are 2H:1 V and steeper are Iocated
on the valley wall and the west side of the ridge at the southwest corner of the property and are
indicated on Figure 2.
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We note that the steep valley side and west ridge face along the west side of the site essentially
consists of sandy soils overlying relatively impervious silt and clay. Groundwater has a
tendency to perch on top of the silt and clay at the contact with the overlying sand. It has been
our experience that the presence of perched groundwater under these conditions greatly increases
the failure susceptibility of the slope. As previously noted,no signs of current slope instability
(other than soil creep)were observed, nor were seepage or vegetation indicative of near-surface
water observed on this slope. To maintain the present conditions on the slope, site development
should not increase the amount of water entering the soils on this slope, which would increase
the potential for water to perch at the sand and silt/clay contact. Therefore, we recommend to
not locate septic drain fields on this slope or on the upper portions of the ridge at the southwest
corner of the site. Landscaping and plantings for sites that may be developed on top of this ridge
should be planned so as to require minimal irrigation. Roof, footing, and yard drains should not
discharge onto the slope or ridge and should be routed to the base of the ridge or away from
ridge face. Additional recommendations regarding drainage are presented in the "Drainage and
Foundation Backfill" section of this report.
Please note that there is some risk of future instability present on all hillsides, which the owner
must be prepared to accept. Such instability could occur because of future water breaks/leaks,
uncontrolled drainage, lack of maintaining drains or vegetative cover, unwise development in
adjacent areas, or other actions,events,or unknown conditions on a slope that may cause sliding.
6.2 Excavations and Site Grading
It is our opinion that permanent excavations into the very dense/hard, glacially overridden soils
at the site (i.e. till,ice contact,pre-Vashon sediment)will generally be stable at slopes to about
1H:1 V. However, permanent slopes cut this steeply will ravel. It has been our experience that a
slope cut to 1.5H:1V in these soils would not ravel and would maintain vegetation. Permanent
slopes cut steeper than 1.5H:I V in these soils should be protected with rockeries. We
recommend that rockeries be no taller than 8 feet. Figure 9 provides additional detail and
recommendations for a typical rockery construction. Fill slopes and excavations made into other
soils at the site (i.e., recessional outwash and alluvium) should be sloped 2H:1V or flatter.
During construction, we recommend that the stability of the excavation slopes be made the
responsibility of the contractor, as he/she will be the one most familiar with conditions exposed
in the excavation and will be at the site on a full-time basis. The contractor should be
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responsible for following all current and applicable safety regulations regarding excavations,
shoring,etc. The contractor should also be responsible for the control of all ground or surface
water wherever encountered on the project.
All fill and/or backfill beneath pavements, slabs-on-grade, and other areas where settlements are
to be minimized, should be structural fill compacted to a dense, unyielding state, and to at least
95 percent of its Modified Proctor maximum dry density(ASTM: D 1557-70, Method C or D).
In areas where moderate settlements can be accepted, such as in non-structural landscape areas,
the compaction requirement could be reduced to a dense, unyielding condition and to at least 92
percent of the Modified Proctor maximum dry density. We recommend that the thickness of
fill/backfill layers before compaction not exceed 8 inches for heavy compaction equipment or 4
inches for hand-operated mechanical compactors.
The non-organic portion of the on-site soils can be used for fill/backfill if suitably compacted as
previously recommended. However, because of the relatively high silt content, most of the site
soils are moisture sensitive, making them difficult to work and to compact when wet. The
natural moisture content of these soils, as determined by tests on samples taken from the
geotechnical test pits (TP-101 through TP-105), was sufficiently high (for a number of samples)
to require drying/aeration before compacting. If earthwork is planned during the rainy season or
in wet conditions,it will likely be necessary to use imported,clean, granular fill rather than the
on-site soils. Additionally, exposing these soils to construction activity when wet will
substantially increase their erodability.
If imported soil is needed for fill/backfill,it should consist of clean, well-graded sand and gravel.
It should contain not more than 5 percent fines (soil passing the No. 200 sieve,based on wet
sieving the minus-3/4-inch fraction). The fines should be non-plastic. It should have a
maximum particle size of 3 inches, should be free of organic matter, and have a moisture content
at or slightly below its optimum for compaction.
