HomeMy WebLinkAboutBLD2005-00304 Geotechnical Report • Getesources, LLC
Ph. 253-896-1011 5007 Pacific Hwy. E., Suite 20
Fx. 253-896-2633 — Fife, Washignton 98424
MAY 1 1 2005antary 17, 2005
Mr. Terry Ellingson
Ms. Elaine Morgan
5145 NW El Camino Boulevard
Bremerton, Washington 98312
Geotechnical Evaluation &
Design Report
Lot 8, Division 5, Bridgehaven
Thorndyke Road
Jefferson County, Washington
Job No. Ellingson.Thorndyke.01 RG
INTRODUCTION and SCOPE
This geotechnical report presents the results of our geotechnical evaluation of the above
referenced lot to provide geotechnical design criteria and recommendations for the proposed single-family
residential development at the above referenced site. The project site is located at Lot 8, Division 5 of
Bridgehaven, in unincorporated Jefferson County, Washington. The site is generally situated in the South
Point area of Jefferson County, along Hood Canal, east of the intersection Finch Lane and Thorndyke
Road. The location of the site is shown on the Vicinity Map, Figure 1.
Our understanding of the project is based on our discussions with you, our site observations and
test pit, our experience in the area and our review of the data provided. We understand that the site
development will consist of a single-family residence on the lot. Development at the site will include the
typical associated utilities and driveway. Based on our site observations and discussions with you, grading
at the site will be associated with construction of the driveway and excavation of the foundation/driveway
areas. The general layout of the site is illustrated in the Site Plan, Figure 2.
The proposed residential structure will be situated to take advantage of the grade changes at the
site, which are well suited to conventional daylight basement construction. The site is bounded by
established residences to the north and south, with Thorndyke Road forming the western property margin.
The site consists of a relatively level upland area where the residence is proposed. The upland area
abuts a steep slope area which descends to the east. Access to the proposed house site will be from
Thorndyke Road to a proposed garage which will be located below the proposed residence on the north
side of the residence.
Slopes in the eastern portion of the site exceed 30 percent, with maximum relief well in excess of
10 vertical feet. The purpose of our services is to evaluate the site soils and groundwater conditions as a
basis for assessing the critical areas, potential landslide, seismic and erosion hazards, at the site, and to
develop geotechnical recommendations and design criteria for the proposed site development.
Specifically, our scope of services for this project includes the following:
1. Review the available surface and subsurface soil and ground water information, including the
existing geotechnical and perc-hole data, Washington DOE maps and Jefferson County Soil
Conservation Service documents.
2. Visit the site and conduct a geologic reconnaissance to assess the site's slope, soil and ground
water conditions.
3. Evaluate the shallow subsurface conditions at the site by monitoring the excavation of test pits at
the building site.
4. Provide geotechnical recommendations for site grading including site preparation, subgrade
preparation, fill placement criteria, suitability of on-site soils for use as structural fill, temporary and
permanent cut and fill slopes, drainage and erosion control measures.
Ellingson/Morgan-Thorndyke • •
January 17, 2005
Page 2
5. Provide recommendations and design criteria for foundation and floor slab support, including
allowable bearing capacity, subgrade modulus. lateral resistance values and estimates of
settlement.
6. Provide recommendations and design criteria for the design of conventional subgrade/retaining
(basement)walls, including backfill and drainage requirements, lateral design loads, and lateral
resistance values.
SITE CONDITIONS
SURFACE& GEOLOGIC CONDITIONS
The site is located in the South Point area of Jefferson County. The lot is an irregularly shaped
parcel that measures 88-feet along Thorndyke Road by 230 to 244-feet east to west. The lot width tapers
to the east, and is only 52-feet wide at the eastern property margin. The steeper slopes in the eastern
portion of the site appear to be related to steep soils that formed on canyon slopes and ocean bluffs. The
upland materials are deposits that likely formed in outwash and are somewhat excessively drained. The
relative topography of the site area is shown on the Site Plan, Figure 2. Areas with slopes of 15 to 29
percent, and the local slope area in excess of 30 percent are illustrated on Figure 2.
