Towne Place Hotel 2008 01 28 Geotech report (18 pages)GeoResourcesLLC
Ph 253-896-1011 5007 Pacific Hwy. E., Suite 20
Fx 253-896-2633 Fife, Washington 98424
Mr. Dale Sweeney
5715 — 143`d Place SE
Bellevue, Washington 98006
January 28, 2008
Geotechnical Report
Proposed Hotel
34839 Pacific Highway South
Federal Way, Washington
Job Name: Sweeney, D. PacHwyS
INTRODUCTION
This report summarizes the results of our geotechnical engineering services for
the proposed new hotel to be constructed at 34839 Pacific Highway South in Federal
Way, Washington. The approximate location of the site is shown on Figure 1.
Our understanding of the project is based on our discussions with you, our
review of the available project plans and our local experience with similar projects in the
vicinity of the site. We were provided with a preliminary a site plan showing the planned
building location and parking lot configuration. The plan indicates the project will consist
of constructing a new 4-story hotel building in the approximate center of the site with
parking areas provided along all sides. An access driveway will enter the site from
Pacific Highway South at the sites' northeast corner and lead to a porte cochere over the
main building entrance along the north side of the building. Site stormwater will
discharge to a detention pipe located under the south parking lot. The site layout is
shown on the Site Plan, Figure 2.
No topographic site plan was available at the time of our study. However, based
on our observations at the time of our site visit, we expect cuts and fills up to 10 feet to
achieve finish grades. Although specific design details are not available, we expect the
structure will consist of typical spread footing foundations with slab -on -grade floors.
Foundation loads should be in the range of 4 to 6 kips per foot for bearing walls and up
100 kips for isolated columns.
SCOPE
The purpose of our services is to evaluate the surface and subsurface conditions
at the site as a basis for developing and providing geotechnical recommendations and
design criteria for the proposed site development. Specifically, the scope of services for
this project included the following:
1. Conducting a geologic reconnaissance of the site area.
2. Exploring the subsurface conditions at the site by monitoring the excavation
of four track -hoe excavated test pits at selected locations across the site.
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January 28,2008
Page 2
3. Addressing the appropriate geotechnical regulatory requirements for the
proposed site development, including seismic hazards and liquefaction
potential.
4. Providing 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,
and drainage and erosion control measures.
5. Providing recommendations and design criteria for foundation and floor slab
support, including allowable bearing capacity, lateral soil pressures and
estimates of settlement.
6. Providing recommendations for discharge of the site stormwater.
7. Providing recommendations and design criteria for parking lot pavements.
8. Providing recommendations for site drainage.
SITE CONDITIONS
Surface
The approximate 2.5-acre project site is located at 34839 Pacific Highway South
in the city of Federal Way, Washington. The project site is bordered with undeveloped
property to the south and west, a hotel to the north, and Pacific Highway South to the
east. The site is currently developed with a small one-story commercial building in the
northeast corner, a small one-story metal building in the approximate center of the site,
and a few outbuildings at various locations along the east end of the site.
Surface grades at the site slope down to the west at surface inclinations ranging
from 5 to 15 percent. Towards the western end of the site, surface grades increase to
approximately 20 to 35 percent down to a wetland area along the western property line.
The slope down to the wetland along the sites' western property line is approximately 20
feet tall.
The majority of the site is covered with either grass or gravel. The west end of
the site is vegetated with various medium-sized coniferous and deciduous trees with
moderately thick underbrush. No areas of erosion were apparent on the site slopes; no
standing water was observed on the site at the time of our site work.
Soils
The United States Department of Agriculture (USDA) Natural Resource
Conservation Service (NRCS), formerly known as the Soil Conservation Service (SCS),
for King County has mapped the site soils as consisting of Everett-Alderwood gravely
sandy loam (EwC) soils that form on 6 to 15 percent slopes. According to the NRCS,
the Everett-Alderwood soils at the site have a "moderate" potential for erosion when
exposed. We observed no active erosion in the site area during our reconnaissance.
Based on our observations, the site soils will have a low susceptibility to erosion,
particularly where vegetation is established. An excerpt from the NRCS map is provided
in Figure 3.
Geology
According to the Geologic map of the Poverty Bay 7.5 Minute Quadrangle, Washington,
by Derek B. Booth, Howard H. Waldron, and Kathy G. Troost (2003), the site is underlain
by Recessional outwash (Qvr). This soil unit is described as well stratified sand and
gravel deposited by streams and rivers issuing from the front of the receding ice sheet.