6.3 Pavement Recommendations
If pavement is planned, we recommend that a total of at least 12 inches of pavement, base
course, and/or granular subbase be provided between the native site subgrade and the top of the
pavement. This approach will provide adequate frost protection. A minimum of four inches of
crushed rock should be placed immediately beneath the asphalt. The underlying granular
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subbase should consist of clean pit-run sand and gravel,well-graded crushed rock, or a blend of
commercial rock products, and contain not more than 3 percent material finer than 0.02 mm. It
should conform to the following gradation requirements:
Gradation for Sub-base
U.S. Standard Sieve Size Percent Passing By Weight
2 inches 100
1 inch 70-100
No. 4 35-65
No. 200 (by wet sieving) 3-5 (non-plastic)
Base and subbase should be thoroughly compacted to achieve a dense and unyielding surface,
and to at least 98 percent of its Modified Proctor (ASTM: D 1557-70, Method C or D)
maximum density.
Pavement subgrades should consist of stable, stiff to hard, or medium dense to very dense native
soil or compacted structural fill placed on these competent soils. All loose, soft, or disturbed soil
and all soil containing organics should be removed from beneath areas to be paved. In general,
this will require a 2-foot stripping depth for newly constructed roadways and drives; however,
strip as deep as needed to expose competent soils. We recommend that prepared pavement
subgrades be proof-rolled with a loaded dump truck or scraper prior to placement of base and
subbase materials. Existing gravel access roads that will be paved should also be proof-rolled
prior to placement of subbase. Soft or spongy materials identified during the proof-rolling
should be removed and replaced with cleaner and/or drier materials. Medium dense subgrades
should be compacted at the surface to achieve a dense, unyielding condition.
6.4 Wet Weather Earthwork
Wet weather generally begins about mid-October and continues through about May, although
rainy periods may occur at any time of the year. Therefore, it would be most advisable to
schedule earthwork during the normal dry weather months of June through mid-October.
Earthwork performed during the wet weather months will generally prove more costly.
As indicated previously, the soils at the site generally contain sufficient silt and plastic fines to
produce a cohesive, unstable and erodible mixture when wet. Such soils are highly susceptible
to changes in water content, and they become muddy, unstable, and difficult or impossible to
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proof-roll and compact if their moisture content significantly exceeds the optimum. The
condition of exposed dense/hard glacial till will soften rapidly when exposed to moisture and
construction activity.
It should also be noted that particularly during the wet weather months, groundwater levels
would be at their highest. Higher groundwater levels will increase the potential for groundwater
to seep into site excavations. The groundwater would need to be intercepted by drainage ditches,
trench drains, or otherwise removed. It is our experience that the presence of standing water
upon the till or other bearing layers containing silt or clay, along with construction activity, will
result in disturbance and softening of the subgrade. This could lead to deeper excavations than
possibly anticipated.
Earthwork in wet seasons is possible but usually adds considerable cost to site development due
to factors such as increased material cost and reduced labor efficiency. The following
recommendations are applicable if earthwork is to be accomplished in wet weather or in wet
conditions:
a. Earthwork should be accomplished in small sections to minimize exposure to wet weather. If
there is to be traffic over the exposed subgrade, the subgrade should be protected with a
compacted layer(generally 8 inches or more)of clean sand and gravel or crushed rock. The
size or type of equipment may have to be limited to prevent soil disturbance;
b. Fill material should consist of clean, granular soil, of which not more than 5 percent by dry
weight passes the No. 200 mesh sieve, based on wet sieving the fraction passing the 3/4-inch
sieve. The fines should be non-plastic. Such soil would need to be imported to the site;
c. The ground surface in the construction area should be sloped and sealed with a smooth-drum
roller to promote the rapid runoff of precipitation, to prevent surface water from flowing into
excavations, and to prevent ponding of water;
d. No soil should be left uncompacted and exposed to moisture. A smooth-drum vibratory
roller, or equivalent, should be used to seal the ground surface. Soils that become too wet for
compaction should be removed and replaced with clean granular soil;
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e. Excavation and placement of structural fill material should be observed on a full-time basis
by a geotechnical engineer, or his/her representative, experienced in wet-weather earthwork,
to determine that all unsuitable materials are removed and suitable compaction and site
drainage is achieved; and,
f. Covering of work areas, soil stockpiles,or slopes with plastic; sloping; ditching; installing
sumps; dewatering; and other measures should be employed, as necessary,to permit proper
completion of the work. Bales of straw and/or geotextile silt fences should be aptly located
to control soil movement and erosion.