The upland portion of the site is currently vegetated with scattered timber and locally dense brush
undergrowth. The trees consist of a mix of evergreen and madrona. No evidence of erosion was
observed at the site at the time of our site observations, particularly where the vegetation is established.
The slope area below the proposed home site is densely covered with low brush. No shallow groundwater
seepage and/or surface flow was observed in the portion of the site where the home site is proposed.
Based on our data review (available geologic and geotechnical data), our geologic
reconnaissance of the site area, our test pit excavations, review of perc test hole data provided to us, and
our experience in the area, the shallow soils at the site likely consist of outwash sand with a trace gravel.
These soils likely were deposited over glacially consolidated deposits (till or hardpan and outwash
material) and interglacial sediments.
Recessional outwash soils were deposited as the glacial ice retreated and are typically medium
dense. These surficial soils were deposited subsequent to the Fraser Glaciation, some 12,000 to 15,000
years ago. Below the recessional deposits, glacially consolidated soils are typically present. Vashon
glacial till was deposited at the base of the advancing glacial ice and is in a very dense condition where
undisturbed. Advance outwash material was deposited by meltwater from the advancing glacial ice, and
subsequently over-ridden by the glacial ice. The advance outwash soils are likewise in a dense condition,
except where disturbed by weathering or previous grading activity. No significant intersecting geologic
contacts were observed in our test pit excavations or the open perc-holes at the site. Shallow
groundwater and surface seepage was not observed in the test holes advanced in the building or septic
drainfield areas. No evidence of surficial erosion was observed at the site at the time of our site visits,
particularly where vegetation is well established.
SITE SOILS
A review of the Soil Survey of Jefferson County(Soil Conservation Survey) indicates that the site
soils consist of Everett gravelly sandy loam (0 to 15 per cent) in the upland area abutting Cassolary sandy
loam (30 to 50 per cent). The Everett soils are generally derived from sandy glacial outwash soils and
consist of somewhat excessively well-drained sands. Based on the SCS data, the Everett soils have a
slight to moderate erosion hazard. The steeper Cassolary deposits have a severe erosion hazard.
SUBSURFACE EXPLORATIONS
Subsurface conditions at the site were evaluated by observing the exposed soils in perc holes
excavated on site and observing 2 test pit excavated in the proposed building area, reviewing the available
geologic and geotechnical data for the site area and our site reconnaissance. The perc holes were
excavated in 4-locations west of the home in the proposed location of the on-site septic drainfield. Two
additional test pit was excavated near the proposed building area. The perc-holes extended to a
maximum of about 4-feet below ground surface (bgs), while the test pits were extended to 6.5 to 7-feet
bgs. Uniform and favorable soils were disclosed at all locations explored. Site soils generally consist of a
layer of topsoil above moist red-brown grading to light brown fine to medium sand. The light brown sand
Ellingson/Morgan-Thorndyke •
January 17, 2005
Page 3
included a trace of gravel.
No groundwater was encountered within the depths explored, and the sidewalls of the test pit
were stable. Based on the consistent nature of the soil conditions encountered in the perc holes and test
pit, and our previous experience in the area, it is our opinion that no additional excavations or borings are
required to characterize the site soils or evaluate their stability.
The outwash soils were in a medium dense to dense condition, except where disturbed by
surficial weathering. No ground water seepage was observed in our explorations. Groundwater conditions
may vary with changes in precipitation, changes in site utilization, and other factors.
CONCLUSIONS
GENERAL
Based on the results of our site reconnaissance. data review, subsurface explorations and our
experience in the area, it is our opinion that the site is suitable for the proposed single-family residential
development. The construction of the daylight basement structure would provide additional stability in the
building areas with sloping surfaces. Grading at the site will generally occur in the western and
southwestern portions of the site associated with excavations for foundations and the driveway. Based on
the soils encountered and our understanding of the proposed site development, conventional earthwork
and foundation support is feasible at the site. Conventional foundation support may be utilized for the
structure. Pertinent conclusions and geotechnical recommendations regarding the design and
construction of the proposed development are presented below.