It is generally lightly oxidized and commonly very compact. In our opinion, based on the
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January 28, 2008
Page 3
soils observed in our test pits, the site soils would be better classified as glacial Till (Qvt)
This soil unit is described as a compact mixture of sand, gravel, silt and clay. An excerpt
from the USGS map is provided in Figure 4:
Subsurface Explorations
On November 2, 2007, a representative from our office was on site to explore
subsurface conditions at the site by observing the excavation of 4 trackhoe test pits to a
maximum depth of 10 feet below existing surface grades. The approximate test pit
locations are shown on the Site Plan, Figure 2
Our representative continuously monitored the excavations, maintained logs of
the subsurface conditions encountered in each test pit, obtained representative soil
samples, and observed pertinent site features. The specific number, location, and depth
of the explorations were selected by GeoResources personnel in the field. The soils
encountered were visually classified in accordance with the Unified Soil Classification
System (USCS) provided in Figure 5. The explorations performed as part of this
evaluation indicate subsurface conditions at specific locations only and actual
subsurface conditions can vary across the site. Furthermore, the nature and extent of
any such variation would not become evident until additional explorations are performed
or until construction activities have begun. The test pit logs are provided in Figure 5.
Representative soil samples obtained from the test pits were placed in sealed containers
and taken to a laboratory for possible further examination and testing.
Subsurface Conditions
The subsurface conditions encountered in the test pits were fairly uniform. The
soils we observed in the test pits generally consist of 6 inches of topsoil overlying old fill
and silty sand with gravel consistent with glacial till.
In Test Pits TP-1, TP-3 and TP-4, we encountered loose to medium dense, moist
fill consisting of silty sand with gravel and occasional topsoil and construction debris to
depths ranging from 1 to 7 1/2 feet below surface grades. The fill was thicker towards the
west end of the site. Underlying the fill in Test Pits TP-1, TP-3 and TP-4, and in Test Pit
TP-2, we encountered medium dense to dense, moist silty sand with gravel consistent
with glacial till.
We did not encounter groundwater seepage in any of the test pits excavated at
the site. To the depths explored, we did not encounter mottled soils or other evidence
suggesting a seasonal groundwater table develops at the site. However, based on the
mapped stratigraphy of the area and the existence of fill over dense glacial till, we do
anticipate a seasonal [perched groundwater table will develop under the site during the
wet winter months (October through May). This water table will fluctuate seasonally due
to precipitation, and future development both on and near the site.
GEOLOGIC HAZARDS
Erosion
Section 18-28 in the City of Federal Way municipal code defines erosion hazard
areas as those areas having a "severe" or "very severe" erosion hazard due to natural
agents such as wind, rain, splash, frost action or stream flow. The USDA NRCS has
mapped the site soils as Everett-Alderwood soils having a "moderate" potential for
erosion due to rainfall when exposed. Regardless of the erosion classification of the
site, erosion and sediment control measures as required by the city of Federal Way will
need to be in place prior to and during construction activity at the site.
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January 28, 2008
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Landslide
Section 18-28 in the City of Federal Way municipal code defines landslide hazard
areas as those areas potentially subject to episodic downslope movement of a mass of
soil or rock including but not liimited to the followiing areas:
a. Any area with a combination of:
1. Slopes greater than 15 percent;
2. Permeable sediment overlying a relatively impermeable sediment or bedrock;
3. Springs or groundwater seeps.
b. Any area which has shown movement during the Holocene epoch, from 10,000 years
ago to the present, or which is underlain by mass wastage debris of that epoch.
c. Areas potentially unstable as a result of rapid stream incision, stream bank erosion,
and undercutting by wave action.
d. Areas located in a canyon or on an active alluvial fan, presently or potentially subject
to inundation by debris flows or catastrophic flooding.
e. Areas that have a "severe" limitation for building site development because of slope
conditions, according to the USDA SCS.
f. Those areas mapped as Class U (Unstable), Uos (Unstable old slides), and Urs
(unstable recent slides) by the Department of Ecology.
g. Slopes having a gradient steeper than 80 percent subject to rock fall during seismic
shaking.