6.5 Drainage and Foundation BackfiIl
For buildings that will eventually be constructed on the site, we recommend that footing
subdrains be installed along the outside perimeter of the structures and on the up-slope side of
continuous interior footings. Footing subdrains should consist of perforated or slotted,4-inch-
diameter,plastic pipe bedded in washed 3/8-inch pea gravel. Typical installation of these drains
is shown in Figure 10. Figure 10 also contains subdrainage and foundation wall backfill
recommendations. Most of the on-site soils will not be suitable for use as drainage sand and
gravel. Note that the perimeter subdrain invert should be located at least 18 inches below the
lowest adjacent grade or at the bottom of the footing, which ever is deeper. A drainage
geotextile should not be used around the subdrain pipe.
Roof drains should not be connected to flow into the footing subdrains. The discharge from
footing drains and roof drains should be routed by means of a tightline to a suitable discharge
point(i.e.,road ditches, storm sewers,etc.). Water should not be allowed to discharge onto the
surface of a slope or into slope soils. All hard surfaces around the structures should be sloped to
catch basins and the collected water disposed in a controlled manner. Perimeter grades around
structures should be sloped away from the structures.
6.6 Foundations
In our opinion, spread footings bearing in dense/very stiff or more competent soils at the site
(e.g., weathered till, ice contact, or pre-Vashon sediment) may be designed for 3,000 pounds per
square foot (psf) maximum allowable bearing pressure. Spread footings bearing in medium
dense soil (e.g., alluvium and recessional outwash shown on Figure 2) may be designed for 2,000
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psf maximum allowable bearing pressure. Stripping depths to reach bearing soils is about 2 feet
or deeper. Footings bearing within structural fill placed over the dense or very stiff soils could
be designed for allowable bearing pressures up to 3,000 psf; footings bearing in structural fill
place of medium dense soils should be designed for an allowable bearing capacity of 2,000 psf.
Continuous footings should have a minimum width of 18 inches, and column footings should
have a minimum width of 24 inches. Minimum footing widths may govern footing design.
Footings should bear at least 24 inches below the lowest adjacent grade. The bearing pressures
given above may be increased by one-third for seismic loading conditions.
If footings are supported by structural fill, this fill should extend beyond the outer edges of
footings a minimum distance equal to the fill thickness below the footing. If adjacent individual
footings are located at different elevations, it is recommended that the horizontal distance
between them be at least 1.5 times the elevation difference between their bases. Where adjoining
continuous footings are at different elevations, the upper footing should be stepped down to the
lower footing.
Foundation subgrades should be evaluated during construction to verify the presence of
competent bearing soil, and to determine that all soft or loosened, disturbed soils and all existing
topsoil have been removed. This evaluation should be made by a geotechnical engineer or
his/her representative.
Assuming compliance with the recommendations in this report,we expect settlement of
conventional spread footings to be no more than about 1/2 inch, with differential settlements
(between adjacent footings or over a 20-foot span of continuous footing)of approximately 1/4
inch, or less. Settlements would occur almost simultaneously with load application.
6.7 Floor Slab Support
Floors for future structures could be constructed as slabs-on-grade bearing on medium dense or
more competent native soil or on structural fill (placed on medium dense or more competent soil)
compacted to at least 95 percent of its modified Proctor maximum density. Care should be taken
to compact any localized backfills, such as footing or utility excavations, to the same degree as
that specified for structural fill.
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We recommend that a capillary break be placed beneath slabs. A 4-inch-thick(minimum) layer
of washed pea gravel placed atop floor subgrades, as shown in Figure 10, is recommended to
provide this break. The capillary break should be hydraulically connected to perimeter footing
drains down-slope. As illustrated in Figure 10,the use of 2-inch-diameter weep holes is one
method for providing a hydraulic connection. A vapor barrier consisting of a plastic sheet should
be placed directly over the pea gravel.
6.8 Lateral Earth Pressures and Retaining Structures
Basement walls (rigid)of the future structures should be designed for an at-rest equivalent fluid
pressure of 55 pounds per cubic foot(pcf), plus 1 pound per cubic foot for each degree of
upward inclination of the back-slope above the wall (this is valid up to 20-degree inclinations;
pressures for inclinations greater than 20 degrees will require further calculations). Cantilevered
retaining walls that are not connected to a structure and can yield at the top an amount equal to
0.001 times the wall height could be designed for an active equivalent fluid pressure of 35 pcf,
plus 1 pound per cubic foot for each degree of upward inclination of the back-slope above the
wall (up to 20 degrees). This active pressure would apply to basement walls that can yield as
indicated above. These pressures assume the walls are drained so that hydrostatic pressures
cannot develop. Recommendations for wall drainage and backfilling are presented on Figure 10.