SEISMIC -LIQUEFACTION
According to the Seismic Zone Map of the United States contained in Figure 16-2 of the 1997
UBC (Uniform Building Code), the project site is located within Seismic Risk Zone 3. Based on the
subsurface conditions observed at the site, we interpret the site conditions to correspond to a seismic Soil
Profile type SD, for Dense Soil, as defined by Table 16-J (UBC), or as Site Class "D" in the 2003 IBC/IRC
building code documents, in accordance with Table 1615.1.1. This is based on the inferred range of SPT
(Standard Penetration Test) blow counts relative to test pit excavation progress and probing with a %-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 not
susceptible to liquefaction. The near-surface soils below the upper weathered soils are generally in a
medium dense to dense condition, and are likely underlain by very dense glacially overridden soils, and
the static water table is located well below the site. Shaking of the already medium dense soil is not apt to
produce a denser configuration and subsequently excess pore water pressures are not likely to be
produced. Collection of the shallow perched groundwater in the south and west central portions of the site
will improve overall stability at the site.
LANDSLIDE HAZARD
Classification
Portions of the project site are located in an area mapped as"Unstable" by the Washington State
Department of Ecology in the Coastal Zone Atlas. In addition, based on the proximity of the steep slope to
the east, and previous repeated landslide activity associated with retaining wall construction on a nearby
property, we understand that Jefferson County has designated the project vicinity as a landslide hazard
overlay area. The writer was involved in the forensic evaluation of the previous landslide activity which
occurred several properties north of the subject property. Based on that work, the landslide activity at the
nearby site was triggered by the construction of a bin wall which was located below the residence and on
the steep descending slope below the home. That localized slide area was repaired by the construction of
a series of short timber walls extending full height up the slope which restored the slope and is intended to
protect against further erosion and loss of ground.
The soils in the flatter portion of the site where the residence will be constructed are mapped by
the SCS (Jefferson County Soil Conservation Survey) as Everett gravelly sandy loam. The limitations for
home site relate to the moderately steep to steep soils. Based on the above, we conclude that the site
does the meet the technical criteria for a landslide hazard area.
Ellingson/Morgan-Thorndyke • .
January 17, 2005
Page 4
EROSION HAZARD
The building site on the subject lot is located in an area mapped by the Soil Conservation Service
as Everett gravelly sandy loam. The erosion hazard for these soils is slight to moderate. However, the
stepper Cassolary soils comprising the slope below the home are rated as a severe erosion hazard.
It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed
residential development. The proposed new home would be set back from the edge of the steep slope by an
appropriate buffer(greater than 30-feet). Removal of natural vegetation should be minimized and limited to the
active construction areas, except for the removal of hazard trees in proximity to the break in slope. Temporary
and permanent erosion control measures should be installed and maintained during construction 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 berms and swales with check dams to
channel surface water runoff, ground cover/protection in exposed areas and silt fences. Graded areas
should be shaped to avoid concentrations of runoff onto cut or fill slopes, natural slopes or other erosion-
sensitive areas. Temporary ground cover/protection such as jute or excelsior matting, wood chips or plastic
sheeting should be used until permanent erosion protection is established.As previously discussed,
weathering and erosion are natural processes that affect steep slope areas. As noted, no evidence of surficial
raveling or sloughing was observed on site. To manage and reduce the potential risk for these natural
processes, we recommend the following:
• No drainage of concentrated surface water or significant sheet flow onto or near the slope area.
• Replant/vegetate disturbed slope areas outside of the building limits with deeply rooted low vegetation.
• Install erosion control measures(as described above)as soon as practical in the disturbed building area.
We expect this will include conventional landscaping and erosion protection.
Building Setback
Jefferson County requires a building setback and buffer area from all landslide and erosion hazard areas.
