20-102489-Geotechnical Report-2020-05-28-V1
Papé Kenworth NW – Federal Way
Proposed Truck Sales and Maintenance Facility
Revised Geotechnical Engineering Report
May 28, 2020
Prepared by:
GeoResources, LLC
4809 Pacific Highway E
Fife, Washington 98424
(253) 896-1011
Prepared for:
Papé Properties
355 Goodpasture Island Rd, Unit 300
Eugene, OR 97401
Attn: Mr. Quinn Closson
Document ID: PapeKenworthNW.FederalWay.RG.rev01
Table of Contents
INTRODUCTION ..................................................................................................................................................... 2
SCOPE ................................................................................................................................................................. 2
SITE CONDITIONS .................................................................................................................................................. 3
Surface Conditions .................................................................................................................................. 3
Site Soils ................................................................................................................................................... 4
Site Geology ............................................................................................................................................ 4
Subsurface Explorations .......................................................................................................................... 4
Subsurface Conditions ............................................................................................................................. 6
Infiltration Testing ................................................................................................................................... 8
Laboratory Testing .................................................................................................................................. 9
Groundwater Conditions ....................................................................................................................... 10
ENGINEERING CONCLUSIONS AND RECOMMENDATIONS ................................................................................. 11
Erosion Hazard Areas ............................................................................................................................ 11
Landslide Hazard Areas ......................................................................................................................... 12
Slope Stability Analysis .......................................................................................................................... 13
Recommended Buffer and Setback from Steep Slopes ........................................................................ 13
Seismic Design ....................................................................................................................................... 14
Foundation Support .............................................................................................................................. 15
Alternative Foundation Support ........................................................................................................... 16
Signal Pole Foundation Support ............................................................................................................ 17
Luminaire Foundation Support ............................................................................................................. 19
Floor Slab Support ................................................................................................................................. 19
Below Grade Walls ................................................................................................................................ 19
Retaining Structures .............................................................................................................................. 20
Below Grade Walls and Retaining Wall Drainage ................................................................................. 22
Temporary Excavations ......................................................................................................................... 23
Site Drainage ......................................................................................................................................... 24
Pavement Section Design ...................................................................................................................... 24
Stormwater Recommendations ............................................................................................................ 28
Detention Pond ..................................................................................................................................... 31
EARTHWORK RECOMMENDATIONS ................................................................................................................... 32
Site Preparation .................................................................................................................................... 32
Structural Fill ......................................................................................................................................... 33
Suitability of On-Site Materials as Structural Fill ................................................................................... 33
Erosion Control ...................................................................................................................................... 34
Wet Weather Earthwork Considerations .............................................................................................. 34
LIMITATIONS ....................................................................................................................................................... 35
Figures
Figure 1: Site Location Map
Figure 2: Site & Exploration Plan
Figure 3: Site Topographic Survey
Figure 4: Site Slopes Map
Figure 5: NRCS Soils Map
Figure 6: Geologic Map
Figure 7: Typical Structural Setback Detail
Figure 8: WA DNR Geologic Hazards Map
Figure 9: Typical MSE Wall Detail
Figure 10: Typical Wall Drainage and Backfill Detail
Figure 11: IBC Keying and Benching
Appendices
Appendix A – Subsurface Explorations
Appendix B – Laboratory Test Results
Appendix C – Global Stability Analyses
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INTRODUCTION
This revised geotechnical engineering report summarizes our site observations, our
subsurface explorations, geotechnical data review and engineering analyses, and provides
geotechnical recommendations and design criteria for the proposed Papé-Kenworth Northwest
truck sales and maintenance facility to be constructed on seven contiguous parcels (PN: 0921049-
028, -139, -140, -160, -187, -206, and -316) located at the northwest corner of South 320th Street and
32nd Avenue South in the Federal Way area of King County, Washington. We understand the parcels
will be annexed to the City of Federal Way during the development; we have therefore addressed
the City development codes in this report. The approximate site location is shown on the Site
Location Map, included as Figure 1.
Revisions to our previous report are bolded and italicized. Our original report was
prepared on March 5, 2020. This revised report addresses the technical review comments from the
City of Federal Way dated April 24, 2020. The City’s comments were provided to us by you on April
27, 2020.
Our understanding of the project is based on our correspondences with you and members
of the design team; our understanding of the City of Federal Way Critical Areas Ordinance and
Development Codes; our review of the Site Plan prepared by H.G. Kimura Architect PLLC dated
March 6, 2020 and the ALTA/NSPS Land Title Survey prepared by Barghausen Consulting Engineers
dated December 7, 2019; and our past experience in the site area. We understand that the site
consists of seven contiguous parcels. Portions of the site are currently developed, including three
single-family residences in the southern portion of the site and a single-family residence, barn, and
horse paddocks in the northern portion of the site. There is also an easement in the southern
portion of the site for a Bonneville Power Administration transmission line, and a delineated wetland
area in the western portion of the site.
We further understand that you propose to develop the site with a new heavy truck
dealership. Based on our project review, the development will include:
An approximate 56,500 square-foot building that will house the showroom, office, shop and
part storage and a detached 14,000 square-foot maintenance shop building. We anticipate
the proposed buildings will be one or two story, wood or steel framed structures founded
on shallow foundations; and that the maintenance facilities will include subgrade walls for
maintenance pits.
Associated parking areas and drive lanes consisting of asphalt concrete pavement (ACP) or
Portland cement concrete (PCC).
Typical underground utilities.
Retaining walls to support fills in the northwestern portion of the project area. The currently
proposed wall configuration consists of three tiered walls with heights of 8 to 14 feet.
A stormwater detention pond in the southwest portion of the project area.
Improvements along the 32nd Avenue South right-of-way, including traffic signal poles at the
intersection of South 320th Street and 32nd Avenue South and luminaires.
Because of the steep slopes in the vicinity of the site, we anticipate that the City of Federal
Way will require a geotechnical engineering report to address the City’s Critical Areas Ordinance per
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the Federal Way Revised Code (FWRC) Chapter 19.145. Our Site & Exploration Plan, attached as
Figure 2, is based on the current proposed site plan dated March 6, 2020 and shows proposed
improvements described above.
SCOPE
The purpose of our services was to evaluate the surface and subsurface conditions across
the site as a basis for providing geotechnical recommendations and conclusions for the proposed
development. 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. Observing subsurface conditions across the site by monitoring the excavation of 16 test pits
at selected locations across the project site;
3. Monitoring the drilling of three hollow-stem auger borings to depths of 21 feet in the
northwest portion of the site using a track mounted drill rig, operated by a licensed driller
and completing the borings as groundwater observation wells;
4. Monitoring groundwater levels within the wells periodically during one wet season
(December 1 – April 30);
5. Monitoring the drilling of two hollow-stem auger borings to depths of 15 feet at the
intersection of South 320th Street and 32nd Avenue South for signal pole and luminaire
foundation design per WSDOT Geotechnical Design Manual;
6. Performing three small scale Pilot Infiltration Tests (PIT) at the approximate bottom elevation
of the proposed infiltration system in accordance with the 2016 King County Surface Water
Design Manual (KCSWDM), as amended by the City;
7. Describing surface and subsurface conditions, including soil type, depth to groundwater, and
an estimate of seasonal high groundwater levels;
8. Addressing the appropriate criteria for geologic hazards per the current City of Federal Way
Critical Areas Ordinance;
9. Providing geotechnical conclusions and recommendations regarding site grading activities
including; site preparation, subgrade preparation, fill placement criteria, suitability of on-site
soils for use as structural fill, temporary and permanent cut and fill slopes, drainage and
erosion control measures;
10. Providing recommendations for seismic design parameters, including 2015 IBC soil profile
type;
11. Providing geotechnical conclusions regarding foundations and floor slab support and design
criteria, including bearing capacity and subgrade modulus as appropriate;
12. Providing recommendations regarding deep foundation elements, as necessary for signage
or canopy foundations;
13. Providing recommendations regarding the traffic signal pole and luminaire foundations and
design criteria;
14. Providing a standard duty and heavy duty hot mix asphalt (HMA) and a heavy duty Portland
cement concrete (PCC) pavement section designs based on traffic data provided by you;
15. Providing our opinion about the feasibility of onsite infiltration including a design infiltration
rate based on our infiltration testing per the 2016 KCSWDM;
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16. Providing conclusions regarding suitable types of retaining walls and soil design parameters
for the walls to be designed by others;
17. Performing slope stability analyses using computer program Slide 2018 by RocScience, in
order to assess the global stability of the existing and proposed conditions at the site,
including the proposed retaining walls and pond embankment;
18. Providing recommendations for erosion and sediment control during wet weather grading
and construction; and,
19. Preparing this written Geotechnical Engineering Report summarizing our site observations and
conclusions, and our geotechnical recommendations and design criteria, along with the
supporting data.
Our original scope of work was summarized in our Proposal for Geotechnical Engineering Services
dated September 26, 2019. We received written authorization to proceed from you on September 27,
2019. Our scope for additional services, including in-situ infiltration testing, borings, and groundwater
monitoring was summarized in our Proposal for Geotechnical Engineering Services dated December 17,
2019, and authorized by you on December 19, 2019.
