23-105365-ANK SP_Geotech Report_12.27.23
August 28, 2023
Asegedom Woldetekle
28950 – 18th Avenue South
Federal Way, Washington 98003
Updated Geotechnical Engineering
Report
Proposed Short Plat
29850 – 18th Avenue South
Federal Way, Washington
PN: 3674400-155,-160
Doc ID: Woldetekle18thAveS.RG
INTRODUCTION
This Updated Geotechnical Engineering Report summarizes our site observations, subsurface
explorations, laboratory testing and engineering analyses, and provides geotechnical
recommendations and design criteria for the proposed short plat to be constructed at 29850 – 18th
Avenue South in Federal Way, Washington. The approximate location of the site shown on the Site
Location Map, Figure 1.
Our understanding of the project is based on our conversations with Svetlana Poblete; our
previous work at the site; our review of the Preliminary Site Plan prepared by DMP Inc. dated April 21,
2023; our July 3, 2023, site visit and additional explorations, our previous work at the site; and our
experience with City of Federal Way development codes. We previously completed a Revised
Geotechnical Engineering Report for the site dated September 22, 2011. Because the report is older
than 5 years, the report needs to be updated. Furthermore, a retaining wall is now proposed on the
eastern property boundary, and the City of Federal Way development codes have changed,
necessitating an updated report. Based on the topography obtained on the King County iMap, and
the Preliminary Site Plan, we anticipate the proposed wall will be a concrete cast-in-place retaining wall.
The proposed plat layout is presented on the Site & Exploration Plan, Figure 2.
PURPOSE & SCOPE
The purpose of our services was to evaluate the surface and subsurface conditions across the
site as a basis for addressing the City of Federal Way development codes as well as providing
geotechnical recommendations and design criteria for the proposed short plat. Specifically, the scope
of services for this project included the following:
1. Reviewing the available geologic, hydrogeologic, and geotechnical data for the site area ;
2. Performing two hand borings with porter sampling in the eastern portion of the site; and,
3. Updating our previously written Revised Geotechnical Engineering Report with the new
development codes, specifically, updating to the 2018 IBC, and summarizing our site
observations, conclusions, and our geotechnical recommendations and design criteria, along
with the supporting data.
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The above scope of work was summarized in our Proposal for Geotechnical Engineering Services
dated June 14, 2023. We received written authorization to proceed June 19, 2023.
SITE CONDITIONS
Surface Conditions
The site consists of two contiguous tax parcels located at 29850 – 18th Avenue South in Federal
Way, Washington. According to the provided Site Plan and King County iMap, the parcels, when
combined, are irregular in shape, measures approximately 180 feet wide (north to south) by
approximately 405 to 460 feet long (east to west) and encompasses approximately 1.73 acres. The
site is bounded by existing residential development to the north, east, and south, and by 18th Avenue
South to the west.
According to topographic information obtained from King County iMap and our site
observations, the ground surface of the site generally slopes up to the east from 18th Avenue South.
From 18th Avenue South, the ground surface slopes up to the east at approximately 15 to 20 percent
over a topographic relief of approximately 10 feet. In the central and eastern portions of the site, the
ground surface slopes up to the west at approximately 2 to 5 percent. Along the eastern extent of the
site, the ground surface slopes steeply up to the west at approximately 40 to 60 percent over a
topographic relief of approximately 20 feet. The total topographic relief of the site is on the order of
40 feet. The existing site layout and topography is shown on the Site Vicinity Map, Figure 3.
Vegetation across the flatter cleared area of the site generally consists of maintained grass
lawn and typical residential landscaping. The eastern slope is vegetated with mixed conifers and
scattered deciduous trees. No seeps, springs, or standing water was observed during our site
reconnaissance. No signs of erosion or slope instability were observed during our site visit.
Site Soils
The USDA Natural Resource Conservation Service (NRCS) Web Soil Survey for King County
indicates the site soils are Alderwood gravelly sandy loam (AgC and AgD) soils and Arents, Alderwood
material (AmB). An excerpt of the soils map for this area is provided as Figure 4.
• Alderwood gravelly sandy loam (AgC and AgD): The Alderwood soils are derived from glacial drift
and/or glacial outwash over dense glaciomarine deposits and are included in hydrologic soils
group B. The AgC soils are mapped as underlying the southwest corner of the site, form on
slopes of 8 to 15 percent, and are considered to have a “moderate” erosion hazard when
exposed. The AgD soils are mapped as underlying the eastern portion of the site, form on
slopes of 15 to 30 percent, and are considered to have a “moderate to severe” erosion hazard
when exposed.
• Arents, Alderwood material (AmD): The Arents soils are mapped as underlying the majority of
the site These soils are derived from basal till, form on slopes of 0 to 6 percent, are considered
to have a “slight” erosion hazard when exposed, and are included in hydrologic soils group
B/D.
Site Geology
The Lidar-revised geologic map of the Poverty Bay 7.5’ quadrangle, King and Pierce Counties,
Washington (Tabor et al, 2014) maps the site geology as being underlain by Glacial Till (Qvt) with
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Advance Outwash Deposits (Qva) being mapped to the west of the site. No landslides, mass wastage
deposits, or alluvial fans are mapped on or within the site vicinity. An excerpt of the above referenced
geologic map is attached as Figure 5 and detailed descriptions of the geologic units mapped in the
site area are included below.
• Glacial till (Qvt): Glacial till typically consists of a heterogeneous mixture of clay, silt, and sand,
and gravel that was deposited at the base of the prehistoric continental glacial ice mass and was
subsequently over-ridden. As such, glacial till is considered over-consolidated and exhibits high
strength and low compressibility characteristics where undisturbed. Infiltration feasibility in
these soils is generally poor.
• Advance outwash (Qva): Advance outwash was deposited by meltwater stream emanating from
the advancing ice mass and generally consists of well graded, lightly stratified to locally cross -
bedded mixtures of sand and gravel. These soils are considered to be over-consolidated and
offer moderate to high strength characteristics when undisturbed. Infiltration p otential is
generally favorable based on grain size but can vary.
We reviewed both the WA Department of Natural Resources (WA DNR) 2017 Landslide
Compilation and the Landslide Inventory datasets for the site vicinity. The Landslide Inventory dataset
maps landslide landforms based on criteria provided in the Protocol for Landslide Mapping from LiDAR
Data in Washington State (Slaughter, et al, 2017) and the Oregon Department of Geology and Mineral
Industries (DOGAMI) protocol described in Special Paper 42 (Burns and Madin, 2009. The WA DNR
Landslide inventory does not map the site for “moderate” or “high” susceptibly to shallow or deep
landslides. No landslides are mapped within 300 feet of the subject site.