The buffer distance is calculated based on the vertical height of the slope. Alternatively, a structural setback
may be recommended by a licensed geotechnical engineer. Vegetation in the buffer may be enhanced, if
approved or required. Clearing, grading and filling within the setback area is allowed if it can be demonstrated
that the buffer vegetation will not be adversely impacted, or if the impacts can be mitigated.
Based on our geotechnical evaluation of the site, we recommend a Structural Setback of 30 feet
where footings will be founded in the medium dense native soils. The Structural Setback may be measured
horizontally from the bottom of the footing to the face of the slope where slopes are 30 percent or steeper, as
described in the"Buffer Modification"section of this report.
Buffer Modification
Where necessary, the Structural Setback may be measured from the bottom of the footing to the
face of the steep slope, in accordance with UBC/IBC. Where the Setback Modification is utilized, the
foundation elements should be extended vertically to meet the recommended setback criteria. This
modification is based on the foundation elements extending to and being founded in medium dense to dense
soils. Maintaining the prescribed setback in this manner provides the conventional 2 to 1 bearing prism. A
schematic section is provided as Figure 6.
Roadways and driveways are exempt from the Building Setback criteria. Conventional earthwork
guidelines should be utilized with the recommended geotechnical design criteria for cuts and fills in the
roadway and driveway areas, as described in the"Earthwork Section"of this report.
As previously discussed, weathering, erosion and the resulting surficial sloughing and shallow
landsliding are natural processes that affect steep slope areas. As noted, localized evidence of surficial
raveling and riling were not observed in the steeper portions of the site owing to the dense ground cover. To
mitigate and reduce the potential for these natural processes to become exacerbated, we recommend the
following: No drainage of concentrated surface water or significant sheet flow onto or near the slope area.
Drainage from the roof and driveway area should be collected and tightlined to the site's on-site infiltration
system, or sheet flowed to densely vegetated portions of the site.
Ellingson/Morgan-Thorndyke
•
January 17, 2005
Page 5
• No filling within the setback zone unless retained by engineered retaining walls or constructed as a
monitored and engineered fill.
• No percolation of surface water within 30 feet of the top of the steep slope unless the seepage rate is
controlled to a slow seep(similar to septic systems).
EARTHWORK
Site Preparation
Grading at the site is expected to be limited to and generally associated with construction of the
driveway and excavation for the garage and residence. Depending on site grades, we anticipate the
garage floor will be constructed below existing site grades, requiring the construction of
retaining/basement walls around the perimeter of the garage. The house would be constructed one story
above the garage elevation. All areas to be graded/excavated should be cleared of deleterious matter
including any existing structures, foundations, abandoned utility lines, debris and vegetation. Graded
areas should be stripped of any forest duff and organic-laden soils.
Based on our explorations, we estimate that stripping on the order of 5 to 8 inches will be
necessary to remove the root zone and surficial soils containing significant organic materials. Areas with
deeper, unsuitable organics should be expected in the vicinity of depressions, steep slopes or heavy
vegetation. Stripping depths of up to 2.5 feet may occur in these areas. These organic materials may be
stockpiled and later used for erosion control and landscaping/revegetation. Materials that cannot be used
for landscaping or erosion control should be removed from the project site.
Existing areas of uncontrolled fill material, if present, below proposed final grades of the future
home site or project improvement areas, should be removed and recompacted in accordance with the
recommendations provided in this report.
Where placement of fill material is required, the exposed subgrade areas should be compacted to
a firm and unyielding surface prior to placement of any fill. We recommend that trees be removed by
overturning in fill areas so that a majority of the roots are removed. Excavations for tree stump removal
should be backfilled with structural fill compacted to the densities described in the "Structural Fill"
section of this report.
Any soft, loose or otherwise unsuitable areas delineated during proofrolling or probing should be
recompacted, if practical, or overexcavated and replaced with structural fill, based on the
recommendations of our site representative.
Structural Fill
All fill material/trench backfill 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 95 percent of MDD (maximum dry density as determined in accordance
with ASTM D-1557).
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. We recommend that our representative be present during site grading activities to observe
the work and perform field density tests.