SITE CONDITIONS
Surface Conditions
As stated, the subject site consists of seven contiguous parcels located northwest of the
intersection of South 320th Street and 32nd Avenue South in the Federal Way area of King County, within
an area of existing commercial and residential development. The site is irregular in shape, measures
approximately 625 to 815 feet wide (east to west) by 1,195 feet deep (north to south), and
encompasses about 21.43 acres The site is bounded by 32nd Avenue South to the east, South 320th
Street to the south, interstate I-5 to the west, and by undeveloped land to the north. The proposed
development is shown on the Site & Exploration Plan, Figure 2, while the existing topography and
site configuration is shown on the Site Topographic Survey, Figure 3. Areas of slopes between 15 to
39 percent and greater than 40 percent are shown on the Site Slopes Map, Figure 4.
Based on review of the King County GIS website, the site can be divided into two topographic
areas: eastern upland and western lowland. The eastern upland is level to gently sloping at 10 to 25
percent. The ground surface between the upland and lowland slopes down to the west, being steepest
in the south with inclinations on the order of 35 to 42 percent with vertical relief of about 45 feet. The
northern portion of this transitional slope is inclined down to the west at about 16 to 24 percent with
vertical relief of 50 feet. The western lowland is generally level to gently sloping. From the toe of the
transitional slope, the ground surface is inclined up to the west at about 10 percent or less. Total
topographic relief across the site is on the order of 70 feet.
The northern parcel is developed with an existing single-family residence, barn, and horse
paddocks. Three of the parcels in the south and southeast portion of the site are developed with
existing single-family residences. Two large transmission line towers are located in the south central
portion of the site. The large center, southwest most, and southeast most parcels of the site are
currently undeveloped.
Vegetation across the undeveloped, western and central portions of the site consists of
moderate to dense stands of deciduous and coniferous trees with a moderate understory of ferns,
blackberries, and other native and invasive shrubs. The transmission line easement is well
vegetated with shrubs and a dense understory of blackberries and other low-growing plants.
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Vegetation near the existing residences generally consists of grasses and typical residential
landscaping. No evidence of erosion or slope movement was observed at the site at the time of our
site visit.
Site Soils
The USDA Natural Resource Conservation Survey (NRCS) Web Soil Survey maps most of the
site, including the areas of proposed development, as being underlain by Alderwood gravelly sandy
loam (AgB, AgC, AgD). An area in the western portion of the site (approximately coincident with the
wetland area) is mapped as being underlain by Seattle Muck (Sk). The Alderwood soils are typically
derived from glacial till or outwash and form on slopes of 0 to 8 (AgB), 8 to 15 (AgC) and 15 to 30 (AgD)
percent. These soils are listed as having a “slight” (AgB), “moderate,” (AgC), and “moderate to severe”
(AgD) erosion hazard when exposed, and are included in hydrologic soils group B. Seattle Muck (Sk) is
derived from grassy organic material, forms on level ground, does not have a listed erosion hazard,
and is included in hydrologic soils group B/D, with the “D” designation typically for the deeper,
unweathered more fine grained deposits. An excerpt from the NRCS soils map for the site area is
included as Figure 5.
Site Geology
The Geologic Map of the Poverty Bay 7.5-Minute Quadrangle, Washington (Booth, Waldron, and
Troost, 2003) maps most of the site and the adjacent areas as being underlain by glacial till (Qvt),
while an area in the western portion of the site is mapped as underlain by wetland deposits (Qw).
The glacial till soils were deposited during the Vashon Stade of the Frasier Glaciation. Glacial till
generally consists of a heterogeneous mixture of gravel, sand, silt, and clay that was deposited at the
base of the advancing continental ice mass, and was subsequently overridden. As such, it is
considered to be over consolidated, and generally has high strength and low compressibility
characteristics where undisturbed. Due to the compact nature and high fines content of glacial till,
the potential for stormwater infiltration is low. Wetland deposits (Qw) are derived from peat and
alluvium deposits and generally consist of pebbly sand or sandy silt that is moderately sorted with
an organic component. These soils are considered to be normally consolidated. Soil deposits with
high fines contents (including peat) generally have moderate to low strength characteristics, and
may exhibit significant settlement over time. No areas of landslide deposits or mass wasting are
mapped within the vicinity of the site. An excerpt of the referenced map is included as Figure 6.
Subsurface Explorations
On October 9, 2019, a field representative from GeoResources, LLC (GeoResources) visited
the site, monitored the excavation of 13 test pits at the site (TP-1 through TP-13), logged the
subsurface conditions encountered in each test pit, and obtained representative soil samples. On
January 7, 2020, a representative from GeoResources returned to the site and monitored the drilling
of five borings to depths of about 15 to 20 feet below the existing ground surface. On January 24,
2020, a representative from GeoResources returned to the site and performed in-situ infiltration
testing and monitored the excavation of three additional test pits (TP-101 through TP-103). The test
pits were excavated by track mounted excavation equipment operated by a licensed earthwork
contractor. The borings were drilled by a licensed drilling contractor operating a truck-mounted drill
rig working under subcontract to GeoResources.
The specific number, locations, and depths of our explorations were selected based on the
configuration of the proposed development, and were adjusted in the field based on consideration
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for underground utilities, existing site conditions, and access limitations. Representative soil
samples obtained from our explorations were placed in sealed plastic bags and then taken to our
laboratory for further examination and testing as deemed necessary.
During drilling, soil samples were obtained at 2½- and 5-foot depth intervals in accordance
with Standard Penetration Test (SPT) as per the test method outlined by ASTM D: 1586. The SPT
method consists of driving a standard 2-inch-diameter split-spoon sampler 18-inches into the soil
with a 140-pound hammer. 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 Standard Penetration Resistance, or “SPT blow count”. The resulting Standard Penetration
Resistance values indicate the relative density of granular soils and the relative consistency of
cohesive soils. Soil densities presented on the test pit logs are based on the difficulty of excavation
and our experience.
The monitoring wells in borings B-1, B-2, and B-3 were installed by inserting closed-end,
screened casing to the target depth. The borings not completed as observation wells (B-4 and B-5)
were backfilled with bentonite chips and abandoned by the driller in accordance with the WAC 173-
160-381. The test pits were backfilled with the excavated soils and bucket tamped, but not
otherwise compacted.
The subsurface explorations completed 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. Based on our experience in
the area and extent of prior explorations in the area, it is our opinion that the soils encountered in
the explorations are generally representative of the soils at the site.
Our test pit, boring, and PIT locations were estimated based on taping and pacing existing
from locatable features. Surface elevations at exploration locations were estimated by interpolating
between contours presented on the 2019 topographic survey. As such, our exploration locations
and elevations should only be considered accurate to the degree implied by our measuring
methods.
The soils encountered were visually classified in accordance with the Unified Soil
Classification System (USCS) and ASTM D: 2488. The USCS is included in Appendix A as Figure A-1.
The approximate locations and numbers of our exploration are shown on the attached Site &
Exploration Plan, Figure 2, while the descriptive logs of our explorations are included in Appendix A
as Figures A-2 through A-11. Table 1, below, summarizes the approximate functional locations,
surface elevations, and termination depths of our subsurface explorations.
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TABLE 1:
APPROXIMATE LOCATIONS, ELEVATIONS, AND DEPTHS OF EXPLORATIONS
Exploration
Number Functional Location
Surface
Elevation1
(feet)
Termination
Depth
(feet)
Termination
Elevation1
(feet)
TP-1
TP-2
TP-3
TP-4
TP-5
TP-6
TP-7
TP-8
TP-9
TP-10
TP-11
TP-12
TP-13
NE portion of site
North center portion of site
NW of proposed shop
West of proposed shop
East of proposed shop
Southern portion of proposed shop
West of proposed showroom
Proposed showroom
East of proposed showroom
West portion of site, N of overhead lines
SW portion of site
Proposed body shop
East portion of site
457
446
440
470
476
481
468
478
484
476
480
486
484
10½
9½
9½
10
7½
9
10
9
6½
9
8½
8½
9
446½
436½
430½
460
468½
472
458
469
477½
467
471½
477½
475
TP-101
TP-102
TP-103
Proposed detention pond
Proposed detention pond
NW portion of site
471
469
446
12
9
9
459
460
437
PIT-1
PIT-2
PIT-3
Northwest portion of site
Northwest portion of site
Northern portion of site
460
442
452
6
6½
10
454
435½
442
B-1 / OW-1
B-2 / OW-2
B-3 / OW-3
B-4
B-5
Northern portion of site
Northern portion of site
Northwest portion of site
Adjacent to 32nd Ave South
Intersection of S 320th St & 32nd Ave S
450
452
451
484
474
21½
20½
21½
15½
15½
428½
431½
429½
468½
458½
Notes: 1 = Elevation datum: NAVD 88 per December 2019 survey by Barghausen Consulting Engineers, Inc
Subsurface Conditions
At the locations explored, we encountered somewhat variable subsurface conditions that
partially differed from the mapped stratigraphy. In general, we encountered surficial materials,
including undocumented fill, overlying glacial till and advance outwash. Table 2, below, summarizes
the approximate thicknesses, depths, and elevations of selected soil layers.