No evidence of landslide activity, or significant erosion was observed at the site
at the time of our site visit. We did observe slopes steeper than 15 percent but with no
permeable sediment overlying relatively impermeable sediment or bedrock was
observed, and no seepage. No planes of weakness or rockfall hazards were observed at
the site. No other landslide hazard criteria were observed at the site or the immediate
adjacent areas. Based on the above, it does not appear that the site has an active
landslide hazard on or within 25 feet of the property.
Steep Slope
Section 18-28 in the City of Federal Way municipal code defines steep slope
hazard areas as those areas with a slope of 40 percent or greater and with a vertical
relief of 10 or more feet. Based on the topographic map provided to us and our
observations during our site reconnaissance, the site does not have areas sloping
greater than 40 percent with a vertical height of at least 10 feet, therefore the site is not
classified as having steep slope hazard areas.
Seismic
The state of Washington has recently adopted the 2003 International Building
Code (IBC). Based on the soil conditions encountered and the local geology, per
chapter 16 of the 2003 (IBC) site class "C should be used in structural design. This
correlates to Soil Profile Type Sc in the 1997 Uniform Building Code (UBC). This is
based on the inferred range of SPT (Standard Penetration Test) blow counts relative to
trackhoe excavation progress and probing with a'h-inch diameter steel probe rod. The
presence of glacially consolidated soil conditions were assumed to be representative for
the site conditions beyond the depths explored.
Liquefaction is a phenomenon where there is a reduction or complete loss of soil
strength due to an increase in water pressure. The increase in pore water pressure is
induced by vibrations. Liquefaction mainly affects geologically recent deposits of loose,
fine-grained sands that are below the groundwater table. Based on the medium dense
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January 28,2008
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to dense and well -graded nature of the soils observed on the site, and the lack of an
established water table to the depths explored, it is our opinion that there is no risk for
liquefaction to occur at this site during an earthquake.
CONCLUSIONS AND RECOMMENDATIONS
General
Based on our study, it is our opinion soil and groundwater conditions are suitable
for the proposed commercial development. The multi -story structure can be supported
on conventional spread footings bearing on competent native soils or on structural fill
placed above these native soils. Floor slabs and pavements can be similarly supported.
The upper 1 to 71/2 feet of old fill soils observed in Test Pits TP-1, TP-3 and TP-4
contain significant amounts of organics and trash debris and will not be suitable for
support of structural elements, or for use as structural fill. Prior to construction, these
unsuitable old fill soils should be removed from under new foundation and slab -on -grade
areas and from under utility lines and structures. Grade should be restored with new
structural fill. Parking lot pavements can be constructed on the native soils or the
existing fill if the pavement section includes a drainage layer, and the exposed pavement
subgrade can be compacted to a firm and non -yielding condition.
Detailed recommendations regarding these issues and other geotechnical design
considerations are provided in the following sections of this report. These
recommendations should be incorporated into the final design drawings and construction
specifications.
Erosion and Sedimentation Control
The City of Federal Way Municipal code defines erosion hazard areas as those
areas having a severe or very severe erosion hazard due to natural agents such as
wind, rain, splash, frost action or stream flow. As previously discussed, the USDA
NRCS has mapped the site soils as Everett-Alderwood soils having a "moderate"
potential for erosion due to rainfall when exposed. We observed no active erosion on
the site or on the slopes adjacent the site area during our reconnaissance. In our
opinion, the potential for erosion is not a limiting factor in site development. Erosion
hazards can be mitigated by applying Best Management Practices (BMPs) outlined in
the Washington State Department of Ecology's (Ecology) Stormwater Management
Manual for the Puget Sound Basin. Erosion protection measures, as required by the
City of Federal Way, will need to be in place prior to starting grading activity on the site.
If the required erosion and sediment control BMPs are properly implemented and
maintained, it is our opinion that the planned development will not increase the potential
for erosion at the site or on adjacent properties. Similarly, it is our opinion that the
planned development will not increase the potential for site instability resulting from
erosion or added sediment transport to the watercourse along the west end of the
property.
Site Preparation and Grading
To prepare the site for construction, all vegetation, organic surface soils, and
other deleterious materials including any existing structures, foundations or abandoned
utility lines should be stripped and removed from the site. Organic topsoil and the old fill
containing organic and trash debris will not be suitable for use as structural fill, but may
be used for limited depths in non-structural areas. Prior to construction, the existing fill
containing topsoil and trash debris should be removed from under new foundation and
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January 28, 2008
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slab -on -grade areas and from under the site utility lines and utility structures. Stripping
depths ranging from 1 to 7 1/2 feet should be expected to remove these unsuitable soils.