Lateral forces would be resisted by passive earth pressure against the buried portions of
structures and by friction against the bottom. In our opinion,passive earth pressures in backfill
could be estimated using an equivalent fluid pressure of 280 pounds per cubic foot(pcf) above
the groundwater table (or subdrain) and 140 pcf below the water table (or subdrain). These
values assume that the structures extend at least 24 inches below the lowest adjacent grade, and
that the backfill around the structure is a compacted granular fill. The above values include a
factor-of-safety of 1.5.
We recommend that a coefficient of friction of 0.5 be used between cast-in-place concrete and
soil. An appropriate factor-of-safety should be used to calculate the resistance to sliding at the
base of footings.
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We recommend that a capillary break be placed beneath slabs. A 4-inch-thick(minimum) layer
of washed pea gravel placed atop floor subgrades, as shown in Figure 10, is recommended to
provide this break. The capillary break should be hydraulically connected to perimeter footing
drains down-slope. As illustrated in Figure 10,the use of 2-inch-diameter weep holes is one
method for providing a hydraulic connection. A vapor barrier consisting of a plastic sheet should
be placed directly over the pea gravel.
6.8 Lateral Earth Pressures and Retaining Structures
Basement walls (rigid)of the future structures should be designed for an at-rest equivalent fluid
pressure of 55 pounds per cubic foot(pcf), plus 1 pound per cubic foot for each degree of
upward inclination of the back-slope above the wall (this is valid up to 20-degree inclinations;
pressures for inclinations greater than 20 degrees will require further calculations). Cantilevered
retaining walls that are not connected to a structure and can yield at the top an amount equal to
0.001 times the wall height could be designed for an active equivalent fluid pressure of 35 pcf,
plus 1 pound per cubic foot for each degree of upward inclination of the back-slope above the
wall (up to 20 degrees). This active pressure would apply to basement walls that can yield as
indicated above. These pressures assume the walls are drained so that hydrostatic pressures
cannot develop. Recommendations for wall drainage and backfilling are presented on Figure 10.
Lateral forces would be resisted by passive earth pressure against the buried portions of
structures and by friction against the bottom. In our opinion, passive earth pressures in backfill
could be estimated using an equivalent fluid pressure of 280 pounds per cubic foot(pcf) above
the groundwater table (or subdrain) and 140 pcf below the water table (or subdrain). These
values assume that the structures extend at least 24 inches below the lowest adjacent grade, and
that the backfill around the structure is a compacted granular fill. The above values include a
factor-of-safety of 1.5.
We recommend that a coefficient of friction of 0.5 be used between cast-in-place concrete and
soil. An appropriate factor-of-safety should be used to calculate the resistance to sliding at the
base of footings.
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6.9 Erosion Control
Long-term erosion control can be achieved through adequate control and discharge of surface
and subsurface drainage. Following the drainage recommendations contained in the previous
section of this report will mitigate potential long-term erosion. Revegetating cut and fill slopes
with grasses will also provide long-term erosion control. An appropriate grass seed mixture for
this area includes:
Red fescue 40%
Colonial bentgrass 10%
Perennial ryegrass 25%
Orchard grass 15%
White Dutch clover 10%
Other seed mixtures may also be appropriate. For slopes of 2H:1 V or greater, hydroseeding is
recommended. An appropriate hydro-seed mixture on a per acre basis may include:
100 pounds of grass seed
2,000 pounds of wood fiber mulch
250 pounds of 12-24-24 fertilizer
40 gallons of liquid soil bonding agent
If the application is done in summer add:
80 pounds moisture retention agent
500 pounds extra of wood fiber mulch (2,500 pound total)
Summer applications must be irrigated. Seeding should be accomplished by September 15 to
reduce erosion potential for the following rainy season;however, some erosion is possible until
vegetation is well established.
In our opinion,erosion at the site during construction can be minimized by implementing the
recommendations in the Wet Weather Earthwork section, and can be controlled through the
judicious use of fabric silt curtains and/or straw bales and temporary sedimentation ponds.
Temporary erosion control should be the responsibility of the contractor since he/she is also
responsible for the excavation, ditching, sumps, etc.
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7.0 ADDITIONAL CONSIDERATION-TEST PIT EXCAVATIONS
Test pit excavations were loosely backfilled with the excavated material. If such a test pit is
located in a proposed building or pavement area,the loose material should be removed and
replaced with appropriately compacted structural fill. Alternatively,the excavation could be
structurally bridged.