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 US 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 use of well-graded sand and gravel with less than
5 percent(by weight) passing the US No. 200 sieve based on that fraction passing the 3/4-inch sieve. If
prolonged dry weather prevails during the earthwork and foundation installation phase of construction, a
somewhat higher(up to 10 to 12 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
Ellingson/Morgan-Thorndyke • •
January 17,2005
Page 6
Suitability of On-Site Materials as Fill
During dry weather construction, any nonorganic on-site soil may be considered for use as
structural fill, provided it meets the criteria described above in the structural fill section and can be
compacted as recommended. If the material is over-optimum moisture content when excavated, it will be
necessary to aerate or dry the soil prior to placement as structural fill. Many of the soils encountered in
our test pits appeared near optimum moisture content.
The workability of material for use as structural fill will depend on the gradation and moisture
content of the soil. As the amount of fines increases, soil becomes increasingly more sensitive to small
changes in moisture content and adequate compaction becomes more difficult or impossible to achieve.
The soils at the site generally consist of fine to medium sand with trace gravel. These soils are
comparable to Class A"pit run" material and will be suitable for use as structural fill provided the moisture
content is appropriate. Any organic the soils should be stockpiled and treated in a similar manner as the
topsoil strippings.
All fill material in the building and driveway areas should be placed as described in the
"Structural Fill" section of this report and compacted to at least 95 percent of the MDD. If fill material is
imported to the site for wet weather construction, we recommend that it be a sand and gravel mixture such
as high quality pit run with less than 5 percent fines.
CUT AND FILL SLOPES
All job site safety issues and precautions are the responsibility of the contractor providing
services/work. Temporary cut slopes will likely be necessary during grading operations or utility
installation. As a general guide, temporary slopes of 1.5 to 1 (horizontal to vertical) or flatter may be used
for temporary cuts for the site soils in a medium dense condition. Should ground water seepage be
encountered, such as in proximity to the drainage swale, flatter temporary slopes may be required.
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.
We recommend a maximum slope of 2 to 1 for permanent cut and fill slopes in areas of medium
dense sand and gravel. Where 2 to 1 slopes are not feasible in these soils, retaining structures should be
considered. Where retaining structures are greater than 4-feet in height(bottom of footing to top of
structure) or have slopes of greater than 15 percent above them, they should be engineered. In areas of
dense to very dense undisturbed glacial till, permanent cut slopes of 1.5 to 1 may be constructed. It
should be recognized that slopes of this nature do ravel and require occasional maintenance. Where
raveling or maintenance is unacceptable, we recommend that flatter slopes or retaining systems be
considered.
Fill placed on slopes that are steeper than 5 to 1 should be "keyed" into the undisturbed native
soils by cutting a series of horizontal benches. The benches should be 1'/2 times the width of equipment
used for grading and a maximum of 3 feet in height. Subsurface drainage may be required in seepage
areas. Surface drainage should be directed away from all slope faces. Some minor raveling may occur
with time. All disturbed areas should be vegetated or otherwise protected as soon as practical to facilitate
the development of a protective vegetative layer or establishment of a permanent erosion protection.
FOUNDATION SUPPORT
We recommend that spread footings for any residence be founded on medium dense or denser
native soils or on structural fill that extends to suitable native soils. The soil at the base of the excavations
should be disturbed as little as possible. All loose, soft or unsuitable material should be removed or
recompacted, as appropriate. A representative from our firm should observe the foundation excavations
to determine if suitable bearing surfaces have been prepared, particularly in the areas where the
foundation will be situated in fill material. We recommend that daylight basement structures be
considered for the site. All exterior footing elements should be embedded at least 18 inches below grade
for frost protection. Where foundation elements are located near slopes of 15 percent of more, 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 16 inches for
continuous wall footings. Footings founded as described above can be designed using an allowable soil
. Ellingson/Morgan-Thorndyke .