Subsurface Explorations
On July 28, 2011, a representative from GeoResources, LLC (GeoResources) visited the site and
monitored the excavation of five test pits to depths of approximately 7 to 12 feet below the existing
ground surface, logged the subsurface conditions encountered in each test pit, and obtained
representative soil samples. The test pits were excavated by a small track -mounted excavator
operated by a licensed earthwork contractor working under subcontract for GeoResournces. The
number and location of our test pits were selected in the field based on project information provided
by you at the time of excavation, our understanding of the proposed development, consideration for
underground utilities, existing site conditions, and current site usage.
On July 3, 2023, we returned to the site and excavated two hand borings to depths of 4½ to
5½ feet below the existing grades, where refusal conditions were encountered. Our field
representatives logged the subsurface conditions encountered in each exploration and obtaine d
representative soil samples. The locations, and depths of our hand boring explorations were selected
based on our understanding of the location of the proposed retaining wall and were adjusted in the
field based on consideration for underground utilities, existing site conditions, site access limitations,
and encountered stratigraphy. Field representatives from our office completed logs of the subsurface
conditions encountered, obtained representative soil samples, and observed pertinent site features.
Representative soil samples obtained from the explorations were placed in sealed plastic bags and
taken to our laboratory for further examination and testing as deemed necessary.
Relatively disturbed, but representative, soil samples were obtained at selec ted depths using
portable Porter soil sampling equipment. The hand-operated equipment consists of a 1.4-inch
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outside-diameter (1.0 inch inside-diameter) split-spoon sampler connected to extension rods of the
same diameter as the barrel. The Porter sampling method consists of driving the sampler 18-inches
into the soil with a 45-pound weight, with a drop of 18 inches. The number of blows required to drive
the sampler through each 6-inch interval is counted, and the total number of blows struck during the
final 12 inches is recorded as the Porter Penetration Test (PPT). If a total of 50 blows are recorded
within any 6-inch interval (refusal), the driving is stopped, and the blow counts are recorded as 50
blows for the actual distance the sampler was driven. The resulting PPT values indicate the relative
density of granular soils and the consistency of cohesive soils , and the energy and size of the test are
correlated to approximately match the values that would be obtained from a Standard Penetration
Test.
The subsurface explorations excavated as part of this evaluation indicate the subsurface
conditions at specific locations only, as actual subsurface conditions can vary across the site.
Furthermore, the nature and extent of such variation would not become evident until additional
explorations are performed or until construction activities have begun. The soil densities presented
on the test pit logs are based on the difficulty of excavation and our experience. Representative soil
samples obtained from the explorations were placed in sealed plastic bags and taken to our
laboratory for further examination and testing as deemed necessary.
The number and approximate locations of our test pits are shown on the Site & Exploration
Plan, Figure 2. The locations depicted were determined by pacing or taping from existing site features
and reference points; as such, the locations should only be considered as accurate as implied by the
method of measurement. The soils encountered were visually classified in accordance with the
Unified Soil Classification System (USCS) and ASTM D2488. The USCS is included in Appendix A as
Figure A-1, while the descriptive logs of our test pits are included as Figures A-2 through A-3.
TABLE 1:
APPROXIMATE LOCATIONS, ELEVATIONS, AND DEPTHS OF EXPLORATIONS
Test Pit
Number Functional Location
Surface
Elevation1
(feet)
Termination
Depth
(feet)
Termination
Elevation1
(feet)
TP-1
TP-2
TP-3
TP-4
TP-5
Southeast portion of site
Central portion of site
Northeast portion of site
Central portion of site
Northwest portion of site
465
462
465
461
458
7½
8½
7
12
10½
457½
453½
458
449
447½
HB-1
HB-2
Northeast corner of site
Eastern portion of site
475
480
5½
4½
469½
475½
Notes:
1 = Surface elevations estimated by interpolating between contours on King County iMap (NAVD88)
Subsurface Conditions
At the location of our explorations, we encountered somewhat uniform subsurface conditions
that, in our opinion, generally confirmed the mapped stratigraphy. In general, we observed topsoil
mantling weathered glacial till, underlain by undisturbed glacial till. These different soil layers are
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described below, and Table 2, below, summarizes the approximate thicknesses, depths, and
elevations of selected soil layers. Logs of explorations are available in Appendix A.
• Topsoil: At the locations explored, we encountered approximately ½ to 2½ feet of topsoil.
• Weathered Glacial Till: Underlying the topsoil in all explorations except for test pits TP-1, we
encountered approximately 1½ to 3 feet of brown silty sand with variable amounts of gravel
in a loose to medium dense, moist condition. We interpret these soils to be weathered glacial
till.
• Glacial till: Underlying the topsoil and weathered glacial till encountered in all other
explorations, we encountered grey gravelly silty sand in a dense to very dense, moist
condition. We interpret these soils to be glacial till. The glacial till was encountered to the full
depth explored in all explorations.
TABLE 2:
APPROXIMATE THICKNESS, DEPTHS, AND ELEVATION OF SOIL TYPES ENCOUNTERED
Exploration
Number
Thickness of
Topsoil
(feet)
Thickness of Weathered
Glacial Till
(feet)
Depth to
Undisturbed
Glacial Till
(feet)
Elevation1 of Glacial
Till
(feet)
TP-1
TP-2
TP-3
TP-4
TP-5
NE
1½
½
1
½
2
1¾
3
2¾
3¼
2
3¼
3½
3¾
3¾
463
458¾
461½
457¼
454¼
HB-1
HB-2
2½
1½
1½
1½
4
3
471
477
Notes:
1 = Surface elevations estimated by interpolating between contours obtained from King County iMap (NAVD88)
NE=Not Encountered
Laboratory Testing
Geotechnical laboratory tests were performed on select samples retrieved from our
explorations to estimate index engineering properties of the soils encountered. Laboratory testing
included visual soil classification per ASTM D2488 and ASTM D2487, moisture content determinations
per ASTM D2216, and grain size analyses per ASTM D6913 standard procedures. The results of the
laboratory tests are included in Appendix B and summarized below in Table 3.