Once clearing and stripping operations are complete, cut and fill operations can
be initiated to establish desired grades. Prior to placing fill, all exposed surfaces should
be proofrolled or probed to determine if any isolated soft and yielding areas are present.
Proofrolling should also be performed in cut areas that will provide direct support for new
construction. We recommend that a member of our staff evaluate the exposed subgrade
conditions after removal of vegetation and topsoil stripping is completed and prior to
placement of structural fill. If excessively yielding areas are observed and cannot be
stabilized in place by compaction, the affected soils should be excavated and removed
to firm bearing soil and grade restored with new structural fill. The depth and extent of
overexcavation should be evaluated by our field representative at the time of
construction.
Suitability of On -Site Materials as Fill
Our study indicates the native soils are currently in a moist condition and contain
a relatively high percentage of fines (silt and clay -size particles), which will make them
difficult to use as structural fill in wet weather conditions. The existing fill soils contain
varying amounts of organic and construction debris, which will make them unsuitable for
use as structural fill. Accordingly, the ability to use the native and fill soils from site
excavations as structural fill will depend on their moisture content, organic and
construction debris content, and the prevailing weather conditions when site grading
activities take place.
If structural fill will be imported to the site and grading activities are planned
during the wet winter months, or if they are initiated during the summer and extend into
fall and winter, the owner should be prepared to import a wet weather structural fill. For
this purpose, we recommend importing a wet weather structural fill as described in the
"Structural Fill" Section of this report.
Structural Fill
All fill placed to establish finish grades and utility trench backfill should be placed as
structural fill. 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. For planning purposes, we
recommend a maximum loose -lift thickness of 12 inches. We recommend that our
representative be present during site grading activities to observe the work and perform
field density tests.
Fill should be compacted to at least 95 percent of the soils laboratory maximum dry
density (MDD) as determined in accordance with ASTM D-1557 (Modified Proctor). The
moisture content of the soil at the time of compaction should be within two percent of its
optimum, as determined by this same ASTM standard.
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 the No. 200 sieve)
increases, soil becomes increasingly sensitive to small changes in moisture content and
compaction becomes more difficult to achieve. During wet weather, we recommend
using a well -graded sand and gravel with less than 5 percent (by weight) passing the
No. 200 sieve based on that fraction passing the 3/4-inch sieve. If prolonged dry
weather prevails during the earthwork and foundation installation phase of construction,
a slightly higher (up to 10 to 12 percent) fines content will be acceptable.
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January 28, 2008
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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.
Building Setback
Based on the soils encountered in the test pits, the mapped stratigraphy of the
site, our site observations and our conclusion regarding site stability, it is our opinion that
the site slopes do not constitute a landslide or steep slope hazard and therefore no
geologic hazard area buffer is necessary. However, the City of Federal Way building
department may require a building setback in accordance with IBC standard
requirements. The IBC does require a building setback from slopes that are greater than
30 percent. According to the IBC, when the geotechnical report demonstrates that a
reduced or eliminated setback, together with design and engineering solutions, will meet
the intent of the chapter, such reduced or eliminated setback and design and
engineering solutions may be permitted. Vegetation in the setback area may be
enhanced, if approved/required by the City of Federal Way. Clearing, grading and filling
within the setback area is allowed if it can be demonstrated that the existing vegetation
will not be adversely impacted or that it can be mitigated (enhanced).
In our opinion, the foundations for the structure should be provided with at least a
15-foot setback from the site slopes with surface inclinations that exceed 30 percent in
accordance with the 2003 International Building Code (IBC). Where necessary, the
building setback for the house foundations may be measured horizontally from the lower
outside edge of the footing to the face of the steep slope, in accordance with UBC/IBC.
Where this `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 the medium dense to dense native
soils. Maintaining the prescribed setback in this manner provides the conventional
foundation bearing prism beneath the footing.
Weathering, erosion and the resulting surficial sloughing and shallow land sliding
are natural processes that affect steep slope areas. As noted, no evidence of surficial
raveling or sloughing was observed at the site. To manage and reduce the potential for
these natural processes, we recommend the following:
No drainage of concentrated surface water or significant sheet flow onto or near
the steep slope areas. Drainage from the roof area should be tightlined to flatter,
lowland area beyond the toe of the steep slope.