8.0 LIMITATIONS
The conclusions and recommendations presented in this report are based on site conditions as
they presently exist and assume that the explorations are representative of the subsurface
conditions throughout the site; i.e., the subsurface conditions are not significantly different than
those encountered in the test pits and site reconnaissance. If, during construction, subsurface
conditions different from those encountered in the explorations are observed or appear to be
present, we should be advised at once so that we can review those conditions and reconsider our
recommendations where necessary. If there is a substantial lapse of time between submission of
our report and the start of work at the site, we recommend that this report be reviewed to
determine the applicability of the conclusions and recommendations, considering the changed
conditions and/or elapsed time.
This report was prepared for the use of the Owner,Architect, and/or Engineer in the design of
the development and structures. With respect to construction, it should be made available for
information on factual data only and not as a warranty of subsurface conditions, such as those
interpreted from the test pit logs, site reconnaissances, and discussion of subsurface conditions
included in this report.
Unanticipated conditions are commonly encountered and cannot be fully determined merely by
taking soil samples or making explorations. Such unexpected conditions frequently require that
additional expenditures be made to achieve a properly constructed project. Some contingency
fund is recommended to accommodate such potential extra costs.
The scope of our services did not include any environmental assessment for the presence or
absence of hazardous or toxic material in the soil, surface water, groundwater,or air on or below
or around this site. We are able to provide these services and would be happy to discuss these
with you as the need arises.
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Shannon &Wilson has prepared the attached "Important Information About Your Geotechnical
Report," to assist you and others in understanding the use and limitations of our report.
SHANNON & WILSON,INC.
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EXPIRES 5/1/ 43
William J.Perkins,R.P.G. Thomas E. Kirkland, P.E.
Senior Engineering Geologist Vice President
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1-4-96/W7 182-01.RP2/W7I 82-Ikd/dgw
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TABLE 1
GEOTECHNICAL LOGS OF SELECTED SEPTIC TEST PITS
1�1fi �aAepth � WS� malSoi1 d .. .._'
1 1'to 2' Dense,slightly silty,fine SAND
2' to 5' Very dense,clean to slightly silty,sandy GRAVEL with lenses of SAND
6 0' to 2.5' Dense,slightly gravelly,sandy SILT;scattered cobbles
7 1' to+3' Very dense,slightly gravelly,sandy SILT
8 1.5' to+3.5' Very dense,clean to slightly silty,fine SAND
9 2'to 3' Medium dense,clean to slightly silty,gravelly, fine SAND
3' to+5' Very dense,clean to slightly silty,fine SAND
16 1'to 4' Very dense,gravelly sandy SILT;scattered cobbles
4'to+6' Very dense,clean to slightly silty,fine SAND
17 1' to 4' Very dense,gravelly,sandy SILT with beds of fine SAND;scattered cobbles
4'to+11' Very dense,clean to slightly silty,fine SAND
30 2'to 4.5' Very dense,fine SAND
4.5'to+5' Very dense,fine sandy SILT
31 2'to 3' Very dense,slightly silty,fine SAND
3'to 5' Very dense,slightly gravelly,fine SAND,trace of silt
5' to+6' Very dense,sandy GRAVEL;scattered cobbles
37 2'to 4' Dense,slightly silty,gravelly SAND/sandy GRAVEL;scattered cobbles and boulders
4'to+4.5' Very dense,slightly gravelly,sandy SILT
62 1' to 2.5' Medium dense to dense,slightly silty,sandy GRAVEL
2.5'to 4' Dense,fine sandy SILT
4' to+4.5' Very dense,slightly gravelly,silty SAND
64 1.5'to 3' Dense,sandy GRAVEL,trace of silt
3' to+5' Very dense,sandy GRAVEL,trace of silt and cobbles
66 2' to+3.5' Dense,gravelly,silty SAND
68 0.5' to+3' Medium dense,sandy GRAVEL with cobbles
70 0.5' to+3' Medium dense,clean to slightly silty,sandy GRAVEL with cobbles
71 0.5' to 2' Medium dense,slightly silty,sandy GRAVEL
2'to+4' Dense,slightly gravelly SAND
72 0.5'to+3' Medium dense to dense,sandy GRAVEL with lenses of fine to medium SAND
73 0.5'to 3' Medium dense to dense,sandy GRAVEL with cobbles and boulders
3' to+4.5' Very dense,silty,gravelly SAND
74 0.5'to 4' Medium dense to dense,sandy GRAVEL with cobbles and boulders
4'to+4.5' Very dense,silty,gravelly SAND
88 0.5' to+2' Dense,slightly silty,gravelly SAND
89 0.5'to+2' Dense,slightly silty,gravelly SAND
93 2' to+3' Dense,slightly gravelly SAND
94 1' to+3.5' Medium dense to dense,sandy GRAVEL with lenses of fine to medium SAND
95 1.5'to 3' Dense,clean to slightly silty,slightly gravelly SAND
3' to+6' Very dense,slightly gravelly fine SAND
97 1.5' to+3' Dense to very dense,slightly gravelly SAND with lenses of sandy GRAVEL
98 2' to+3' Very dense,slightly gravelly silty SAND
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Jefferson County, WA JEFF CO DEPT OF COMM MISC 40.00
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44684
Pao : 26 of 1
' 011/15/2001 02:52P
Jaf!araan County, WA JEFF CO DEPT OF COMM MISC 40.00
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• Pass: 26 of 34468413
08/15/2001 02:62P
JefIarson County, WA JEFF CO DEPT OF COMM MISC 40.00
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• 4468 1
Paoa: 27 of 33
08/16/2001 02:62P
Jet l•rgon County, WA JEFF CO DEPT OF COMM MISC 40.00
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•
446841
1E1 II 1 III 1111111 P.Q.: 2B of 83
08/1 ti/2001 02.64P
Jefferson County, WA JEFF CO DEPT OF COMM MISC 40.00
Maximum slope behind rockery is 3H
to IV for a horizontal distance equal
8"Compacted Native Soil to the height of the rockery.