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Groundwater Conditions
No groundwater seepage was observed at the time the test pits and hand borings were
excavated; however, the explorations were excavated during the dry season months. Orange iron oxide
staining, otherwise known as mottling, which can be evidence of a perched groundwater table was
observed in test pit TP-4 and test pit TP-5 at approximately 2½ and 2 feet below ground surface
respectively. The stratigraphy observed at each test pit typically creates the conditions for the
development of perched groundwater following wet weather.
Perched groundwater develops when the vertical and/or horizontal infiltration of stormwater
runoff is slowed or impeded by a soil with low permeability, such as the undisturbed glacial till observed
at each test pit. Accordingly, soil conditions that consist of relatively permeable soils overlying relatively
impermeable soils near the surface are typically necessary. Perched groundwater tables, by definition,
are located within a shallow unconfined aquifer that overlies an aquitard. Perched groundwater tables
are typically limited in thickness and can vary widely in lateral extent. Relatively rapid fluctuations of
groundwater levels should be expected with seasonality and precipitation events, which may include
complete dehydration of the aquifer during the dry season.
CONCLUSIONS AND RECOMMENDATIONS
Based on the results of our data review, site reconnaissance, subsurface explorations and our
experience in the area, it is our opinion that site is suitable for the proposed development from a
geotechnical standpoint. Pertinent updated conclusions and geotechnical recommendations
regarding the design and construction of the proposed development, consistent with the current
building code and stormwater manual are presented below.
The City of Federal Way Critical Areas Ordinance for Geologically Hazardous Areas state
“geologically hazardous areas shall mean areas that, because of their susceptibility to erosion,
landsliding, seismic or other geological events, are not suited to siti ng commercial, residential or
industrial development consistent with public health or safety concerns.” Applicable sections of the
Federal Way Revised Code are included below in italics, and our analysis immediately follows. Based
on our site reconnaissance and literature review, we do not interpret the site to be located in a
Geologically Hazardous Area.
Erosion Hazard Areas per Federal Way Revised Code
The FWRC, Chapter 19.05.070.G(1) defines erosion hazard areas as:
“those areas identified by the U.S. Department of Agriculture’s (USDA) Natural
Resource Conservation Service (NRCS) as having a moderate to severe or severe to very
TABLE 3:
LABORATORY TEST RESULTS FOR ON-SITE SOILS
Sample Soil
Type
Gravel
Content
(percent)
Sand
Content
(percent)
Silt/Clay
Content
(percent)
D10 Ratio
TP-3, S-1, D: ½ -3’ SM 26.9 56.1 17.0 <0.075
TP-5, S-1, D: ½ -2½’ SM 32.2 52.9 14.9 <0.075
HB-1, S-4, D: 4½’ SM 23.5 50.1 26.4 <0.075
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severe rill and inter-rill erosion hazard due to natural agents such as wind, rain, splash,
frost action or stream flow; those areas containing the following group of soils when they
occur on slopes of 15 percent or greater: Alderwood-Kitsap (“AkF”), Alderwood gravelly
sandy loam (“AgD”), Kitsap silt loam (“KpD”), Everett (“EvD”), and Indianola (“InD”); and those
areas impacted by shore land and/or stream bank erosion”
The site soils are mapped as Alderwood gravelly sandy loam (AgC and AgD) and Arents,
Alderwood material (AmB) being mapped upslope from the site. The site is not impacted by shoreline
or subject to stream bank erosion. The AmB soils on the flatter portion of the site are listed as having
a “slight” erosion hazard. The AgD soils, mapped on the sloping, eastern portion of the site do meet
the “moderate to severe” designation. However, as stated, the eastern slopes were well vegetated,
and we did not observe signs of erosion at the site. Therefore, it is our opinion that while the site
meets the technical definition of an erosion hazard, the site does not have an actual erosion hazard
at the site.
Conventional construction BMP’s should be installed prior to any construction and should
provide adequate erosion control for the disturbed areas of the site. It is critical that the installed
erosion control measures be monitored and maintained, and if necessary modified based on
changing site conditions. In the event that the site is not worked for 7 days or more, the disturbed
areas should be adequately erosion protected and maintained in the event of a significant storm
event. This may include the use of plastic sheeting or mulch. Erosion control should specifically
include the installation of silt fencing along the downslope and side slopes of the active construction
area. Straw waddles and berms may also be necessary. We have not been provided with a copy of
the proposed Temporary Erosion and Sediment Control (TESC) plan at this time. However, provided
standard BMP’s are installed prior to beginning construction, the potential for erosion or sediment
leaving the site should be minimal.
Landslide Hazard Areas per Federal Way Revised Code
The FWRC, Chapter 19.05.070.G(2) defines landslide hazard areas as “those areas potentially
subject to episodic downslope movement of a mass of soil or rock including but not limited to the following
areas.” These are typically characterized as having the following indicators:
a. Any area with a combination of:
i. Slopes greater than 15 percent;
ii. Permeable sediment overlying a relatively impermeable sediment or bedrock;
iii. 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. Any area potentially unstable as a result of rapid stream incision, stream bank erosion or
undercutting by wave action.
d. Any area located in a ravine or on an active alluvial fan, presently or potentially subject to
inundation by debris flows or flooding.
e. Those areas mapped as Class U (unstable), UOS (unstable old slides), and URS (unstable
recent slides) by the Department of Ecology’s Coastal Zone Atlas.
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f. Areas designated as quaternary slumps, earthflows, mudflows, lahars, or landslides on maps
published by the U.S. Geological Survey or Washington State Department of Natural
Resources.
g. Slopes having gradients greater than 80 percent subject to rockfall during seismic shaking
h. Any area with a slope of 40 percent or steeper and with a vertical relief of 10 or more feet
except areas composed of consolidated rock. A slope is delineated by establishing its toe and
top and is measured by averaging the inclination over at least 10 feet of vertical relief.
The east portion of the site contains slopes steeper than 15 percent, however we do not
interpret the site to be underlain by an adverse geologic contact. No seeps or springs were noted on
the slope or on any other portion of the site. No areas on the site were observed or are mapped as
having shown movement during the Holocene epoch or is underlain by mass wastage debris of that
epoch. As stated, the site is not mapped along a shoreline or streambank.
No areas of alluvial fans are mapped nor were any alluvial fans noted in the vicinity of the site
at the time of our past site visits. The site is not covered by the Department of Ecology Coastal Atlas,
however we would interpret the site to be mapped as “stable”. The site’s slopes are not steeper than
80 percent or subject to rock fall during seismic shaking. A portion of the slope on the eastern portion
of the site is steeper than 40 percent with 10 or more feet of vertical relief. However, a retaining wall
will be constructed in this area, effectively eliminating the hazard.