Surficial Materials and Fill
Where encountered, topsoil thicknesses at the locations explored generally ranged between
about 6 and 15 inches. Test pits TP-1, TP-3, and TP-4, in the vicinity of the existing barn did not
encounter a distinct topsoil layer.
Based on our site reconnaissance and subsurface explorations, the area north and west of the
existing barn, including a steep slope with vertical relief of about 12 feet, appears to consist of loose fill
material including manure. This area includes borings B-1 and B-3, which encountered about 7 to 8
feet of loose silty sand that we interpret as fill. Test pit TP-102, in the vicinity of the proposed pond,
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encountered about 3½ feet of silty sand with gravel and scattered construction debris underlying the
topsoil, which we interpret as fill material.
Weathered Soils
Underlying the topsoil and fill, where encountered, we generally observed 1½ to 3 feet of tan to
gray silty sand with variable amounts of gravel in a medium dense, moist condition. We interpret these
soils to be consistent with weathered glacial till and weathered outwash soils. The weathered soils
were not observed in test pit TP-102 and borings B-1 and B-5.
Glacial Till
Underlying the topsoil and weathered soils, 11 of 21 of our explorations in the south and
east portions of the site (upland area) encountered gray silty sand with gravel in a dense to very
dense, moist condition. We interpret these soils to be consistent with undisturbed glacial till. Test
pits TP-5, TP-6, TP-9, TP-11, TP-12, and TP-13 and borings B-4 and B-5 encountered glacial till to the full
depth explored, while test pits TP-2, TP-8, and TP-10 extended through the glacial till into the
underlying advance outwash. A thin (2 to 3 feet thick), discontinuous glacial till layer appears to extend
into the north central portion of the site in the vicinity of test pit TP-2 and PIT-3; this layer was not
encountered in the northeast or northwest portions of the site.
Advance Outwash
Underlying the weathered soils in the north and west portion of the site and the glacial till in
test pits TP-2, TP-8, and TP-10, our explorations encountered brown gravel soils in dense to very dense
condition. We interpret these dense gravelly soils as consistent with advance outwash.
The gravels had variable fines content, as shown in our laboratory test results below. The near
surface soils in the vicinity of the existing barn are classified as silty gravel, with fines contents between
15 and 20 percent. The native gravels north (TP-2) and south (PIT-1) of the existing development had
fines contents of 1.8 to 3.3 percent and the deeper gravel in the vicinity of the development (boring B-
2), had a fines contents of 8.7 percent. As stated above, surficial organic fill material was encountered
in the vicinity of the existing barn and we therefore anticipate that fines have migrated to the
underlying native gravel soils over time.
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TABLE 2:
APPROXIMATE THICKNESS, DEPTHS, AND ELEVATION OF SOIL TYPES ENCOUNTERED IN
EXPLORATIONS
Exploration
Number
Thickness
of Topsoil /
Fill
(feet)
Thickness of
Weathered
Till/Outwash
(feet)
Depth to
Glacial
Till
(feet)
Elevation1 of
Top of
Glacial Till
(feet)
Depth to
Advance
Outwash
(feet)
Elevation1 of
Top of Advance
Outwash
(feet)
TP-1
TP-2
TP-3
TP-4
TP-5
TP-6
TP-7
TP-8
TP-9
TP-10
TP-11
TP-12
TP-13
NE
1¼
NE
NE
½
½
½
½
¾
½
½
1¼
1
2
2¾
2½
2
2½
2½
1½
2
1¾
2½
2½
2¼
2½
NE
4
NE
NE
3
3
NE
2½
2½
3
3
3½
3½
NE
442
NE
NE
473
478
NE
475½
481½
473
477
482½
480½
2
5½
2½
2
NE
NE
2
6
NE
8
NE
NE
NE
455
440½
437½
468
NE
NE
466
472
NE
468
NE
NE
NE
TP-101
TP-102
TP-103
½
4
½
3
NE
1½
NE
NE
NE
NE
NE
NE
3½
4
2
467½
465
444
PIT-1
PIT-2
PIT-3
½
½
2½
1½
2
2
NE
NE
4½
NE
NE
447½
2
2½
7½
458
439½
444½
B-1
B-2
B-3
B-4
B-5
8
NE
7
NE
1
NE
3
2
3
NE
NE
NE
NE
3
1
NE
NE
NE
481
473
8
3
9
NE
NE
442
449
442
NE
NE
Notes: 1 = Elevation datum: NAVD 88 per December 2019 survey by Barghausen Consulting Engineers, Inc
NE = not encountered
Infiltration Testing
On January 24, 2020, a field representative from GeoResources performed three small scale
pilot infiltration tests (PIT), in the northwest portion of the site in the general vicinity of the proposed
infiltration facilities. Infiltration tests PIT-2 and PIT-3 were performed north and west, respectively,
of the proposed facilities because of existing development. Infiltration testing was performed in
general accordance with the 2016 KCSWDM, Reference 6A.
The specific number, location, and depth of our PITs were adjusted in the field based on
consideration for underground utilities, existing site conditions, site access limitations, water access
limitations and encountered stratigraphy. The approximate locations of the infiltration tests are
shown on the attached Site and Exploration Plan, Figure 2. The excavations for the PITs were
excavated by a track-mounted excavator operated by a licensed contractor working for
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GeoResources. The excavations were backfilled with the excavated soils and bucket tamped, but not
otherwise compacted.
TABLE 3:
SMALL-SCALE PIT TEST RESULTS
Infiltration Test
Depth of Testing
Surface
(ft)
Soil Type Surface Area
(ft2)
Measured
Infiltration Rate
(in/hr)
PIT-1 2 SP 25.0 14.5
PIT-2 3 GM 27.5 6.25
PIT-3 8 GM 13.5 6.25
It should be noted that these measured short term infiltration rates only represent the
encountered silty gravel and poorly graded sand with gravel soils. Recommendations regarding the
stormwater infiltration are discussed and included in the “Infiltration Recommendations” section
below.
Laboratory Testing
Geotechnical laboratory tests were performed on select samples retrieved from the test pit
explorations to determine soil index and engineering properties encountered. Laboratory testing
included visual soil classification per ASTM D: 2488, moisture content determinations per ASTM D:
2216, grain size analyses per ASTM D: 6913, modified proctor per ASTM D: 1557, and California
bearing ratio (CBR) test per ASTM D: 1883 standard procedures. The CBR test and the
corresponding modified proctor were performed by an independent analytical laboratory
subcontracted by GeoResources. The results of the laboratory tests are included in Appendix B, and
summarized below in Table 4, below.
TABLE 4:
LABORATORY TEST RESULTS FOR ON-SITE SOILS
Sample Soil Type Lab ID
Number
Gravel
Content
(percent)
Sand
Content
(percent)
Silt/Clay
Content
(percent)
D10
Ratio
(mm)
TP-2, S-1, 6-8’
TP-5, S-1, 5-7’
TP-8, S-2, 7-9‘
TP-13, S-3, 2-4’
Advance Outwash (GP)
Glacial Till (SM)
Advance Outwash (GP-GM)
Weathered Till (SM)
098502
098506
098509
098514
48.8
24.6
49.7
16.7
47.9
42.8
39.8
35.6
3.3
32.6
10.5
47.7
0.2772
<0.074
<0.074
<0.074
B-2, S-1, 5’
B-2, S-2, 20’
Advance Outwash (GM)
Advance Outwash (GW-GM)
099001
099004
43.8
49.5
41.2
41.8
15.0
8.7
<0.074
0.1047
PIT-1, 3’
PIT-2, 3’
Advance Outwash (SP)
Advance Outwash (GM)
099110
099111
46.2
49.6
52.0
30.5
1.8
19.9
0.2920
<0.074
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Groundwater Conditions
Mottling and orange iron-oxide staining was observed as shallow as about 1½ to 2½ feet below
the existing ground surface in the test pits excavated in the south and east portions of the site that are
underlain by glacial till. These characteristics are generally indicative of a seasonal perched
groundwater table, which generally develops when a higher permeability soil is underlain by a lower
permeability soil such as glacial till.