(Impervious Surface Layer) 3
11
•
.,,,,,,-
Stable Excavation Slope in
Dense Native Soil
•:•:•:-•::•::• (Contractor's Responsibility)
1 "��• ' ' Openings Chinked
:: : with Quarry Spalls
•
H=8'Max. 4 ` Backfill
�-`•- •::•':'•':••' Clean, well-graded sand&gravel or
alp
•''•'• ' crushed rock,2"max.size,40 to 60%
gravel,less than 5%fines(passing
#200 sieve). Fines shall be non-plastic.
i�':' Compact in 6"lifts with min. of 4
coverages by hand-operated tamper.
� Compact to at least 92%of Modified
` • '''•'•'' Proctor maximum dry density(ASTM
I O-1557--70). Backfill and rock
12"Min. • • ••••• placement should be built up together.
4"Diameter Slotted ABS Pipe
Bedded in washed 3/8"pea gravel(6"
cover around pipe),sloped to drain and
H/3 Min.Width '.I connected by tightline to storm drain
for Base Rock outfall. No fabric around pipe.
All loose to medium dense soil at rockery
foundation should be everexcavated down to
dense or hard soil and replaced with compacted
backfill as described above. The excavation
shall be kept free of water. The prepared
rockery foundation shall be evaluated by a soils
engineer prior to placement of rock.
Not to Scale
MINIMUM WEIGHT OF ROCK Sugar Hill Estates
Chimacum,Washington
Portion of wall below 6 feet, 2400 lb.
("6-man")rock. Portion of wall above
6 feet, 1600 lb.("4-man")rock. TYPICAL ROCKERY DETAIL
January 1996 W-7182-01
SHANNON & WILSON, INC. FIG. 9
Geotechnical and Environmental Consultants
•
11111111 41
P.a.:4468 29 or as
II III 001
Jsff.rson County, WA JEFF CO DEPT OF COMM M0ISC6r40 00 02.62P
Sloped to Drain �`�
Away from i�Wall
Structure
Pavement or 10"to 15" Drainage Sand
Impervious Soil
8�
o ° Gravel or Washed
° Pea Gravel
Backfill Meeting Gradation
Requirements for Structural Fill 18" ° o. —Damp Proofing
(See Note 2) Min.'s'% ° //
Weep Holes
Excavation Slope �0 (See Note 1) Vapor Barrier
Contractor's r
Responsibility o Floor Slab 1 1
6"Min. Cover of Pea Gravel __ ° o ' 0
(6"Min.on Sides of Pipe) • OF e°� ° °
Subdrain Pipe 2"to 4' 4"Min
Washed
Pea Gravel
Not to Scale
MATERIALS NOTES
Drainage Sand&Gravel with 1. Drainage gravel beneath floor slab should be
the Following Specifications: hydraulically connected to subdrain pipe. Use of 2"
diameter weep holes as shown is one applicable method.
Passing 2. Imported structural fill should consist of well-graded
Sieve Size by Weight 9
granular soil with no more than 5%fines(by weight
1-1/2" 100 based on minus 3/4"portion)passing No.200 sieve(by
3/4" 90 to 100 wet sieving)with no plastic fines.