Based on our observations and literature review, the site does have one of the above listed
indicators (areas steeper than 40 percent with 10 or more feet of vertical relief). However, as stated,
a retaining wall will be constructed in this area, and the sl ope was well vegetated at the time of our
site visit. Therefore, no additional buffer for landslide hazard areas should be imposed by the City of
Federal Way.
Seismic Hazards per Federal Way Revised Code
Earthquake-induced geologic hazards per City of Federal Way Revised Code (2016 FWRC),
Chapter 19.05.070.G(3) may include liquefaction, lateral spreading, slope instability, and ground
surface fault rupture. Based on our review of the Liquefaction Susceptibility Map of King County,
Washington (Palmer, et al, 2004), included as Figure 6, the site is within an area mapped as having a
“very low” susceptibility to liquefaction. In our opinion, the potential for liquefaction and lateral
spreading is not significant because of the consolidated nature of the on-site soils.
We also reviewed the Washington State Department of Natural Resources Geologic
Information Portal Fault Hazards map, Figure 7. The Tacoma fault zone is located approximately 675
feet north of the site. No evidence of lateral spreading, slope instability, or ground surface fault
rupture were observed at the site. It is our opinion that provided the proposed development is
adequately designed and constructed, the development should not have any greater seismic risk than
other similarly designed structures in the area.
Seismic Design
The site is located in the Puget Sound region of western Washington, which is seismically
active. Seismicity in this region is attributed primarily to the interaction between the Pacific, Juan de
Fuca and North American plates. The Juan de Fuca plate is subducting beneath the North American
plate at the Cascadia Subduction Zone (CSZ). This produces both intercrustal (between plates) and
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intracrustal (within a plate) earthquakes. In the following sections we discuss the design criteria and
potential hazards associated with the regional seismicity.
Seismic Site Class
Based on our observations and the subsurface units mapped at the site, we interpret the
structural site conditions to correspond to a seismic Site Class “C” for the onsite soils in accordance
with the 2018 IBC (International Building Code) documents and ASCE 7-16 Chapter 20 Table 20.3-1.
This is based on our range of blow counts for the soils encountered at the site. These conditions are
assumed to be representative for the subsurface across the site.
Design Parameters
The U.S. Geological Survey (USGS) completed probabilistic seismic hazard analyses (PSHA) for
the entire country in November 1996, which were updated and republished in 2002 and 2008. W e
used the ATC Hazard by Location website to estimate seismic design parameters at the site. Table 4,
below, summarizes the recommended design parameters.
Peak Ground Acceleration
The mapped peak ground acceleration (PGA) for this site is 0.564g. To account for site class,
the PGA is multiplied by a site amplification factor (FPGA) of 1.2. The resulting site modified peak
ground acceleration (PGAM) is 0.677g. In general, estimating seismic earth pressures (kh) by the
Mononobe-Okabe method are taken as 50 percent of the PGAM, which would be 0.339g.
Foundation Support
Based on the subsurface conditions encountered at our test pit and hand boring locations and
our understanding of the proposed development, we recommend that spread footings bear directly
on the dense native weathered and undisturbed glacial till soils.
Bearing Surface Preparation
The soil at the base of the foundation excavations should be disturbed as little as possible. All
loose, soft, or unsuitable material should be removed. Where materials are over -excavated below a
footing bearing surface, the excavated materials should be replaced with structural fill or controlled
density fill (CDF). Removal of unsuitable soils, if encountered, below the footings should extend
beyond the foundation edges 1 foot horizontally for every 1 foot of vertical excavation. If prepared
bearing surfaces remain open for an extended time, we recommend they be protected by placing a
TABLE 4:
ASCE 7-16 PARAMETERS FOR DESIGN OF SEISMIC STRUCTURES
Spectral Response Acceleration (SRA) and Site Coefficients Short Period
Mapped SRA Ss = 1.334g
Site Coefficients (Site Class C) Fa = 1.200
Maximum Considered Earthquake SRA SMS = 1.601g
Design SRA SDS = 1.068g
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rat slab of CDF or a 4 to 6 inch lift of crushed rock. A representative from our firm should observe the
foundation excavations to determine if suitable bearing surfaces have been prepared.
Spread Footing Design
For the single-family residences, we recommend a minimum width of 24 inches for isolated
footings and at least 16 inches for continuous wall footings. All footing elements should be embedded
at least 18 inches below grade for frost protection. Lateral loads may be resisted by friction on the
base of footings and floor slabs and as passive pressure on the sides of footings. Lateral loads may
be resisted by a combination of base friction and passive pressure against the footings. Spread
footing design parameters are provided in Table 5, below. The bearing capacity provided below
includes a factor of safety of 3.0 and the passive earth pressure includes a factor of safety of 1.5 to
limit lateral deflections. Disturbance of the foundation bearing surface during construction could
result in larger settlements than estimated herein. The allowable bearing value may be increased by
one-third for transient loads such as those induced by seismic events or wind loads. The estimated
settlement is based on typical residential loads.
TABLE 5:
SPREAD FOOTING DESIGN PARAMETERS
Parameter Value FS
Allowable Bearing Pressure (psf) 2,000 3.0
Allowable Coefficient of Friction 0.35 1.5
Allowable Passive Pressure (pcf) 300 1.5
Minimum footing Width – Isolated (inches) 24 --
Minimum footing Width – Strip (inches) 16 --
Estimated Total Settlement (inches) < 1 --
Estimated Differential Settlement Over 50 feet (inches) < ½ --
Floor Slab Support
Slab-on-grade floors, where constructed, should be supported on the still native soils or on
structural fill prepared as described in the “Structural Fill” section of this report. Any areas of old fill
material, if encountered, should be evaluated during grading activity for suitability of structural
support. Areas of significant organic debris should be removed.
We recommend that floor slabs be directly underlain by a minimum of 4-inch-thick pea gravel
or washed 5/8-inch crushed rock and should contain less than 2 percent fines. This layer should be
placed and compacted to an unyielding condition. A synthetic vapor retarder is recommended to
control moisture migration through the slabs. This is of particular importance where moisture
migration through the slab is an issue, such as where adhesives are used to anchor carpet or tile to
the slab.