No fill should be placed within the setback area. Grading should be limited to
providing surface grades that promote surface flows away from the slope crest to
an approved point of collection for dispersal beyond the toe of the slope.
No percolation of surface water within 20 feet of Building Setback or top of the
steep slope.
Excavations
All excavations at the site associated with confined spaces, such as utility
trenches and retaining walls, must be completed in accordance with local, state, or
federal requirements. Based on current Washington State Safety and Health
Administration (WSHA) regulations, the upper loose to medium dense fill and silty sand
with gravel observed on the site would be classified as Type C soils. The deeper, dense
silty sand with gravel at the site would be classified as Type A soils.
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January 28, 2008
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According to WSHA, for temporary excavations of less than 20 feet in depth, the
side slopes in Type C soils should be laid back at a slope inclination of 1.5:1
(Horizontal:Vertical) or flatter from the toe to the crest of the slope. Side slopes in Type
A soils can be laid back at a slope inclination of 0.75:1. All exposed slope faces should
be covered with a durable reinforced plastic membrane during construction to prevent
slope raveling and rutting during periods of precipitation. 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,
or if construction materials will be stockpiled along the slope crest. If these safe
temporary slope inclinations cannot be achieved due to property line constraints, shoring
may be necessary.
This information is provided solely for the benefit of the owner and other design
consultants, and should not be construed to imply that GeoResources assumes
responsibility for job site safety. It is understood that job site safety is the sole
responsibility of the project contractor.
Foundations
The structure can be supported on conventional spread footing foundations
bearing on competent native soils or on new structural fills placed above these native
soils. Foundation subgrades should be prepared as recommended in the "Site
Preparation" section of this report. As previously discussed, the upper 1 to 7'/2 feet of
old fill soils observed in Test Pits TP-1, TP-3 and TP-4 contain significant amounts of
organics and construction debris and will not be suitable for support of foundation
elments. Prior to construction, these unsuitable old fill soils should be removed from
under new foundation areas and replaced with new structural fill. Alternatively, the
foundations can be deepened to extend through the old fill to bear on the underlying
undisturbed native soils observed at 1 to 7'/2 feet below surface grades.
Perimeter foundations exposed to the weather should bear at a minimum depth
of 18 inches below final exterior grades for frost protection. Interior foundations can be
constructed at any convenient depth below the floor slab. With footings founded as
recommended, we recommend they be designed for an allowable soil bearing capacity
of 2,500 pounds per square foot (psf) for combined dead and long-term live loads. The
weight of the footing and any overlying backfill should be neglected. The allowable
bearing value may be increased by one-third for short-term loads such as those induced
by seismic events or wind loads. With the anticipated loads and this bearing stress
applied, building settlements should be less than one-half inch total and one -quarter inch
differential. All footing areas should be evaluated by a representative of GeoResources
prior to placement of forms.
For designing foundations to resist lateral loads, a base friction coefficient of 0.40
can be used. Passive earth pressures acting on the sides of the footings can also be
considered. We recommend calculating this lateral resistance using an equivalent fluid
weight of 325 pounds per cubic foot (pcf). We recommend not including the upper 12
inches of soil in this computation because it can be affected by weather or disturbed by
future grading activity. This value assumes the foundations will be constructed neat
against competent native soil or backfilled with structural fill, as described in the
"Structural Fill" section of this report. The values recommended include a safety factor
Of 1.5.
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January 28, 2008
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Site Retaining Walls
The magnitude of earth pressure development on below -grade walls, such as
basement or retaining walls, will partly depend on the quality of the wall backfill. We
recommend placing and compacting wall backfill as structural fill. Wall backfill below
structurally loaded areas, such as pavements or floor slabs, should be compacted
according to the specifications provided in the "Structural Fill" section of this report.
To guard against hydrostatic pressure development, drainage must be installed
behind the wall. We recommend that wall drainage consist of a minimum 12 inches of
clean sand and/or gravel with less than 3 percent fines placed against the back of the wall.
In addition, a drainage collector system consisting of 4-inch perforated PVC pipe should
be installed behind the wall to provide an outlet for any accumulated water. The drains
should be provided with cleanouts at easily accessible locations. These cleanouts
should be serviced at least once every year. The wall drainage material should be
capped at the ground surface with 1-foot of relatively impermeable soil to prevent surface
intrusion into the drainage zone.