TABLE 5:
APPROXIMATE DEPTHS AND ELEVATIONS OF GROUNDWATER ENCOUNTERED IN
EXPLORATIONS
Exploration
Number
Depth to
Groundwater
(feet)
Elevation of
Groundwater1
(feet)
Date Observed
TP-1 NE NE October 9, 2019 (ATE)
TP-2 NE NE October 9, 2019 (ATE)
TP-3 3½ 436½ October 9, 2019 (ATE)
TP-4 NE NE October 9, 2019 (ATE)
TP-5 NE NE October 9, 2019 (ATE)
TP-6 NE NE October 9, 2019 (ATE)
TP-7 NE NE October 9, 2019 (ATE)
TP-8 NE NE October 9, 2019 (ATE)
TP-9 NE NE October 9, 2019 (ATE)
TP-10 NE NE October 9, 2019 (ATE)
TP-11 NE NE October 9, 2019 (ATE)
TP-12 NE NE October 9, 2019 (ATE)
TP-13 NE NE October 9, 2019 (ATE)
TP-101 7½ 463½ January 24, 2020 (ATE)
TP-102 8½ 460½ January 24, 2020 (ATE)
TP-103 8 438 January 24, 2020 (ATE)
B-1 / OW-1
NE
14
15½
NE
436
434½
January 7, 2020 (ATD)
January 24, 2020
March 5, 2020
B-2 / OW-2
NE
15
17½
NE
437
434½
January 7, 2020 (ATD)
January 24, 2020
March 5, 2020
B-3 / OW-3
18
14½
19
433
436½
432
January 7, 2020 (ATD)
January 24, 2020
March 5, 2020
B-4 NE NE January 7, 2020 (ATD)
B-5 NE NE January 7, 2020 (ATD)
1 = Elevation datum: NAVD 88 per December 2019 survey by Barghausen Consulting Engineers, Inc
ATE = At the time of exploration
ATD = At the time of drilling
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No mottling was observed in the northwest portion of the development underlain by advance
outwash soils. However, groundwater seepage was observed in the north and west portions of the site
in our test pit explorations and standing groundwater was observed in our monitoring wells, as
summarized in Table 5 above. In the northwest portion of the site, a groundwater “peak” was observed
in our observation wells at approximately elevation 436 to 438 feet during our January 24, 2020 site
visit. In the southwest portion of the site, in the vicinity of the proposed pond, groundwater seepage
was observed at approximately elevation 460 to 463 feet. Because we did not observe any seepage
along the face of the site slopes, we anticipate the groundwater surface in the western portion of the
site generally parallels the slope face until reaching the free water surface of the wetlands area at the
toe of the slope. The surface water observed in the wetland at the time of our January 24, 2020 site
visit was at approximately elevation 418 feet.
Based on a review of nearby borings by others and our understanding of regional stratigraphy,
we anticipate the advance outwash is underlain at depth by older pre-Vashon glacial till deposits and
that the observed groundwater is perched within the more permeable outwash soils. We anticipate
fluctuations in the local groundwater levels will occur in response to precipitation patterns, off-site
construction activities, and site utilization.
ENGINEERING 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 the construction of the proposed commercial
development at the site is feasible from a geotechnical standpoint. Provided the geotechnical
recommendations contained in this report are included in the project plans and specifications, the
development will have minimal impact on the steeper slope in the western portion of the site. This
report satisfies the requirements of the FWRC 19.145.250 for a geotechnical engineering report for
potential geologically hazardous areas.
Erosion Hazard Areas
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 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”
As previously stated, the soils mapped in the areas of proposed development are AgB, AgC,
and AgD which have a slight, moderate, and moderate to severe erosion hazards when exposed,
respectively. The AgD soil type is mapped underlying the northwest corner of the proposed
development and underlying the more steeply sloping portion of the site to the west of the
proposed development. In our opinion the potential erosion hazard can be mitigated by installing
conventional construction BMPs prior to beginning construction. Properly installed and maintained
BMPs 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
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specifically include the installation of silt fencing along the downslope and side slopes of the active
construction area. Straw wattles 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
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.
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 site has slopes steeper than 15 percent, but no areas of permeable soils overlying
relatively impermeable soil are mapped or were encountered at the site. No areas of mapped
landslide debris or activity were noted on the published USGS geologic map.
No streams are mapped in the vicinity of the site and the site is not located along a
shoreline. 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 within the area mapped by the Coastal Atlas;
given the slope angles and mapped geology, we would anticipate the eastern portion of the site
would be mapped as stable.
No areas of mass wasting or landslide deposits are mapped at the site by the geologic map
or the Washington DNR Geologic Information Portal. The site slopes are not steeper than 80 percent
and are not subject to rock fall during seismic shaking. Slopes steeper than 40 percent with a
vertical relief of up to 28 feet are identified on the site survey in the southwest portion of the site.
This area is to the west of the southern portion of the proposed project area.
Based on the 2019 site survey, the site has one of the above indicators (slopes steeper than
40 percent with 10 feet or more of vertical relief) and therefore this portion of the project site meets
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the technical definition of landslide hazard area. We did not observe evidence of active or ongoing
movement or slope instability at the time of our site visit. No grading is planned on this portion of
the site. Additionally, our global stability analysis of the slope (described in the “Slope Stability
Analysis” section below) indicates the slope is in a stable condition with factors of safety for static
and dynamic conditions of 2.2 and 1.2, respectively. Based on the results of our slope stability
analyses, the existing slope conditions meet or exceed the minimum factors of safety required by
the City of Federal Way.
Slope Stability Analysis
We performed global stability analyses for static and seismic conditions of both the existing
and proposed slope geometries using cross sections A-A’ and B-B’, as shown on Figure 2. These
cross sections were selected as the most critical sections given the height and steepness of the
slopes, and the proximity of the proposed development. Profile A-A’ was selected based on the
location of the proposed detention pond and profile B-B’ was selected given the anticipated height
of fill required. The slope stability results for the existing and proposed configurations are included
as Appendix C. Seismic loading of 0.26g was added to the stability models based on the peak
ground acceleration with a 2% probability of exceedance within a 50-year period.
We used the computer program SLIDE 2018, from RocScience, to perform the slope stability
analyses. The computer program SLIDE uses a number of methods to estimate the factor of safety
(FS) of the stability of a slope by analyzing the shear and normal forces acting on a series of vertical
“slices” that comprise a failure surface. Each vertical slice is treated as a rigid body; therefore, the
forces and/or moments acting on each slice are assumed to satisfy static equilibrium (i.e., a limit
equilibrium analysis). The FS is defined as the ratio of the forces available to resist movement to the
forces of the driving mass. A FS of 1.0 means that the driving and resisting forces are equal; an FS
less than 1.0 indicates that the driving forces are greater than the resisting forces (indicating failure).
We used the Generalized Limit Equilibrium method using the Morgenstern-Price analysis, which
satisfies both moment and force equilibrium, to search for the location of the most critical failure
surfaces and their corresponding FS. The most critical surfaces are those with the lowest FS for a
given loading condition, and are therefore the most likely to move.
Based on our analyses, the existing and proposed configurations meet static and dynamic
global stability criteria, which requires minimum factors of safety of 1.5 and 1.1, respectively.
Additional discussion of the proposed retaining wall and detention pond configurations is included
in the “Retaining Walls” and “Detention Pond” sections below.
Recommended Buffer and Setback from Steep Slopes
Buffers and setbacks are typically used to protect critical areas from disturbance and also to
protect the proposed development from damage due to the potential hazard. The following
discussions regarding critical area buffers and structure setbacks are based on FWRC Chapter
19.145.230 and IBC 1808.7, respectively.
Buffers typically consist of an undisturbed area of native vegetation, retained or established,
that extend from the edge of the critical area or hazard. The width of the buffer should be a
reflection of the potential hazard and associated risks. Buffer widths are generally measured from
the edge of the critical area being protected, in this case top of slope. Per FWRC 19.145.230,
landslide hazard areas should have a standard buffer of 50-feet, which may be reduced when a
qualified professional demonstrates that the improvements will not increase the slide hazard.
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The area with slopes steeper than 40 percent and more than 10 feet of relief has been
identified on Figure 2. Based on our review of the provided preliminary site plan, we understand
that no structures are currently proposed within 50 feet of the top of th is steep slope. However, the
base of the proposed detention pond embankment is approximately 15 to 30 feet from the top of
the steep slope.
We evaluated the global stability of the existing and proposed site conditions as described
above. Based on our stability analyses, it is our opinion that the proposed improvements will not
create an increased slide hazard and therefore the standard 50-foot buffer required by the City of
Federal Way can be reduced per FWRC 19.145.230.(4). We recommend the buffer be reduced to 15
feet to correspond to the required IBC setback as described below.
A setback is the minimum distance a structure can be placed near a critical area or hazard.
In general, setback distances are greater than buffer widths. The 2015 International Building Code
(IBC), Section 1808.7 requires a building setback from slopes that are steeper than 3H:1V (Horizontal:
Vertical) or 33 percent with greater than 10 feet in vertical height, unless evaluated and reduced
and/or a structural setback is provided by a licensed geotechnical engineer. The setback distance is
calculated based on the vertical height of the slope. The typical 2015 IBC setback from the top of the
slope equals one third the height of the slope or 40 feet, whichever is less, while a setback from the
toe of the slope equals one half the height of the slope or 15 feet, whichever is less.
As stated above, the portion of the ground surface in the southwest portion of the site that
slopes at more than 33 percent has a vertical height of up to 40 feet. Per the 2015 IBC, the minimum
building setback from the top of the slope should be 14 feet. As currently shown on the proposed
site plan, used as basis for Figure 2, the proposed retaining walls, parking areas, and buildings will
meet or exceed this setback distance.
Where the setback from the top of the slope cannot be met, a structural setback may be
used. A structural setback is created by deepening the foundation elements so that, when
measured horizontally from the font of the foundation to the face of the slope, the top of slope
setback discussed above is met. We have provided recommendations for deepened foundations in
the “Foundation Support” section of this report. A typical structural setback diagram is included as
Figure 7.
Seismic Design
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” in accordance with the 2015 IBC
(International Building Code) documents and ASCE 7-10 Chapter 20 Table 20.3-1. This is based on
the SPT (Standard Penetration Test) blow counts recorded during our borings and the anticipated
range of SPT (Standard Penetration Test) blow counts for the soil types observed during test pit
excavation. These conditions were assumed to be representative for the subsurface conditions for
the project site in general.