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A subgrade modulus of 200 pounds per cubic inch 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/Basement Walls
The lateral pressures acting on retaining walls (such as basement or grade separation walls) will
depend upon the nature and density of the soil behind the wall as well as the presence or absence of
hydrostatic pressure. Below we provide recommended design values and drainage recommendations
for retaining walls.
Design Values
For walls backfilled with granular well-drained soil such as gravel backfill for walls or permeable
ballast, we provided the appropriate active and at-rest equivalent fluid pressures in Table 6 below. If
walls taller than 6 feet are required, as seismic surcharge should be included where required by the
code. If walls will be constructed with a backslope and will be braced or otherwise restrained against
movement, we should be notified so that we can evaluate the anticipated conditions and recommend
an appropriate at-rest earth pressure.
TABLE 6:
LATERAL EARTH PRESSURES
Lateral Earth Pressure
Condition, equivalent
fluid density (PCF)
Backfill Material
Gravel backfill for
Walls (WSDOT 9-
03.12(2))
Permeable Ballast
(WSDOT 9-03.9(2))
Native Undisturbed
Glacial Till
At-rest, level backslope 55 45 58
Active, level backslope 35 27 37
Active, 3H:1V backslope 48 32 50
Active, 2H:1V backslope 55 36 57
Seismic Surcharge 15H 11H 16H
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, as described in the “Foundation Support”
section of this report.
Wall Drainage
Adequate drainage behind retaining structures is imperative. Positive drainage which controls
the development of hydrostatic pressure can be accomplished by placing a zone of drainage behind
the walls. Granular drainage material should contain less than 2 percent fines and at least 30 percent
retained on the US No. 4 sieve.
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A minimum 4 inch diameter perforated or slotted PVC pipe should be placed in the drainage
zone along the base and behind the wall to provide an outlet for accumulated water and direct
accumulated water to an appropriate discharge location. We recommend that a nonwoven geotextile
filter fabric be placed between the soil 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.
Typical wall drainage and backfilling details are shown on Figure 8.
A soil 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 soil drainage zone should be compacted to approximately 90 percent of the maximum dry density
(MDD), as determined in accordance with ASTM D1557. Over-compaction should be avoided as this
can lead to excessive lateral pressures on the wall. A geocomposite drain mat may also be used
instead of free draining soils, provided it is installed in accordance with the manufacturer’s
instructions.
Temporary Excavations
All job site safety issues and precautions are the responsibility of the contractor providing
services/work. The following cut/fill slope guidelines are provided for planning purposes only.
Temporary cut slopes will likely be necessary during grading operations or utility installation. 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 including Washingto n
Administrative Code (WAC) and Washington Industrial Safety and Health Administration
(WISHA). Excavation, trenching, and shoring is covered under WAC 296-155 Part N.
Based on WAC 296-155-66401, it is our opinion that the weathered till encountered in our
explorations would be classified as Type C soils and the undisturbed glacial till would be classified as
Type A soils. According to WAC 296-155-66403, for temporary excavations of less than 20 feet in
depth, the side slopes in Type A should be sloped at a maximum inclination of ¾H:1V or flatter from
the toe to top of the slope, and side slopes in Type C soils should have a maximum inclination of
1½H:1V. 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.
Where it is not feasible to slope the site soils back at these inclinations, a retaining structure
should be considered. Retaining structures greater than 4-feet in height (bottom of footing to top of
structure) or that have slopes of greater than 15 percent above them, should be engineered per
Washington Administrative Code (WAC 51-16-080 item 5). 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.
Woldetekle18thAveS.RG
August 28, 2023
page | 13
Site Drainage
All ground surfaces, pavements and sidewalks at the site should be sloped to direct surface
water away from the structures, property lines, and slopes. Surface water runoff should be controlled
by a system of curbs, berms, drainage swales, and or catch basins, and conveyed to an appropriate
discharge point.
We recommend that footing drains are installed for the residence in accordance with IBC
1805.4.2, and basement walls (if utilized) have a wall drain as describe above. The roof drain should not
be connected to the footing drain.
Stormwater Infiltration
The soils at the site consist of weathered glacial till mantling undisturbed glacial till, which is
considered an impermeable surface. Because of the indurate nature of the undisturbed glacial till,
deep infiltration at the site is not feasible.
Low Impact Development (LID) BMPs such as bioretention and/or permeable pavement is not
feasible where the seasonal high groundwater or an underlying impermeable/low permeability layer
(hardpan) would create saturated conditions within 1 foot of the bottom of the lowest gravel base
course. Based on our explorations throughout the project site, permeable pavement could be
considered for this project to help with managing stormwater, provided the proposed bottom of
facility elevations are within the weathered glacial till soils observed in our explorations, and at least
1 foot in elevation higher than the undisturbed glacial till contact.
Design Infiltration Rate for Infiltration Systems & LID BMPs
We completed a soil gradation analysis of a representative sample of the weathered glacial till
soils at test pits TP-3 and TP-5 in accordance with ASTM D6913. For a preliminary design infiltration
rate, we used the Soil Grain Size Method derived from the Massmann equation to determine the
preliminary measured rate of the weathered glacial till soils encountered at the site. We applied
correction factors to the measured infiltration rate in general accordance with the correction factors
presented in the 2021 KCSWDM. The correction factors applied were for test method (0.4 for the Soil
Grain Size Method), facility geometry (0.25) and plugging (0.7). After applying the appropriate
correction factors to the preliminary measured rate, we recommend a design infiltration rate of 0.7
inches per hour be used for infiltration systems and BMPs founded in the weathered glacial till soils
encountered at the site. In-situ infiltration testing in accordance with the 2021 KCSWDM should be
completed once a final location and bottom elevation is determined for any infiltration system.
Construction Considerations
Appropriate design, construction and maintenance measures will be required to ensure the
infiltration rate can be effectively maintained over time. Stormwater Best Management Practices (BMPs)
in accordance with the 2021 KCSWDM should be included in the project plans and specifications to
minimize the potential for fines contamination of Low Impact Development BMPs or infiltration systems
utilized at the site. If an overflow is incorporated into the final design of an infiltration system, we
recommend the overflow be connected to an existing stormwater system or directed to another
discharge point away from any existing or proposed structures.
Suspended solids could clog the underlying soil and reduce the infiltration rate of the facilities.