1/4" 75 to 100 3. Backfill within 18"of wall should be compacted with
No.8 65 to 92 hand-operated equipment. Heavy equipment should not
No.30 20 to 65 be used for backfill,as such equipment operated near
No.50 5 to 20 the wall could increase lateral earth pressures and
No. 100 0 to 2 possibly damage the wall.
(by wet sieving) (non-plastic)
4. All backfill should be placed in layers not exceeding 4"
loose thickness and densely compacted. Beneath paved
or sidewalk areas,compact to at least 95%modified
Proctor maximum density(ASTM:D1557-70 Method C
or D). Otherwise compact to 92%minimum.
SUBDRAIN PIPE NOTES
4"minimum diameter perforated or slotted pipe; Sugar Hill Estates
tight joints; sloped to drain(6"/100'min.slope);
provide clean-outs. Chimacum, Washington
Perforated pipe holes(3/16"to 3/8"dia.)to be in
lower half of the pipe with lower quarter segment SUBDRAINAGE & BACKFILLING
unperforated for water flow.
Slotted pipe to have 1/8"maximum width slots. January 1996 W-7182-01
SHANNON&WILSON, INC.
Geotechnical and Environmental Consultants FIG. 10
0
1111111111111111111111111 446841
Non: 30 of 33
011/16/2001 02:02P
Jefferson County, WA JEFF CO DEPT OF COMM MISC 40.00
APPENDIX
IMPORTANT INFORMATION ABOUT YOUR GEOTECHNICAL REPORT
W-7182-01
446841
•
Pao1: 31 of 33
0ti/1612001 02:t32P
Jefferson County, WA JEFF CO DEPT OF COMM MSC 40.00
SHANNON &WILSON, INC. Attachment to and part of Report W-7182-01
- Geotechnical and Environmental Consultants
IMF Date: July 30,2001
To: Mr.Bill Lowry
Chimacum,Washington
Important Information About Your GeotechnicaUEnvironmental Report
CONSULTING SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES AND FOR SPECIFIC CLIENTS.
Consultants prepare reports to meet the specific needs of specific individuals. A report prepared for a civil engineer may
not be adequate for a construction contractor or even another civil engineer. Unless indicated otherwise,your consultant
prepared your report expressly for you and expressly for the purposes you indicated. No one other than you should apply
this report for its intended purpose without first conferring with the consultant. No party should apply this report for any
purpose other than that originally contemplated without first conferring with the consultant.
THE CONSULTANT'S REPORT IS BASED ON PROJECT-SPECIFIC FACTORS.
A geotechnical/environmental report is based on a subsurface exploration plan designed to consider a unique set of
project-specific factors. Depending on the project,these may include: the general nature of the structure and property
involved; its size and configuration; its historical use and practice; the location of the structure on the site and its
orientation;other improvements such as access roads,parking lots,and underground utilities;and the additional risk
created by scope-of-service limitations imposed by the client. To help avoid costly problems,ask the consultant to
evaluate how any factors that change subsequent to the date of the report may affect the recommendations. Unless your
consultant indicates otherwise,your report should not be used:(1)when the nature of the proposed project is changed
(for example,if an office building will be erected instead of a parking garage,or if a refrigerated warehouse will be built
instead of an unrefrigerated one, or chemicals are discovered on or near the site); (2) when the size, elevation, or
configuration of the proposed project is altered;(3)when the location or orientation of the proposed project is modified;
(4) when there is a change of ownership; or (5) for application to an adjacent site. Consultants cannot accept
responsibility for problems that may occur if they are not consulted after factors which were considered in the
development of the report have changed.
SUBSURFACE CONDITIONS CAN CHANGE.
Subsurface conditions may be affected as a result of natural processes or human activity. Because a
geotechnical/environmental report is based on conditions that existed at the time of subsurface exploration,construction
decisions should not be based on a report whose adequacy may have been affected by time. Ask the consultant to advise
if additional tests are desirable before construction starts; for example, groundwater conditions commonly vary
seasonally.
Construction operations at or adjacent to the site and natural events such as floods, earthquakes, or groundwater
fluctuations may also affect subsurface conditions and,thus,the continuing adequacy of a geotechnical/environmental
report. The consultant should be kept apprised of any such events,and should be consulted to determine if additional
tests are necessary.
Page 1 of 3 1/2001
44684
•
1111111111 1 Papa; 32 of 33
Jot?orlon County, WA JEFF CO DEPT OF COMM M SC6/200 40.90 2'62P
MOST RECOMMENDATIONS ARE PROFESSIONAL JUDGMENTS.