With wall backfill placed and compacted as recommended and drainage properly
installed, unrestrained walls can be designed for an active earth pressure equivalent to a
fluid weighing 35 pcf. For restrained walls, we do not recommend using at rest earth
pressures. For walls that will be restrained at the top, an additional uniform lateral
pressure of 100 psf should be included. These values assume a horizontal backfill
condition and that no other surcharge loading, such as traffic, sloping embankments, or
adjacent buildings, will act on the wall. If such conditions exist, then the imposed
surcharge loading must be included in the wall design. Friction at the base of the wall
foundation and passive earth pressure will provide resistance to these lateral loads.
Values for these parameters are provided in the "Foundations" section of this report.
Slab -On -Grade Floors
Slab -on -grade floors should be supported on subgrades prepared as recommended
in the "Site Preparation" section of this report. As previously discussed, the upper 1 to
7 1/2 feet of old fill soils observed in Test Pits TP-1, TP-3 and TP-4 contain significant
amounts of organics and construction debris and will not be suitable for support of slab -
on -grade floors. Prior to construction, these unsuitable old fill soils should be removed
from under new slab -on -grade areas and replaced with new structural fill.
Immediately below the floor slab, we recommend placing a four -inch thick capillary
break layer of clean, free -draining, coarse sand or fine gravel that has less than three
percent passing the No. 200 sieve. This material will reduce the potential for upward
capillary movement of water through the underlying soil and subsequent wetting of the
floor slabs. The drainage material should be placed in one lift and compacted to a firm
and unyielding condition.
The capillary break layer will not prevent moisture intrusion through the slab
caused by water vapor transmission. Where moisture by vapor transmission is
undesirable, such as covered floor areas, a common practice is to place a durable
plastic membrane on the capillary break layer and then cover the membrane with a layer
of clean sand or fine gravel to protect it from damage during construction, and aid in
uniform curing of the concrete slab. It should be noted that if the sand or gravel layer
overlying the membrane is saturated prior to pouring the slab, it will not assist in uniform
curing of the slab, and may serve as a water supply for moisture transmission through
the slab and affecting floor coverings. Therefore, in our opinion, covering the membrane
with a layer of sand or gravel should be avoided if floor slab construction occurs during
the wet winter months and the layer cannot be effectively drained.
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January 28, 2008
Page 10
Parking Lot Pavement
Parking lot pavement at the project site should be constructed on subgrades
prepared as recommended in the "Site Preparation" section of this report. As
previously discussed, the upper 1 to 71/2 feet of old fill soils observed in Test Pits TP-1,
TP-3 and TP-4 contain significant amounts of organics and trash debris. Prior to paving,
these existing fill soils should be mechanically compacted to a firm and non -yield
condition. Additionally, the pavement section should be provided with a drainage layer
between the asphalt and the underlying compacted subgrade soils.
The thickness of the various components of the pavement depends on the
subgrade soils and the traffic conditions to which the pavement will be subjected. We
expect traffic to mainly consist of light passenger vehicles, with only occasional heavy
service vehicles. Based on this information, and with a properly prepared and stable
subgrade composed of on -site native granular soils, or compacted old fill soils, we
recommend the following pavement section:
Options
Pavement Element
Thickness
(inches)
Option 1
Asphalt Concrete (AC)
3
Crushed Rock Base (CRB)
4
Option 2
Asphalt Concrete (AC)
2
Asphalt Treated Base (ATB)
3
Crushed Rock Base (CRB)
4
All paving materials should conform to the Washington State Department of
Transportation (WSDOT) specifications for Class B asphalt concrete and CRB surfacing.
Long-term pavement performance will depend on surface drainage. A poorly -drained
pavement section will be subject to premature failure as a result of surface water
infiltrating into the subgrade soils and reducing their supporting capability. To improve
performance, we recommend surface drainage gradients of at least two percent. Some
longitudinal and transverse cracking of the pavement surface should be expected over
time. Regular maintenance should be planned to seal cracks when they occur
Regardless of the relative compaction achieved, the subgrade must be firm and
unyielding before paving. Proofrolling the subgrade with heavy construction equipment
should be completed to verify this condition. We recommend compacting fill placed for
pavement subgrades according to the recommendations provided in the "Structural
Fill" section of this report.