For design of seismic structures using the IBC 2015, mapped short-period and 1-second
period spectral accelerations, SS and S1, respectively, are required. SS and S1 are for a maximum
considered earthquake, which corresponds to ground motions with a 2 percent probability of
exceedance in 50 years or about a 2,500-year return period (with a deterministic maximum cap in
some regions). 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. We used the ATC Hazard by Location website to estimate seismic design parameters at the site.
Table 6, below, summarizes the recommended design parameters.
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TABLE 6:
2015 IBC PARAMETERS FOR DESIGN OF SEISMIC STRUCTURES
Spectral Response Acceleration (SRA) and Site
Coefficients Short Period 1 Second Period
Mapped SRA Ss = 1.289 S1 = 0.493
Site Coefficients (Site Class C) Fa = 1.000 Fv = 1.307
Maximum Considered Earthquake SRA SMS = 1.289 SM1 = 0.645
Design SRA SDS = 0.859 SD1 = 0.430
Peak Ground Acceleration
The mapped peak ground acceleration (PGA) for this site is 0.522g. To account for site class,
the PGA is multiplied by a site amplification factor (FPGA) of 1.000. The resulting site modified peak
ground acceleration (PGAM) is 0.522g. In general, estimating seismic earth pressures (kh) by the
Mononobe-Okabe method or seismic inputs for slope stability analysis are taken as 30 to 50 percent of
the PGAM, or 0.16g to 0.26g.
Earthquake-Induced Geologic Hazards
Earthquake-induced geologic hazards may include liquefaction, lateral spreading, slope
instability, and ground surface fault rupture. According to the Department of Natural Resources
Geologic Hazards Map, Figure 8, the site is located within the mapped Tacoma Fault Zone. However,
no faults are mapped within 300 feet of the subject site. No evidence of ground fault rupture was
observed in the subsurface exploration or our site reconnaissance. In our opinion, the proposed
development has no greater risk for ground fault rupture than other structures located in this
portion of the Tacoma Fault Zone.
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 dense nature of the glacial till and advance outwash soils
observed on the site, it is our opinion that the risk for liquefaction to occur at this site during an
earthquake is negligible. Provided the design criteria listed below are followed, the proposed
development should have no greater risk of seismic damage than other appropriately designed
structures in the Puget Sound area.
Foundation Support
As stated, we anticipate the proposed structures will be founded on conventional shallow
foundations, while deep foundations such as pin piles or helical anchors may be necessary to
provide additional uplift capacity for proposed signage or canopies. Design criteria and
recommendations for conventional shallow foundations are included in this section. Design criteria
and recommendations for deepened foundations are included in the “Alternative Foundation
Support” section below.
We recommend that spread footings for any new structures be founded on the native glacial
soils or on structural fill that extends to suitable native soils. The soil at the base of the footing
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excavations should be disturbed as little as possible. All loose, soft or unsuitable material should be
removed or recompacted per the “Structural Fill” section of this report.
We recommend a minimum width of 24 inches for isolated footings and at least 18 inches for
continuous wall footings. All footing elements should be embedded at least 18 inches below grade
for frost protection. Footings founded on the properly placed and compacted structural fill or the
shallow weathered glacial soils can be designed using an allowable soil bearing capacity of 2,500 psf
(pounds per square foot) for combined dead and long-term live loads. Footings founded on the
dense glacial till or advance outwash can be designed using an allowable soil bearing capacity of
4,000 psf. The weight of the footing and any overlying backfill may be neglected. The allowable
bearing value may be increased by one-third for transient loads such as those induced by seismic
events or wind loads.
Lateral loads may be resisted by friction on the base of footings and floor slabs and as
passive pressure on the sides of footings. We recommend that an allowable coefficient of friction of
0.35 be used to calculate friction between the concrete and the underlying soil. Passive pressure
may be determined using an allowable equivalent fluid density of 350 pcf (pounds per cubic foot).
Passive resistance from soil should be ignored in the upper 1 foot. Factors of safety have been
applied to these values.
We estimate that settlements of footings designed and constructed as recommended will be
less than 1-inch, for the anticipated load conditions, with differential settlements between
comparably loaded footings of ½-inch or less. Most of the settlements should occur essentially as
loads are being applied. However, disturbance of the foundation subgrade during construction
could result in larger settlements than predicted. We recommend that all foundations be provided
with footing drains in accordance with the 2015 IBC, Section 1805.4.2. We also recommend that a
GeoResources representative evaluate the condition of the exposed subgrade soils prior to setting
the forms and installation of the reinforcing steel.
Alternative Foundation Support
Since uplift capacities for canopies or signs may require greater resistance than can be
provided by conventional shallow foundations, the use of deep foundations such as helical anchors
or reinforced concrete piers may be more appropriate to provide additional uplift capacities while
minimizing the size of the perimeter foundation.
Helical Anchors
Helical anchors (such as the proprietary systems offered by AB Chance and Atlas Systems)
typically consist of a square or circular shaft (1.5-inch square is typical) with and 8 to 12-inch
diameter helix located at the leading edge. The helix is rotated and is advanced into the soil like a
screw, similar to soil augers commonly used for drilling. Depending on the capacity required, one or
more helices may be located along the shaft, typically at about 3-foot intervals. The smallest helix is
the one at the tip of the anchor, with the sizes becoming progressively large at shallower depths.
Helical anchors are screwed into the ground with rotary-type torque motor until refusal
conditions are met. Refusal is typically defined as achieving a specific torque that corresponds to a
specific compressive capacity based on soil conditions and installation equipment used.
Anchors should be spaced a minimum distance of three times the largest helix diameter
measured from the edges of the helices to avoid group effects. The lateral capacity of the battered
piling may be taken as the horizontal vector of the axial pile capacity. The Chance anchor system is a
proprietary system which utilizes helical anchors affixed to a square steel shaft. The uplift capacity
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of the anchor is related to the torsion resistance encountered as the anchor is installed. Torque
monitoring of individual anchors is completed as the anchors are installed using a shear pin that
shears once the design load (torque) is achieved.
The number, size, and spacing of helix plates required to achieve the design loads should be
determined by the anchor contractor and manufacturer using the attached subsurface exploration
logs. We recommend that load testing should be performed in accordance with the Quick Load Test
Method, ASTM D: 1143.
Reinforced Concrete Piers
Alternatively, uplift capacity could be provided by using steel-reinforced concrete piers.
Because of the density of the soils, drilled or augercast concrete piles may be easier to install to the
required depth than helical anchors or driven steel pin piles. We typically recommend that the piers
be a minimum of 12-inches in diameter and be structurally connected to the footing elements.
Where the 12-inch diameter piers bear on dense granular soil, we recommend a preliminary end
bearing value of 4,000 pounds per square foot (psf) and a skin friction value of 1,000 plf. These
values are for piles installed by open-hole techniques. Uplift capacity is generally taken as about 1/2
to 2/3 of allowable pile skin friction resistance (about 500 to 650 plf). Piers of this capacity are
generally acceptable for lightly loaded structures. The concrete piers are usually short and are
analyzed as rigid bodies with respect to lateral design. The short concrete piers are usually installed
with a “highway” auger or similar truck mounted drill rig. On steeply sloping sites, or for deeper
piers, a larger crane type mounted drill rig is required. This may also require a large bench
excavation in order to provide the drill rig access to the pier locations. This recommended capacity
is based on a minimum penetration equal to a minimum of 5 feet into suitable bearing soils that
were encountered at about 2 to 4 feet below the existing ground surface. Minimum embedment
depths will depend on finish floor elevations. Once the site plan is finalized, we can review
minimum embedment depths. The piers are typically placed on 4 to 6 foot centers starting at the
corners of the individual shallow foundation elements. Piers with center-to-center spacing less than
3 pile diameters may need to account for group effects.
Signal Pole Foundation Support
We understand that existing signal poles at the intersection of South 320th Street and 32nd
Avenue South may be relocated as part of the proposed development. Standard foundation depths
range from 6 to 20 feet, depending on the foundation type, the pole class, resultant horizontal
tension, and the soil conditions. Table 7 below presents the recommended minimum foundation
depths for various factors, based on WSDOT design criteria, for Type IV and V strain pole
foundations.
Because of the proximity of the anticipated pole location to an existing slope, the foundation
depth may need to be extended. For slopes flatter than 3H:1V no adjustment is necessary. For
poles located on slopes inclined at 3H:1V, the foundations depths should be extended 0.5B, where
“B” is the foundation diameter. For poles located on slopes inclined at 1.5H:1V the foundations
depths should be extended 1.0B. Interpolation of foundation depths between indicated slope
inclinations is permitted.