Site exploration and testing identifies actual surface and subsurface conditions only at those points where samples are
taken. The data were extrapolated by your consultant,who then applied judgment to render an opinion about overall
subsurface conditions. The actual interface between materials may be far more gradual or abrupt than your report
indicates. Actual conditions in areas not sampled may differ from those predicted in your report. While nothing can be
done to prevent such situations,you and your consultant can work together to help reduce their impacts. Retaining your
consultant to observe subsurface construction operations can be particularly beneficial in this respect.
A REPORT'S CONCLUSIONS ARE PRELIMINARY.
The conclusions contained in your consultant's report are preliminary because they must be based on the assumption that
conditions revealed through selective exploratory sampling are indicative of actual conditions throughout a site. Actual
subsurface conditions can be discerned only during earthwork;therefore,you should retain your consultant to observe
actual conditions and to provide conclusions. Only the consultant who prepared the report is fully familiar with the
background information needed to determine whether or not the report's recommendations based on those conclusions
are valid and whether or not the contractor is abiding by applicable recommendations. The consultant who developed
your report cannot assume responsibility or liability for the adequacy of the report's recommendations if another party
is retained to observe construction.
THE CONSULTANT'S REPORT IS SUBJECT TO MISINTERPRETATION.
Costly problems can occur when other design professionals develop their plans based on misinterpretation of a
geotechnical/environmental report. To help avoid these problems,the consultant should be retained to work with other
project design professionals to explain relevant geotechnical,geological,hydrogeological,and environmental findings,
and to review the adequacy of their plans and specifications relative to these issues.
BORING LOGS AND/OR MONITORING WELL DATA SHOULD NOT BE SEPARATED FROM THE
REPORT.
Final boring logs developed by the consultant are based upon interpretation of field logs(assembled by site personnel),
field test results,and laboratory and/or office evaluation of field samples and data. Only final boring logs and data are
customarily included in geotechnical/environmental reports. These final logs should not,under any circumstances,be
redrawn for inclusion in architectural or other design drawings,because drafters may commit errors or omissions in the
transfer process.
To reduce the likelihood of boring log or monitoring well misinterpretation,contractors should be given ready access
to the complete geotechnical engineering/environrnental report prepared or authorized for their use. If access is provided
only to the report prepared for you,you should advise contractors of the report's limitations,assuming that a contractor
was not one of the specific persons for whom the report was prepared,and that developing construction cost estimates
was not one of the specific purposes for which it was prepared. While a contractor may gain important knowledge from
a report prepared for another party, the contractor should discuss the report with your consultant and perform the
additional or alternative work believed necessary to obtain the data specifically appropriate for construction cost
estimating purposes. Some clients hold the mistaken impression that simply disclaiming responsibility for the accuracy
of subsurface information always insulates them from attendant liability. Providing the best available information to
contractors helps prevent costly construction problems and the adversarial attitudes that aggravate them to a
disproportionate scale.
READ RESPONSIBILITY CLAUSES CLOSELY.
Page 2 of 3 1/2001
Pao.; 73 of 34468413
00f16f2001 02,f32P
Jsff.r.on County, WA JEFF CO DEPT OF COMM MISC 40.00
Because geotechnical/environmental engineering is based extensively on judgment and opinion,it is far less exact than
other design disciplines.This situation has resulted in wholly unwarranted claims being lodged against consultants. To
help prevent this problem,consultants have developed a number of clauses for use in their contracts,reports and other
documents. These responsibility clauses are not exculpatory clauses designed to transfer the consultant's liabilities to
other parties;rather,they are definitive clauses that identify where the consultant's responsibilities begin and end. Their
use helps all parties involved recognize their individual responsibilities and take appropriate action. Some of these
definitive clauses are likely to appear in your report,and you are encouraged to read them closely. Your consultant will
be pleased to give full and frank answers to your questions.
The preceding paragraphs are based on information provided by the
ASFE/Association of Engineering Firms Practicing in the Geosciences,Silver Spring,Maryland
Page 3 of 3 1/2001
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respect to its correctness or validity. Data contained in this map is limited by the method and accuracy of its
ollection. Mon Feb 14 12:04:47 2005
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FOR INFORMATIONAL PURPOSES ONLY-
Jefferson County does not attest to the accuracy of the data contained herein and makes no warranty with
respect to its correctness or validity. Data contained in this map is limited by the method and accuracy of its
collection. Mon Feb 14 12:05:56 2005
http://gisserver/servlet/com.esri.esrimap.Esrimap?ServiceName=ovmap&ClientVersion=4.0&Form=True... 2/14/2005