Stormwater Detention Pipe
The site stormwater will discharge to a detention pipe located under the south
parking lot. We understand the detention pipe will entail storage and a stormfilter for
cleaning prior to discharge to the wetland located along the west end of the site. The
detention pipe should be supported on a subgrade prepared as recommended in the "Site
Preparation" section of this report. Accordingly, if the existing old fill containing organics
Dale Sweeney
January 28, 2008
Page 11
and construction debris is evident along the pipe subgrade, it should be removed and
replaced with new structural fill.
We examined the existing soils underlying the site to determine if infiltration of
the development stormwater was feasible. Due to the medium dense to dense, well -
graded, and cemented nature of the native glacial till soils that underlie the site, it is our
opinion that infiltration of the site stormwater is not feasible. It is also our opinion that
the planned stormwater detention system will not increase the stability of the site slopes
Utilities
We expect that underground utilities, such as sanitary sewer, storm, and water
will consist of a series of pipes, vaults, manholes, and catch basins. The utility
excavations should be performed in accordance with appropriate governmental
guidelines. Utility pipes should be bedded and backfilled in accordance with American
Public Works Association (APWA) specifications. The existing fill at the site containing
organics and trash debris will not be suitable for support of the utility lines and
structures. Prior to construction, these unsuitable old fill soils should be removed from
under the utility lines and structures.
We anticipate that the on -site, non -organic soils will be suitable for use as
structural backfill. If import soil is used as utility trench backfill, it should consist of a
material meeting the wet weather fill recommendations provided in the "Structural Fill"
section of this report. Controlled -density fill (CDF) is most often suitable for use as
backfill in any weather condition and could be used as a convenient, but more
expensive, alternative to granular backfill soil.
We recommend that utility backfill soils be compacted according to the
recommendations provided in the "Structural Fill" section of this report. CDF backfill
does not require compaction but should have a compressive strength commensurate
with the application.
Drainage
All ground surfaces, pavements, and sidewalks should be sloped away from the
structure. Surface water runoff should be controlled using a system of berms, drainage
swales, and/or catchbasins, and conveyed to an approved point of controlled discharge.
We recommend conventional roof and foundation drains be installed for all structures.
The footing drains should be tightlined independent of the roof drains unless an
adequate gradient will prevent backf low into the footing drains
Surface water shall not be allowed to flow uncontrolled over the crest of the site
slopes and embankments. Surface water should be directed away from the slope crests
to a point of collection and controlled discharge. If constructed according to code, a
dispersion trench would be considered a controlled discharge mechanism. If site grades
do not allow for directing surface water away from the slopes, then the collected water
should be tightlined down the slope face in a controlled manner.
LIMITATIONS
We have prepared this supplemental report for use by Dale Sweeney and
members of their design team for use in the design and permitting portions of this
project. This report and the data used in preparing this report should be provided to
prospective contractors for 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.
Dale Sweeney
January 28, 2008
Page 12
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 antici-
pated, and to evaluate whether earthwork and foundation installation activities comply
with contract plans and specifications.
When the project design is finalized, we recommend the design and
specifications be reviewed by our firm to see that our recommendations have been
interpreted and implemented as intended. 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.
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.
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, expressed or implied, should be understood.
Mm
We appreciate the opportunity to be of continued service to you on this project.
Please do not hesitate to call with any additional comments or questions.
EX?IRES jJ- 08-zo08
Bernard P. Knoll 11, PE
Senior Engineer
BPK:BPB:bpk
Document ID: Sweeney,D.PacificHighwayS.GR
Attachments: Figure 1 —Site Vicinity Map
Figure 2 — Site Plan
Figure 3 — USDA NRCS Soils Map
Figure 4 — USGS Map
Figure 5 — Unified Soil Classification System (USCS)
Figure 6 — Test Pit Logs
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Approximate Site Location
5007 Pacific Highway East, Suite 20
Fife, Washington 98424
Phone: 253-896-1011
Fax: 253-896-2633
Site Vicinity Map
34839 Pacific Highway South
Federal Way, Washington
Job #: Sweeney,D.PacificHwyS I January 2008 1 Figure 1
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Site plan provided by TNT Engineering.