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TABLE 7:
RECOMMENDED MINIMUM DRILLED PIER DEPTHS FOR SIGNAL POLE FOUNDATIONS
Allowable
Lateral
Bearing
Pressure
Drilled Pier
Diameter
“B”
(feet)
Pole Class – Resultant Horizontal Tension1 (lbs)
1900 2700 3700 4800 5600 6300 7200
Drilled Pier Depth (feet) on Level Ground2
1,000 psf to
1,500 psf
3
4
11
10
13
11
15
13
16
15
18
15
19
16
20
18
1,500 psf to
2,500 psf
3
4
9
8
11
9
12
10
14
12
15
13
15
13
16
14
>2,500 psf 3
4
7
6
8
7
9
8
10
9
11
10
12
10
13
11
Corrugated Metal Pipe Depth (feet) on Level Ground2
1,000 psf to
1,500 psf
3
4
11
10
13
11
15
13
16
15
18
15
19
16
20
18
1,500 psf to
2,500 psf
3
4
9
8
11
9
12
10
14
12
15
13
15
13
16
14
> 2,500 psf 3
4
7
6
8
7
9
8
10
9
11
10
12
10
13
10
Ref: Design Manual – Type IV and V Strain Pole Traffic Signal Foundation, Standard Plan J-27.10-01
Notes:
1 For actual resultant horizontal tension factors between the design values shown, use the next higher value.
2 For 2H:1V ground slopes add 0.5B to depth; For 1.5H:1V ground slopes add 1.0B to depth. Interpolation between these values
is permitted. Signal pole foundations should not be placed on slopes steeper than 1.5H:1V
We understand the signal pole northwest of the intersection will be located in the general
vicinity of boring B-5. At the location of boring B-5, very dense glacial till with blow counts greater
than 50 blows per foot (bpf) was encountered at about 2 feet below the ground surface
(approximately elevation 472 feet). The very dense glacial till was mantled by dense crushed
surfacing rock in the existing driveway. Correlations between SPT blow count and lateral bearing
pressure are provided in Table 17-2 of the WSDOT Geotechnical Design Manual (Foundation Design for
Signals Signs, Noise Barriers, Culverts, and Buildings, M 46-03.8, dated October 2013). Using the blow
count data from boring B-5, all foundation embedment depths greater than 5 feet will have an
allowable lateral bearing pressure in excess of 4,500 psf. Therefore, in our opinion, the signal pole
foundation may be sized using Table 7, above, using the row of design values for allowable lateral
bearing pressure greater than 2,500 psf.
Once the signal pole class and location for proposed signal poles have been selected, we can
provide additional comments on the required minimum embedment depth. Based on our
explorations, we anticipate that the foundation holes can be drilled with a conventional auger. The
drilling or excavation contractor should realize that differing soil conditions might be encountered at
the specific pole locations. Because of the proximity of existing underground utilities, careful utility
locating will be required before the foundations are installed.
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Luminaire Foundation Support
We understand that luminaires are proposed along the 32nd Avenue South right-of-way as
part of the proposed development. The WSDOT standard design for luminaire foundations is shown
on WSDOT Standard Plan J-28.30-03. Foundation Type A has a minimum embedment depth of 4.5
feet on ground surfaces inclined at 4H:1V or less and a minimum allowable lateral bearing pressure
of 2,000 psf. Foundation Type B has a minimum embedment depth of 8 feet on slopes inclined
steeper than 4H:1V, but not exceeding 2H:1V, and an allowable lateral bearing capacity of 1,500 psf.
Luminaires founded in the dense to very dense glacial till encountered in borings B-4 and B-
5 may be designed using Foundation Type A or B. All loose, soft or unsuitable material should be
removed or recompacted per the “Structural Fill” section of this report.
Luminaires founded in structural fill placed as described in the “Structural Fill” section may
also be designed using Foundation Type A or B. We understand that only minor amounts of grading
are proposed along the 32nd Avenue South right-of-way and therefore anticipate the proposed
luminaires will be founded in native glacial till soils.
Floor Slab Support
We anticipate that the proposed buildings may include slab-on-grade floors that should be
supported on the native soils or on structural fill prepared as described below. Although not
encountered in our explorations in the vicinity of the proposed buildings, any areas of old fill
material should be evaluated during grading activity for suitability of structural support. Areas of
significant organic debris should be removed as described in accordance with the “Site
Preparation” section of this report.
We recommend that floor slabs be directly underlain by a minimum 4-inch thick pea gravel
or clean crushed rock with less than 2 percent fines. This layer should be placed in one lift 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 th e slab is underlain
by silty till soils or where moisture migration through the slab is an issue, such as where adhesives
are used to anchor carpet or tile to the slab.
A subgrade modulus of 250 pci (pounds per cubic inch) may be used for subgrades prepared
as recommended. We estimate that settlement of the floor slabs designed and constructed as
recommended, will be ½ inch or less over a span of 50 feet.
Below Grade Walls
We do not expect the buildings will have basements, but subgrade walls could be
constructed in association with maintenance pits. The lateral pressures acting on below grade walls
will depend upon the nature and density of the soil behind the walls. It is also dependent upon the
presence or absence of hydrostatic pressure. If the walls are backfilled with granular well-drained
soil, the design active pressure may be taken as 35 pounds per cubic foot (pcf) (equivalent fluid
density). For subgrade walls that are restrained from deflection, an at-rest pressure of 55 pcf may
be used. These design values assume a level backslope and drained conditions as described below.
Where required by code, a seismic surcharge of 10H is recommended for active conditions, calculated
using the Mononobe-Okabe method. This surcharge is in addition to the static lateral earth pressure
and should be assumed to have resultant at 2/3H, and assumes the wall will be backfilled with
adequately compacted structural fill.
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Lateral loads may be resisted by friction on the base of wall footings and as passive pressure
on the sides of footings and the embedded portion of the wall, as described in the “Foundation
Support” section.
Retaining Structures
Retaining walls are proposed to support fills along the western and northwest portion of the
project area and provide up to 41 feet of grade separation. Per the FWRC 19.120.120, walls for
commercial developments are limited to six feet in height, and rockeries and retaining walls visible
from a public right-of-way shall be composed of rock, brick, or other textured/patterned wall styles as
approved by the City. We understand you are requesting a deviation to construct retaining walls up to
about 14 feet in height. The proposed configuration provides up to 41 feet of grade separation and
consists of three tiered walls with individual maximum heights of 10 to 14 feet that are horizontally
separated by terraces sloping at up to 3H:1V. While not currently proposed, we anticipate additional
shorter retaining walls may be required to support cuts in the southeastern portion of the project
area.
Where the proposed parking lot will be within 1H:1V from the base of the proposed retaining
walls, we recommend a live load surcharge of 250 psf be applied to model traffic loading. As proposed,
the building is sufficient setback so that it will not impose a surcharge on the walls.
We recommend the following geotechnical design parameters be used for the design of
retaining walls:
TABLE 8:
RECOMMENDED SOIL PROPERTIES OF ON-SITE SOILS FOR WALL DESIGN
Soil Type
Moist Unit
Weight
(pcf)
Cohesion1
(psf)
Phi
(degrees)
Equivalent
Fluid Pressure
(pcf)
Weathered Till/Outwash (medium dense)
Gravelly Advance Outwash (dense)
Glacial Till (dense)
Structural Fill (Common Borrow)
125
135
138
130
0
0
500
0
34
42
38
35
35
27
33
35
Notes: 1Cohesion should only be used to model foundation soil, not retained soil
Mechanically Stabilized Earth Walls
Mechanically stabilized earth (MSE) walls are constructed using compacted soil with layers of
reinforcing material, such as geosynthetics or steel strips, that extend behind the wall face to create
a reinforced soil mass. Detailed wall design should be performed by the wall designer, including
internal and external stability, sliding resistance, and required reinforcement layout and properties.
Wall backfill should consist of structural fill and should be compacted to 95% of the maximum dry
density (MDD) as determined by the Modified Proctor (ASTM D: 1557). The soil drainage zone within
12- to 18-inches of the wall should be compacted to approximately 90 percent of the MDD.
Typical facings for MSE walls with geogrid or geotextile reinforcement are small modular
concrete blocks (such as Cornerstone, Keystone, and others) or large modular concrete blocks (such
as Redi-rock, Ultrawall, and others). As stated above, rockeries may be considered for use as a
decorative facing in front of wrapped face geosynthetic MSE walls. In our opinion, MSE walls with
steel reinforcement (or gabion style wall) such as the Hilfiker wall systems, would also be feasible
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from a geotechnical perspective, however the wall facing may not meet the City style requirements
described above.
Grid lengths for wall under 6 feet in height are typically on the order of 0.7H, where H is the
total height of the wall. Grid lengths for walls over 6 feet are typically on the order of 1.1H. Greater
lengths may be required for tiered wall configurations when the upper wall surcharges the lower
wall, typically when the upper wall is located within 1H:1V from the base of the lower wall. Our
recommended grid lengths for the proposed configuration are described below in the ”Preliminary
Global Stability Analysis” section. A typical detail for a tiered MSE retaining wall constructed
using small concrete block facing and geogrid reinforcement is included as Figure 9.
Rockeries
Rockeries should not be used unless the retained material would be stable without the rock
facing. Rockeries are considered to act principally as erosion protection and they are not considered
to provide strength to the slope unless designed as a buttress using limit equilibrium slope stability
methods. Based on our review of the subsurface explorations and the proposed plans, it is our
opinion that cuts in the southeast portion of the site will likely encounter dense glacial till which has
historically been shown to be stable with rockery facings at minimal heights. We do not recommend
rockeries be constructed in front of fill with more than 3 feet of exposed height, such as the
proposed fills in the western portion of the project area, unless constructed as a wrapped-face MSE
wall with rockery facing.