Additional measures may also be taken during construction to minimize the potential of fines
Woldetekle18thAveS.RG
August 28, 2023
page | 14
contamination of the proposed infiltration system, such as utilizing an alternative storm water
management location during construction or leaving the bottom of the permanent systems 1 to 2 feet
high, and subsequently excavating to the finished grade once the site soils have been stabilized. All
contractors working on the site (builders and subcontractors) should divert sediment laden stormwater
away from proposed infiltration facilities during construction and landscaping activities. No concrete
trucks should be washed or cleaned, and washout areas should not be within the vicinity of the
proposed infiltration facilities.
Permanent Cut and Fill Slopes
Permanent slopes in soil should be no steeper than 2H:1V. Fill slopes constructed on grades
that are steeper than 5H:1V should be constructed in accordance with Appendix J of the 2018 IBC and
should utilize proper keying and benching methods. The benches should be 1½ times the width of
the equipment used for grading and be a maximum of 3 feet in height. Subsurface drainage may be
required in areas where significant seepage is encountered during grading. Collected drainage should
be directed to an appropriate discharge point. Surface drainage should be directed away from all
slope faces.
All permanent slopes should be protected from erosion as soon as feasible after grading is
completed. Typical erosion control methods per the 2021 KCSWDM should be sufficient for proposed
site grading activities. Additionally, permanent slopes should be planted with a hardy vegetative
groundcover, mulched, or armored with quarry spalls as soon as feasible after grading is completed.
EARTHWORK RECOMMENDATIONS
Site Preparation
All structural areas on the site to be graded should be stripped of vegetation, or ganic surface
soils, and other deleterious materials including existing structures, foundations, or abandoned utility
lines. Organic topsoil is not suitable for use as structural fill, but may be used for limited depths in
non-structural areas. Stripping depths ranging from 6 to 30 inches should be expected to remove
these unsuitable soils. Areas of thicker topsoil or organic debris may be encountered in areas of heavy
vegetation or depressions. Although not encountered in our borings, areas of fill material may be
encountered in the footprint of the existing site improvements.
Where placement of fill material is required, the stripped/exposed subgrade areas should be
compacted to a firm and unyielding surface prior to placement of any fill. Excavations for debris
removal should be backfilled with structural fill compacted to the densities described in the
“Structural Fill” section of this report.
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. The
exposed subgrade soil should be proof-rolled with heavy rubber-tired equipment during dry weather
or probed with a 1/2-inch-diameter steel rod during wet weather conditions.
Soft, loose, or otherwise unsuitable areas delineated during proofrolling or probing should be
recompacted, if practical, or over-excavated and replaced with structural fill. The depth and extent of
overexcavation should be evaluated by our field representative at the time of construction. The areas
of old fill material should be evaluated during grading operations to determine if they need mitigation;
recompaction or removal.
Woldetekle18thAveS.RG
August 28, 2023
page | 15
Structural Fill
All material placed as fill for the proposed wall should be placed as structural fill. Material
placed as structural fill should be free of debris, organic matter, trash, and cobbles greater than 4 -
inches in diameter. The moisture content of the fill material should be adjusted as necessary for
proper compaction.
Materials
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 ¾-inch
sieve, such as Gravel Backfill for Walls (WSDOT 9-03.12(2)). If prolonged dry weather prevails during the
wall construction, higher fines content (up to 10 to 12 percent) may be acceptable.
Placement and Compaction
The appropriate lift thickness will depend on the structural fill characteristics and compaction
equipment used, but it is typically limited to 4 to 6 inches for hand operated equipment; thicker lifts
may be appropriate for larger equipment. For larger equipment such as a hoe-pac or drum roller, we
recommend a maximum loose-lift thickness of 12 inches. Structural fill should be compacted to at
least 95 percent of the MDD as determined by the Modified Proctor (ASTM D1557 ). Additionally, the
moisture content should be maintained within 3 percent of the optimum moisture content in
accordance with ASTM D1557.
Suitability of On-Site Materials as Fill
During dry weather construction, the non-organic 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 soil material is over -optimum in moisture content when
excavated, it will be necessary to aerate or dry the soil prior to placement as structural fill.
The weathered and undisturbed glacial till soils are generally comparable to “Common Borrow”
(WSDOT Standard Specification 9-03.14(3)) material and should be suitable for use as structural fill
provided the moisture content is maintained within 2 percent of the optimum moisture level.
We recommend that completed graded-areas be restricted from traffic or protected prior to
wet weather conditions. The graded areas may be protected by paving, placing asphalt-treated base,
a layer of free-draining material such as pit run sand and gravel or clean crushed rock material
containing less than 5 percent fines, or some combination of the above.
Erosion Control
Weathering, erosion and the resulting surficial sloughing and shallow land sliding are natural
processes. 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 reco mmend erosion hazards be
mitigated by applying Best Management Practices (BMPs), as outlined in the 2021 KCSWDM. The
project civil engineer/designer should prepare a drainage and temporary erosion control plan per the
KCSWDM showing which BMPs will be used.
Woldetekle18thAveS.RG
August 28, 2023
page | 16
Temporary erosion control BMPs should be installed at the site prior to the beginning of
clearing, grading, or other construction activities, and should be updated and maintained throughout
construction until final site stabilization is established. Temporary erosion control BMPs may include,
but are not limited to:
• Silt fencing and appropriate soil stockpiling techniques to prevent silty stormwater
from leaving the site,
• Jute matting, hydroseeding, or plastic covering to protect exposed soils,
• Straw wattles, quarry spall armoring, check dams, or other energy attenuation BMPs
to slow the flow of stormwater over slopes and within drainage channels, and,
• Swales and berms to convey construction stormwater away from any slopes.
Erosion protection measures should be in place prior to the start of grading activity on the
site. Where native vegetation is removed because of clearing and grading activities, a dense vegetative
groundcover, grass lawn, or native vegetation should be reestablished as soon as feasible. Permanent
erosion control, such as mulched landscaping areas, groundcovers, hardscaping, or grass lawns,
should be established as soon as feasible once final grades have been completed. All permanent
erosion control methods should be maintained after construction activities have been completed.
LIMITATIONS
We have prepared this report for Asegedom Woldetekle and other members of the permitting
and design team for use in evaluating a portion of this project. Subsurface conditions described
herein are based on our observations of exposed soils on the parcel. This report may be made
available to regulatory agencies or others, but this report and conclusions should not be construed as
a warranty of subsurface conditions. Subsurface conditions can vary over short distances and can
change with time.
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.
◆ ◆ ◆
Woldetekle18thAveS.RG
August 28, 2023
page | 17
We have appreciated the opportunity to be of service to you on this project. If you have any
questions or comments, please do not hesitate to call at your earliest convenience.