January 17, 2005
Page 7
bearing capacity of 2,000 psf(pounds per square foot) for combined dead and long-term live loads. 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 base of footings and floor slabs and as passive
pressure on the sides of footings. We recommend that an allowable coefficient of friction of 0.35 be used
to calculate friction between the concrete and the underlying soil. Passive pressure may be determined
using an allowable equivalent fluid density of 300 pcf(pounds per cubic foot). Factors of safety have been
applied to these values.
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 1/2 inch or less. Most of the settlements should occur essentially as loads are being applied.
However, disturbance of the foundation subgrade during construction could result in larger settlements
than predicted.
FLOOR SLAB SUPPORT
Slabs-on-grade (garage or floor) should be supported on medium dense or denser 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 4-inch thickness of coarse sand and/or gravel containing
less than 3 percent fines. The drainage material should be placed in one lift and compacted to an
unyielding condition.
A synthetic vapor barrier is recommended for the control of moisture migration through the
slab, in particular 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.
A subgrade modulus of 400 kcf(kips per cubic foot) may be used for floor slab design. We
estimate that settlement of the floor slabs designed and constructed as recommended, will be 1/2 inch or
less over a span of 50 feet.
SUBGRADE AND RETAINING WALLS
The lateral pressures acting on subgrade and retaining (basement) 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 walls are backfilled with granular well-drained soil, the design active pressure
may be taken as 35 pcf(pounds per cubic foot)equivalent fluid density. This design value assumes a
level backslope and drained conditions as described below. The design for active pressure assumes the
walls can yield 0.001 times the wall height. Stiffer walls, or walls restrained from movement by
diaphragms or floors, should be designed to resist at-rest pressures of 50 pcf.
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 such 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 base of footings and as passive pressure on the
sides of footings and the buried portion of the wall. We recommend that an allowable coefficient of friction
of 0.35 be used to calculate friction between the concrete and the underlying soil. Passive pressure may
be determined using an allowable equivalent fluid density of 300 pcf. Factors of safety have been applied
to these values.
Ellingson/Morgan-Thorndyke • •
January 17, 2005
Page 8
PAVEMENT or DRIVEWAY SUBGRADE
We recommend that pavement and/or driveway slab subgrades be prepared in accordance with
the previously described site preparation and structural fill recommendations. The upper 2 feet of
roadway subgrade should have a density of at least 95 percent of the MDD (ASTM D-1577).
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 dispersed into vegetated areas, or conveyed to the site's stormwater
infiltration system. We recommend that conventional roof and footing drains be installed for all structures.
Drains should be provided behind all retaining walls. The roof drain should not be connected to the footing
drain unless an adequate gradient will prevent a surcharge of the footing drain. Collected stormwater should
be directed to the site's stormwater system. The system location has yet to be determined. Ideally, storm
water should be tightlined to the base of the hill side. However, that will result in some disturbance to the
sensitive slope area below the proposed home. Alternatively, as discussed earlier, stormwater may be
infiltrated. No drainage of concentrated surface water or significant sheet flow onto or over the slope area
should be allowed. Drainage from the driveway area should be sheet flowed to the adjacent vegetated
portions of the site. No percolation of surface water within 30 feet of the top of the steep slope unless the
seepage rate is controlled to a slow seep(similar to septic systems).
Ellingson/Morgan-Thomdyke 0 •
January 17,2005
Page 9
LIMITATIONS
We have prepared this report for use by Mr. Terry Ellingson and Ms. Elaine Morgan, and
members of their design team, for 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
limited site reconnaissance, and should not be construed as a warranty of the subsurface conditions.
Variations in subsurface conditions are possible between the explorations and may also occur
with time. A contingency for unanticipated conditions should be included in the budget and schedule.
Sufficient monitoring, testing and consultation should be provided by our firm during construction to
confirm that the conditions encountered are consistent with those indicated by the explorations, to provide
recommendations 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 and specifications.
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 type 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.
Within the limitations of scope, schedule and budget, our services have been executed in
accordance with generally accepted practices in this area at the time this report was prepared. No other
conditions, express or implied, should be understood.