We recommend tiered rockeries be separated by level terraces at least equal to the height of
the lower rockery, so that the upper rockery does not place a surcharge load on the lower rockery.
Proposed rockeries should be constructed in accordance with the ARC Rock Wall Construction
Guidelines.
Gravity Walls
Large modular concrete block walls (such as Redi-Rock or Ultrawall) may also be feasible if
designed as gravity walls (without geosynthetic reinforcement). Gravity walls depend primarily on
the weight of the concrete blocks to resist failure from overturning and sliding. Taller wall sections
and walls subject to surcharge loading (including tiered wall configurations with less than 1H:1V
separation) will require larger block sizes to resist the forces acting on the wall. Gravity walls
constructed using Redi-Rock or Ultrawall blocks are typically feasible up to heights of about 12 feet,
where no surcharge loads are applied.
Preliminary Global Stability Analysis
We analyzed the global stability of the proposed tiered wall configurations along cross-
section B-B’ as shown on Figure 2. We understand the proposed configuration consists of 3 tiered
walls with exposed heights of up to 14 feet with up to 3H:1V slopes between the walls. Our global
stability model assumed a total vertical separation of 41 feet from the base of the lower wall to the
top of the upper wall, consisting of two 11 foot tall walls (lower and middle walls), one 9 foot tall
wall (upper wall), and two terraces each with a horizontal distance of 15 feet and vertical height of
5 feet (3H:1V slope).
Our results indicate the lower walls should have a minimum reinforcement length of 1.8H
and the upper wall should have a minimum reinforcement length of 1.0H, where H is the total height
of the MSE wall (including embedment). These recommended reinforcement lengths would meet
static and dynamic global stability criteria, which requires minimum factors of safety of 1.5 and 1.1,
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respectively. We did not perform detailed internal, external, or compound stability analyses of the
proposed walls. We recommend the wall designer be required to perform these analyses and to
determine the required reinforcing strengths, lengths, and spacing where MSE walls are used. The
actual design length of reinforcement may be controlled by internal or external stability
considerations and may be greater.
TABLE 9:
RETAINING WALLS GLOBAL STABILITY ANALYSES RESULTS
Cross Section Condition Loading Condition Factor of Safety
B-B’
Existing Static
Dynamic
3.3
1.5
Proposed Static
Dynamic
1.8
1.2
Based on the measured infiltration rates in the advance outwash, we do not anticipate
significant mounding will occur below the proposed infiltration trenches. However, to account for
potential local groundwater mounding and the corresponding impact to global stability, our model
for the proposed developed conditions includes a water table elevated by 3 to 4 feet below the
proposed infiltration trenches.
The proposed walls at the site should be constructed with adequate drainage, as described
below, to reduce the development of hydrostatic pressure acting on the proposed retaining walls.
Our stability analyses assumed saturated conditions would not develop in the reinforced zones of
the proposed MSE walls.
Below Grade Walls and Retaining Wall Drainage
Adequate drainage behind subgrade walls and 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 greater than the US No. 4 sieve.
A soil drainage zone should extend horizontally at least 18 inches from the back of the wall
or back of reinforced zone. 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 MDD. Over-compaction should be avoided as this can lead to excessive lateral
pressures. A geocomposite drain mat may also be used instead of free draining soils, provided it is
installed in accordance with the manufacturer’s instructions. Typical wall drainage and backfill is
shown on Figure 10.
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.
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Tiered MSE Retaining Wall Drainage
Where tiered MSE walls are constructed, we recommend a minimum 4-inch diameter
perforated or slotted PVC collector pipe should be placed at the back of the reinforcement zone at
the base of the wall as shown on Figure 9. The collector pipe should be surrounded by ¾ inch to 1½
inch washed gravel and wrapped in filter fabric. The drain should run the entire length of the wall
and have proper outlets to an approved discharge point at the ends and/or at regularly spaced
points along the wall. Solid pipe should be used for outlets through the face or under the retaining
wall, and should be connected to the perforated collector pipe.
Potential additional drainage requirements, such as blanket and chimney drains, should be
determined by the wall designer based on the final wall design.
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 Washington
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 glacial till deposits would be
classified as Type A soils, and the advance outwash and weathered glacial deposits would be
classified as Type B soils, except where seepage occurs and would then be classified as Type C.
Existing fill soils encountered at the site should also be classified as Type C.
According to WAC 296-155-66403, for temporary excavations of less than 20 feet in depth,
the side slopes in Type C soils should be sloped at a maximum inclination of 1.5H:1V or flatter from
the toe to top of the slope, the side slopes in Type B soils should be sloped at a maximum inclination
of 1H:1V or flatter, and side slopes in Type A soils should be laid back at a slope inclination of
0.75H:1V or flatter. 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
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.
Permanent Cut and Fill Slopes
We recommend a maximum slope of 2H:1V (Horizontal:Vertical) for permanent cut slopes
and for fill slopes up to 6 feet in height. Fill slopes taller than 6 feet should be sloped at 3H:1V per
FWRC 19.120.100. Where slopes are not feasible, retaining structures as discussed above should be
considered.
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Fill slopes constructed on grades that are steeper than 5H:1V should be constructed in
accordance with Appendix J of the 2015 IBC and the King County Surface Water Design Manual, as
amended by the City of Federal Way and FWRC Title 16, as well as Chapter 16.142. Fill slopes should
utilize proper keying and benching methods. An excerpt from the 2015 IBC, Appendix J is included
as Figure 11. 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 2016 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.
Site Drainage
All ground surfaces, pavements and sidewalks at the site should be sloped to direct surface
water away from the structures. 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.
Collected water should not be discharged onto slopes steeper than 30 percent.
We recommend that footing drains are installed for the buildings in accordance with 2015 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.
Pavement Section Design
We understand that several pavement sections may be used for the onsite portion of the
development, including flexible pavement design consisting of hot mix asphalt (HMA) in the
passenger car parking stalls, passenger car drive lanes, and either HMA or rigid pavement design
consisting of Portland cement concrete (PCC) in the truck traffic areas. We were provided with a
draft Memorandum prepared by Transportation Engineering Northwest (TENW) dated October 8,
2019 which provided estimates of weekday peak hour traffic at the proposed facility.
Pavement Subgrades
Pavement subgrade areas should be prepared by removing any soft or deleterious material
down to firm and unyielding soils in accordance with the “Site Preparation” section of this report.
The prepared subgrade should be evaluated by proof-rolling with a fully-loaded dump truck or
equivalent heavy point load equipment. Soft, loose, or wet areas that are identified should be
recompacted or removed, as appropriate. Over-excavated areas should be backfilled with
compacted structural fill. Where fill is placed, the upper 2 feet of roadway subgrade should have a
maximum dry density of at least 95 percent of the MDD, as determined in accordance with the ASTM
D: 1557.
On-Site Pavement Sections
We have prepared this analysis in accordance with the 1993 AASHTO flexible and rigid
pavement design methods. The AASHTO 93 design method quantifies traffic loading in terms of 18-
Kip ESALs (equivalent single axle loads). The estimated ESALs over the entire design life were
determined using the provided traffic data and assumed vehicle loads, and extending the daily value
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over a 20- or 40-year design life. We have assumed that commercial truck traffic will drive across the
heavy HMA and PCC pavement sections, while the parking stall and light HMA pavement sections will
only be used by passenger cars and occasional delivery trucks. We assumed that each passenger
car applies an average of 0.008 ESALs. We assumed that commercial trucks would apply 1.2 ESALs.
Based on our bearing ratio (CBR) test results, we have assumed an equivalent subgrade modulus
value of 8 ksi. These assumptions should be verified prior to construction, and, if the assumptions
contained herein are not correct, we should be notified and allowed to review our calculations.
Table 10, below, summarizes our assumptions and inputs for the design of the pavement
sections, and Table 11, below, summarizes the recommended pavement section thicknesses.
TABLE 10:
INPUT DATA FOR PAVEMENT DESIGN
Parameter Parking
Stalls HMA Light HMA Heavy HMA PCC
Design Life (years) 20 20 20 40
Design Traffic Load (ESALs) 3,504 162,644 525,600 1,051,200
Initial Serviceability 4.2 4.2 4.2 4.5
Terminal Serviceability 2.3 2.3 2.3 2.5
Reliability, R 85% 85% 85% 80%
Elastic Modulus, E (ksi) N/A N/A N/A 4,000
Modulus of Subgrade Reaction, k (pci) N/A N/A N/A 200
Resilient Modulus, Base Course (ksi) 28 28 28 N/A
Resilient Modulus, Subgrade (ksi) 8 8 11 N/A
Layer Coefficient, HMA (a1) 0.44 0.44 0.44 N/A
Layer Coefficient Base Course (a2) 0.13 0.13 0.13 N/A
Drainage Coefficient (m, Cd) 1 1 1 1
Notes: ESALs – Equivalent Single Axle Loads
ksi – kips per square inch
pci – pounds per cubic inch
TABLE 11:
SECTION THICKNESS RECOMMENDATIONS
Section Parking Stalls
(inches)
Light HMA
(inches)
Heavy HMA
(inches)
PCC
(inches)
Pavement 2 3.5 4.5 6.5
CSBC or CSTC 4 7 7.5 N/A1
Notes: CSBC – Crushed Surface Base Course per WSDOT 9-03.9(3)
CSTC – Crushed Surface Top Course per WSDOT 9-03.9(3)
1 Leveling course as needed below PCC (typically about 2- to 4-inches of crushed rock)
The above recommended section thicknesses meet the AASHTO 93 design standards based
on the assumed traffic loading. Additional loading may contribute to premature failure of the
pavement section. We anticipate heavy vehicle traffic from construction traffic or emergency
vehicles would likely exceed the design loading of the parking stall HMA section.