Respectfully submitted,
GeoResources, LLC
Davis W. Carlsen, GIT
Senior Staff Geologist
Andrew E. Schnitger, PE Eric W. Heller, PE, LG
Project Engineer Senior Geotechnical Engineer
DC:AES:EWH/dc
DocID: Woldetekle18thAveS.RG
Attachments: Figure 1: Site location Map
Figure 2: Site & Exploration Plan
Figure 3: Site Vicinity Map
Figure 4: NRCS Soils Map
Figure 5: Geologic Map
Figure 6: Liquefaction Susceptibility Map
Figure 7: WA DNR Fault Hazards Map
Figure 8: Typical Wall Drainage & Backfill Detail
Appendix A – Subsurface Explorations
Appendix B – Laboratory Test Results
Approximate Site Location
Figure created from King County iMap website
(https://gismaps.kingcounty.gov/iMap/)
Not to Scale
Site Location Map
Proposed Short Plat
29850 18th Avenue South
Federal Way, Washington
PN: 3674400-155, -160
Doc ID: Woldetekle.18thAveS.F Aug 2023 Figure 1
NOTES:
An excerpt from the ANK Preliminary Short Plat Site Plan by dmp incorporated dated 4/31/2023
Site & Exploration Map
Proposed Short Plat
29850 – 18th Avenue South
Federal Way, Washington
PN: 3674400-155, -160
Doc ID: Woldetekle.18thAveS.F2 August 2023 Figure 2
TP-1
TP-5
TP-4
TP-3
TP-2
Not to Scale
Number and approximate location of test pits (20 11)
Number and approximate location of hand borings (2023)
Approximate Site Location
Figure created from King County iMap website
(https://gismaps.kingcounty.gov/iMap/)
Not to Scale
Site Vicinity Map
Proposed Short Plat
29850 18th Avenue South
Federal Way, Washington
PN: 3674400-155, -160
Doc ID: Woldetekle.18thAveS.F Aug 2023 Figure 3
Approximate Site Location
Figure created from Web Soil Survey
(http://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx)
Soil
Type Soil Name Parent Material Slopes Erosion Hazard Hydrologic
Soils Group
AgC Alderwood gravelly
sandy loam
Glacial drift and/or glacial
outwash over dense
glaciomarine deposits
8 to 15 Moderate
B AgD 15 to 30 Moderate to
severe
AmB Arents, Alderwood
material Basal till 0 to 6 Slight B/D
Not to Scale
NRCS Soils Map
Proposed Short Plat
29850 18th Avenue South
Federal Way, Washington
PN: 3674400-155, -160
Doc ID: Woldetekle.18thAveS.F Aug 2023 Figure 4
Approximate Site Location
An excerpt from the Geologic Map of the Poverty Bay 7.5-Minute Quadrangle, Washington by D. B. Booth, H. H. Waldron, and
K. G. Troost
Symbol Geologic Unit
Qvr Recessional outwash deposits
Qvt Till
Qva Advance outwash deposits
Qpog Glacial deposits of pre-Olympia age
Not to Scale
Geologic Map
Proposed Short Plat
29850 18th Avenue South
Federal Way, Washington
PN: 3674400-155, -160
Doc ID: Woldetekle.18thAveS.F Aug 2023 Figure 5
Qvt
Qpog
Approximate Site Location
An excerpt from the Liquification Susceptibility Map of King County, Washington by Stephen P. Palmer, Sammantha L.
Magsino, Eric L. Bilderback, James L. Poelstra, Derek S. Folger, and Rebecca A. Niggemann (2004)
Not to Scale
Liquefaction Susceptibility Map
Proposed Short Plat
29850 18th Avenue South
Federal Way, Washington
PN: 3674400-155, -160
Doc ID: Woldetekle.18thAveS.F Aug 2023 Figure 6
Approximate Site Location
An excerpt from the Washington State Department of Natural Resources Geologic Information Portal
(https://geologyportal.dnr.wa.gov/)
Not to Scale
Fault Hazards Map
Proposed Short Plat
29850 18th Avenue South
Federal Way, Washington
PN: 3674400-155, -160
Doc ID: Woldetekle.18thAveS.F Aug 2023 Figure 7
Tacoma fault zone (class B)
Notes
Typical Wall Drainage & Backfill
Detail
Proposed Short Plat
29850 18th Avenue South
Federal Way, Washington
PN: 3674400-155, -160
Doc ID: Woldetekle.18thAveS.F Aug 2023 Figure 8
1. Washed pea gravel/crushed rock beneath floor slab could be
hydraulically connected to perimeter/subdrain pipe. Use of 1”
diameter weep holes as shown is one applicable method. Crushed
gravel should consist of 3/4” minus. Washed pea gravel should consist
of 3/8” to No. 8 standard sieve.
2. Wall backfill should meet WSDOT Gravel Backfill for walls Specification
9-03-12(2).
3. Drainage sand and gravel backfill within 18” of wall should be
compacted with hand-operated equipment. Heavy equipment should
not be used for backfill, as such equipment operated near the wall
could increase lateral earth pressures and possibly damage the wall.
The table below presents the drainage sand and gravel gradation.
4. All wall back fill should be placed in layers not exceeding 4” loose
thickness for light equipment and 8” for heavy equipment and should
be densely compacted. Beneath paved or sidewalk areas, compact to
at least 95% Modified Proctor maximum density (ASTM: 01557-70
Method C). In landscaping areas, compact to 90% minimum.
5. Drainage sand and gravel may be replaced with a geocomposite core
sheet drain placed against the wall and connected to the subdrain
pipe. The geocomposite core sheet should have a minimum
transmissivity of 3.0 gallons/minute/foot when tested under a gradient
of 1.0 according to ASTM 04716.
6. The subdrain should consist of 4” diameter (minimum),
slotted or perforated plastic pipe meeting the requirements
of AASHTO M 304; 1/8-inch maximum slot width; 3/16- to 3/8-
inch perforated pipe holes in the lower half of pipe, with
lower third segment unperforated for water flow; tight joints;
sloped at a minimum of 6”/100’ to drain; cleanouts to be
provided at regular intervals.
7. Surround subdrain pipe with 8 inches (minimum) of washed
pea gravel (2” below pipe” or 5/8” minus clean crushed gravel.
Washed pea gravel to be graded from 3/8-inch to No.8
standard sieve.