Respectfully submitted,
GeoResources, LLC
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5007 Pacific Highway East, Suite 20 Figure 1: Site Vicinity Map
Fife, Washington 98424
Phone: 253-896-1011
Fax: 253-896-2633
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5007 Pacific Highway East, Suite 20 Figure 3: USDA SCS Map
Fife, Washington 98424
Phone: 253-896-1011
Fax: 253-896-2633
• •
SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS GROUP GROUP NAME
SYMBOL
GRAVEL CLEAN GW WELL-GRADED GRAVEL,FINE TO COARSE GRAVEL
GRAVEL
COARSE GP POORLY-GRADED GRAVEL
GRAINED More than 50%
SOILS Of Coarse Fraction GRAVEL GM SILTY GRAVEL
Retained on WITH FINES
No.4 Sieve GC CLAYEY GRAVEL
SAND CLEAN SAND SW WELL-GRADED SAND, FINE TO COARSE SAND
More than 50%
Retained on
No.200 Sieve SP POORLY-GRADED SAND
More than 50%
Of Coarse Fraction SAND SM SILTY SAND
Passes WITH FINES
No.4 Sieve SC CLAYEY SAND
SILT AND CLAY INORGANIC ML SILT
FINE
GRAINED CL CLAY
SOILS Liquid Limit
Less than 50 ORGANIC OL ORGANIC SILT,ORGANIC CLAY
SILT AND CLAY INORGANIC MH SILT OF HIGH PLASTICITY, ELASTIC SILT
More than 50%
Passes CH CLAY OF HIGH PLASTICITY, FAT CLAY
No.200 Sieve
Liquid Limit
50 or more ORGANIC OH ORGANIC CLAY,ORGANIC SILT
HIGHLY ORGANIC SOILS PT PEAT
NOTES: SOIL MOISTURE MODIFIERS:
1. Field classification is based on visual examination of soil Dry- Absence of moisture,dry to the touch
in general accordance with ASTM D2488-90.
Moist- Damp, but no visible water
2. Soil classification using laboratory tests is based on
ASTM D2487-90. Wet- Visible free water or saturated, usually soil is
obtained from below water table
3. Description of soil density or consistency are based on
interpretation of blow count data,visual appearance of
soils,and or test data.
GeoResources, LLC SOIL CLASSIFICATION SYSTEM
5007 Pacific Hwy. E, Ste 20
Fife, Washington 98424-2648
Ph. 253-896-1011
Fx. 253-896-2633 FIGURE 4
. •
TEST PIT LOGS
MORGAN/ELLINGSON RESIDENTIAL SITE
LOT 8, DIVISION 5 BRIDGEHAVEN, OFF THORNDYKE RD
JEFFERSON COUNTY,WASHINGTON
TEST PIT 1 - See Figure 2
Depth (ft) Soil Type Description
0.0 - 1.0 Topsoil
1.0 - 2.5 SP Rd/Brn SAND w/silt and occ gravel (loose to med dense, moist)
2.5 - 6.0 SP Brn SAND w/occ gravel (loose to med dense, moist)
6.0 - 7.0 SP Brn SAND w/occ gravel (med dense, moist) (small roots to 2.5')
No caving observed
No groundwater seepage observed
TEST PIT 2 - See figure 2
Depth (ft) Soil Type Description
0.0 - 1.0 Topsoil
1.0 - 2.0 SP Rd/Brn SAND w/silt and occ gravel (loose to med dense, moist)
2.0 - 5.0 SP Brn SAND w/occ gravel (loose to med dense, moist)
5.0 - 6.5 SP Brn SAND w/occ gravel (med dense, moist) (small roots to 4')
No caving observed
No groundwater seepage observed
•
Conventional Footing
Residential
' Structure
Slope Greater • Foundation V
Than 30 Percent Setback Distance Element
Footing Extension or Pile Support
I Residential
Structure
Slope Greater NAN Footing as Grade Beam
Than 30 Percent 44,
.4 Footing or Piling
Extension
STRUCTURAL SETBACK
GeoResources V V
FIGURE 6