APPROXIMATE TEST PIT LOCATION
APPROXIMATE LOCATION OF SLOPES > 40%
APPROXIMATE LOCATION OF SLOPES > 15 - 39%
fp
9
100 Mil
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APPROXIMATE SCALE
1"=30'
GeoResources, LLC
5007 Pacific Highway East, Suite 20
Fife, Washington 98424
Ph:253-896-1011 Fax:253-896-2633
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EXISTING
ONE 57
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Site Plan
34839 Pacific Highway South
Federal Way, Washington
Job #: Sweeney,D.PacificHwyS
January 2008
Approximate
t
GeoResources, LLC
5007 Pacific Highway East, Suite 20
Fife, Washington 98424
Phone: 253-896-1011
Fax: 253-896-2633
Location
Map Unit Symbol ', Map Unit Name Acres in Percent of
AOI AOI
EwC 2.4 100.00l0
Totals for Area of Interest 2.4 100.0%
(AOI)
USDA MRCS Map
34839 Pacific Highway South
Federal Way, Washington
Approximate Site Location
GeoResources, LLC
5007 Pacific Highway East, Suite 20
Fife, Washington 98424
Phone: 253-896-1011
Fax: 253-896-2633
USGS Map
34839 Pacific Highway South
Federal Way, Washington
UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GROUP
SYMBOL
GROUP NAME
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
GC
CLAYEY GRAVEL
No. 4 Sieve
More than 50
SAND
CLEAN SAND
SW
WELL -GRADED SAND, FINE TO COARSE SAND
SP
POORLY -GRADED SAND
Retained on
No. 200 Sieve
More than 50%
Of Coarse Fraction
SAND
SM
SILTY SAND
Passes
WITH FINES
SC
CLAYEY SAND
No. 4 Sieve
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 Limn
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
5007 Pacific Highway East, Suite 20
Fife, Washington 98424
Phone: 253-896-1011
Fax: 253-896-2633
Unified Soil Classification System (USCS)
34839 Pacific Highway South
Federal Way, Washington
Job #: Sweeney. D.PacificHwyS I January 2008 Figure 5
Test Pit TP-1
Location: See Site Plan
Depth
(ft.) Soil Type Description
(3 inches grass roots and TOPSOIL)
0.0 -
4.0 FILL: Gray and brown silty sand with gravel and cobbles, loose to medium
dense, moist. (Fill was organic -laced from 3 to 4 feet.)
4.0 -
6.5 SM Brownish -orange silty SAND with gravel, slightly cemented, medium dense,
moist. (Weathered Glacial Till)
6.5 -
8.0 SM Gray silty SAND with gravel, moderately cemented, dense. (Glacial Till)
Terminated at 8 feet below the ground surface.
No caving observed.
No groundwater observed.
Test Pit TP-2
Location: See Site Plan
Depth
(ft.) Soil Type Description
(2 inches grass roots and TOPSOIL)
0.0 -
3.5 SM Gray silty SAND with gravel, moderately cemented, dense. (Glacial Till)
Terminated at 3'/2 feet below the ground surface.
No caving observed.
No groundwater observed.
Test Pit TP-3
Location: See Site Plan
Depth
(ft.) Soil Type Description
(4 inches grass roots and TOPSOIL)
0.0 -
7.5 FILL: Gray and brown silty sand with gravel and cobbles, loose to medium
dense, moist to wet. (Fill was organic -laced with construction debris and a
strong organic odor from 5 to 7 Y2 feet.)
7.5 -
9.0 SM Brownish -orange silty SAND with gravel, slightly cemented, medium dense,
moist. (Weathered Glacial Till)
9.0 -
10.0 SM Gray silty SAND with gravel, moderately cemented, dense. (Glacial Till)
Terminated at 10 feet below the ground surface.
No caving observed.
No groundwater observed.
Test Pit TP-4
Location: See Site Plan
_ Depth
(ft.) Soil Type Description
(2 inches grass roots and TOPSOIL)
0.0 -
1.0 FILL: Brown silty sand with gravel loose to medium dense, moist.
1.0 -
4.0 SM Brownish -orange silty SAND with gravel, slightly cemented, medium dense,
moist. (Weathered Glacial Till)
4.0 -
6.0 SM Gray silty SAND with gravel, moderately cemented, dense. (Glacial Till)
Terminated at 6 feet below the ground surface.
No caving observed.
No groundwater observed.
GeoResources,
LLC
Test Pit Logs
5007 Pacific Highway East, Suite 20
34839 Pacific Highway South
Fife, Washington 98424
Phone: 253-896-1011
Federal Way,Washington
Fax:
253-896-2633
Job # : Sweeney,D.PacificHwyS
January 2008
Figure 6