8. See text for floor slab subgrade preparation.
Materials
Drainage Sand and Gravel ¾” Minus Crushed Gravel
Sieve Size % Passing by
Weight
Sieve Size % Passing by
Weight
¾” 100 ¾” 100
No 4 28 – 56 ½” 75 – 100
No 8 20 – 50 ¼” 0 – 25
No 50 3 – 12 No 100 0 – 2
No 100 0 – 2 (by wet
sieving)
(non-plastic)
Appendix A
Subsurface Explorations
SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GROUP
SYMBOL
GROUP NAME
COARSE
GRAINED
SOILS
GRAVEL CLEAN
GRAVEL
GW WELL-GRADED GRAVEL, FINE TO COARSE GRAVEL
GP POORLY-GRADED GRAVEL
More than 50%
Of Coarse Fraction
Retained on
No. 4 Sieve
GRAVEL
WITH FINES
GM SILTY GRAVEL
GC CLAYEY GRAVEL
More than 50%
Retained on
No. 200 Sieve
SAND CLEAN SAND
SW WELL-GRADED SAND, FINE TO COARSE SAND
SP POORLY-GRADED SAND
More than 50%
Of Coarse Fraction
Passes
No. 4 Sieve
SAND
WITH FINES
SM SILTY SAND
SC CLAYEY SAND
FINE
GRAINED
SOILS
SILT AND CLAY INORGANIC
ML SILT
CL CLAY
Liquid Limit
Less than 50 ORGANIC OL ORGANIC SILT, ORGANIC CLAY
More than 50%
Passes
No. 200 Sieve
SILT AND CLAY INORGANIC
MH SILT OF HIGH PLASTICITY, ELASTIC SILT
CH CLAY OF HIGH PLASTICITY, FAT CLAY
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 D6913. 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.
Unified Soils Classification System
Proposed Short Plat
29850 18th Avenue South
Federal Way, Washington
PN: 3674400-155, -160
Doc ID: Woldetekle.18thAveS.F Aug 2023 Figure A-1
0
1
2
3
4
5
6
475
474
473
472
471
470
469
gravel content
increases
Topsoil
Brown silty SAND (medium dense, moist) (SM) (weathered
glacial till)
Gray silty SAND w/ gravel (dense, moist) (SM) (undisturbed
glacial till)
(Termination Depth - 07/03/2023)
10
8
14
10
17
27
NE
LOG OF BORING HB-1
29850 18th Avenue South, Federal Way
Federal Way WA
1. Refer to log key for definition of symbols, abbreviations, and codes
2. USCS disination is based on visual manual classification
and selected lab testing
3. Groundwater level, if indicated, is for the date shown and may vary
4. NE = Not Encountered
5. ATD = At Time of Drilling
Drilling Company:GeoResources Logged By:KLR
Drilling Method:Hand Auger Drilling Date:07/03/2023
Drilling Rig:Datum:NAVD88
Sampler Type:Porter Sampler Elevation:475'
Hammer Type:Donut Termination Depth:5.5'
Hammer Weight:40lbs Latitude:
Notes:Longitude:
Topsoil Silty sand
Sheet 1 of JOB:Wodletekle.18thAveS FIG.Depth(feet)Elevation (feet)Exploration
notes Soil description
SPT BlowcountsSamplerSymbolTest Results
1020304050Penetration - (blows per foot)
% Water Content
% Fines (<0.075mm)
Plastic Limit Liquid Limit
Groundwater1
0
1
2
3
4
5
6
480
479
478
477
476
475
474
Topsoil
Brown silty SAND w/ gravel (medium dense, moist) (SM)
(weathered glacial till)
Gray silty SAND w/ gravel (dense, moist) (SM) (undisturbed
glacial till)
(Termination Depth - 07/03/2023)
17
16
15
14
27
33
NE
LOG OF BORING HB-2
29850 18th Avenue South, Federal Way
Federal Way WA
1. Refer to log key for definition of symbols, abbreviations, and codes
2. USCS disination is based on visual manual classification
and selected lab testing
3. Groundwater level, if indicated, is for the date shown and may vary
4. NE = Not Encountered
5. ATD = At Time of Drilling
Drilling Company:GeoResources Logged By:KLR
Drilling Method:Hand Auger Drilling Date:07/03/2023
Drilling Rig:Datum:NAVD88
Sampler Type:Porter Sampler Elevation:480'
Hammer Type:Donut Termination Depth:4.5'
Hammer Weight:40lbs Latitude:
Notes:Longitude:
Topsoil Silty sand
Sheet 1 of JOB:Wodletekle.18thAveS FIG.Depth(feet)Elevation (feet)Exploration
notes Soil description
SPT BlowcountsSamplerSymbolTest Results
1020304050Penetration - (blows per foot)
% Water Content
% Fines (<0.075mm)
Plastic Limit Liquid Limit
Groundwater1
Appendix B
Laboratory Test Results
These results are for the exclusive use of the client for whom they were obtained. They apply only to the samples tested and are not indicitive of apparently identical samples.Tested By: Checked By:
Particle Size Distribution Report
PERCENT FINER0
10
20
30
40
50
60
70
80
90
100
GRAIN SIZE - mm.
0.0010.010.1110100
% +3"Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 0.0 23.5 13.7 14.9 21.5 26.46 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200Test Results (ASTM D 6913 & ASTM D 1140)
Opening Percent Spec.*Pass?
Size Finer (Percent)(X=Fail)
Material Description
Atterberg Limits (ASTM D 4318)
Classification
Coefficients
Date Received:Date Tested:
Tested By:
Checked By:
Title:
Date Sampled:Source of Sample: P-1 Depth: 4.5
Sample Number: 4
Client:
Project:
Project No:Figure
Silty SAND with gravel (SM)
.75
.5
0.375
#4
#10
#20
#40
#60
#100
#200
100.0
93.7
90.0
76.5
62.8
54.5
47.9
40.6
33.8
26.4
NP NV NP
SM A-2-4(0)
9.5489 7.1815 1.5557
0.5146 0.1069
Natural Moisture: 6.4%
7/8/23 8/18/23
MAW
AES
PM
7/8/23
Asgedom Woldetekle
Wodletekle.18thAveS
PL=LL=PI=
USCS (D 2487)=AASHTO (M 145)=
D90=D85=D60=
D50=D30=D15=
D10=Cu=Cc=
Remarks
*(no specification provided)
GeoResources, LLC
Fife, WA B-1