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Off-Site Pavement Sections
We have also prepared pavement sections in accordance with the 1993 AASHTO flexible and
rigid pavement design methods for 32nd Avenue South. Based on the City of Federal Way
Comprehensive Plan, Map III-4 we understand 32nd Avenue South is considered a minor arterial
with street section type “K”. Per the City’s Minimum Street Design Standards, Table 1 street
section “K” has an average daily traffic of 5,000 to 15,000.
No off-site traffic data was provided. We assumed an initial average daily traffic value of
15,000, equal to the maximum value for a street section type “K”. We as sumed 2% annual traffic
growth. Based on traffic count information retrieved from the WSDOT Traffic GeoPortal website
for Highway 509 (a street section type “K” roadway in the City of Federal Way), we assumed the
following traffic percentages: 96.75% passenger cars, 2.5% single-unit trucks, and 0.75% multi-unit
trucks. We assumed that each passenger car applies an average of 0.008 ESALs, the single-unit
trucks would apply 1.8 ESALs (HS-20 loading), and the multi-unit trucks would apply 3 ESALs. These
assumptions should be verified prior to construction, and, if the assumptions contained herein are
not correct, we should be notified and allowed to review and update our calculations, as
appropriate.
Table 12, below, summarizes our assumptions and inputs for the design of the pavement
sections, and Table 13, below, summarizes the design pavement section thicknesses.
TABLE 12:
INPUT DATA FOR PAVEMENT DESIGN
Parameter HMA PCC
Design Life (years) 20 40
Design Traffic Load (ESALs) 10,621,154 25,791,510
Initial Serviceability 4.2 4.5
Terminal Serviceability 2.3 2.5
Reliability, R 85% 80%
Elastic Modulus, E (ksi) N/A 4,000
Modulus of Subgrade Reaction, k (pci) N/A 200
Resilient Modulus, Base Course (ksi) 28 N/A
Resilient Modulus, Subgrade (ksi) 9 N/A
Layer Coefficient, HMA (a1) 0.44 N/A
Layer Coefficient Base Course (a2) 0.13 N/A
Drainage Coefficient (m, Cd) 1 1
Notes: ESALs – Equivalent Single Axle Loads
ksi – kips per square inch
pci – pounds per cubic inch
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TABLE 13:
32nd AVENUE SOUTH DESIGN SECTION THICKNESS
Section HMA
(inches)
PCC
(inches)
Pavement 7 11
CSBC or CSTC 11 N/A1
Notes: CSBC – Crushed Surface Base Course per WSDOT 9-03.9(3)
CSTC – Crushed Surface Top Course per WSDOT 9-03.9(3)
1 Leveling course as needed below PCC (typically about 2- to 4-inches of crushed rock)
While our calculations indicate the above HMA section would support the assumed traffic
loading, per the City Public Works drawing number 3-2K, the minimum HMA pavement sections for
a minor arterial street section type “K” consist of the below options.
TABLE 14:
MINIMUM PAVEMENT SECTION, TYPE K, MINOR ARTERIAL
Section (inches) (inches)
HMA ½-inch 8 10
HMA 1-inch 6 N/A
CSTC N/A 10
Notes: CSTC – Crushed Surface Top Course per WSDOT 9-03.9(3)
In our opinion, either minimum pavement section is suitable for 32nd Avenue South. We
recommend a total crushed rock base course thickness of 11-inches, consisting of either CSTC or
CSBC, be placed below HMA pavement sections.
Pavement Frost Conditions
Frost-susceptible soil is generally regarded as having greater than 3 percent finer than
0.02 millimeter (mm). Soil with a fines content not exceeding 7 percent passing the No. 200 sieve,
based on the minus ¾-inch fraction, can normally be expected to have 3 percent or less finer than
0.02 mm. Based on the soils observed during our construction monitoring, most of the near-surface
soils could be considered frost-susceptible. Based on information provided in the WSDOT Pavement
Policy, we recommend assuming the frost depth would be about 18 inches. For both rigid and
flexible pavements, WSDOT recommends that the total depth of the pavement section be at least 50
percent of the frost depth. The recommended parking stall HMA pavement section is less than 9-
inches thick and therefore may be susceptible to frost heave damage; a thicker CSBC base layer
could be used with our recommended parking stall HMA pavement section to provide frost
protection, or additional maintenance should be anticipated.
Pavement Materials and Construction
In general, the aggregate base course, HMA, and PCC should be constructed in accordance
with WSDOT Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT Standard
Specifications, 2016). HMA should conform to Section 5-04 in the WSDOT Standard Specifications and
the PCC should conform to Section 5-05 of the WSDOT Standard Specifications. We recommend that
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crushed rock used as CSBC in pavement sections consist of material of approximately the same
quality as “crushed surfacing (base course)” (or better) described in Section 9-03.9(3) of the WSDOT
Standard Specifications. We further recommend that CSBC material be compacted to at least 95
percent of the MDD based on the modified Proctor procedure (ASTM D: 1577).
Stormwater Recommendations
We understand that the City of Federal Way uses the 2016 King County Surface Water Design
Manual (KCSWDM) for stormwater management. Stormwater facilities should be designed and
constructed in accordance with the 2016 KCSWDM. All infeasibility criteria and minimum setbacks
should be considered prior to the selection of a stormwater management method. Infiltration
facilities should not be located within 200 feet of a steep slope hazard area, defined in the 2016
KCSWDM as an area on a slope of 40 percent inclination or more with a vertical elevation change of
at least 10 feet. Therefore, infiltration facilities should not be located within 200 feet of the top of
the steep slope as shown on Figure 2 in the southwest portion of the site. Based on the current site
plans, we understand no infiltration facilities are proposed within 200 feet of the steep slope.
In accordance with Section 5.2 of the 2016 KCSWDM, a minimum separation of 3 feet
between the bottom of an infiltration facility and the top of a seasonal high groundwater table or
other impermeable layer is required. Per the 2016 KCSWDM, evidence of seasonal high
groundwater includes mottling or iron oxide staining.
In our opinion, the minimum separation requirements for infiltration facilities can be met
where advance outwash was encountered, including in the vicinity of test pits TP-1, TP-2, TP-3, TP-4, TP-
7, and TP-103 and borings B-1, B-2, and B-3 in the western portion of the project area. Where glacial till
was encountered mantling advance outwash, including test pits TP-8 and TP-10, infiltration should be
feasible if the bottom elevation of the facility is located within the gravelly outwash soils. Therefore, it
is our opinion that onsite infiltration is feasible for the proposed development if the facilities are
located in the vicinities of test pits TP-1, TP-2, TP-3, TP-4, TP-7, TP-8, TP-10, or TP-103 provided the
minimum vertical separation requirements can be achieved through design. Our groundwater
monitoring measured groundwater at approximately elevation 463 feet in the northwest portion of
the site.
Our test pit explorations in the south and east portions of the site, in the vicinity of test pits
TP-5, TP-6, TP-9, TP-11, TP-12, and TP-13 and borings B-4 and B-5 encountered glacial till to the full
depth explored with evidence of seasonal groundwater as shallow as 2 feet below the existing
ground surface. The minimum required vertical separation between the bottom of an infiltration
facility and evidence of seasonal high groundwater likely cannot be met in these portions of the site.
Therefore, it is our opinion that onsite infiltration in the vicinity of test pits TP-5, TP-6, TP-9, TP-11, TP-
12, and TP-13 is not feasible.
Additionally, onsite infiltration should not occur within fill material unless the fill is placed and
compacted under the supervision of a geotechnical engineer and the fill has a minimum measured
infiltration rate of 8 inches per hour. As noted, we understand you propose to fill the western portion
of the project site. We do not recommend infiltration facilities have bottom elevations located within
the fill, unless it meets the above requirements. Materials such as Permeable Ballast (WSDOT Spec 9-
03.9(2)) or Gravel Backfill for Drains (WSDOT Spec 9-03.12(4)) can provide the required infiltration rate.
Design Infiltration Rate
We performed three small scale pilot infiltration tests (PIT-1, PIT-2, and PIT-3) in general
accordance with the 2016 KCSWDM. No indicators of an impermeable layer underlying the test
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locations pits were observed during over-excavation. Based on our test results, we recommend
allowable long-term design infiltration rates of 2.75 inches per hour be used to design infiltration
facilities within the silty gravel soils in the vicinity of PIT-2, PIT-3, TP-3, B-1, B-2, and B-3 (north and
west of the existing barn); and a design infiltration rate of 6.5 inches per hour be used to design
infiltration facilities within the poorly graded gravel and poorly graded sand soils in the vicinity of
PIT-1, TP-4, TP-7, TP-8, and TP-103 (southwest of the existing barn). The recommended infiltration
rates and locations are summarized below in Table 15.
TABLE 15:
RECOMMENDED DESIGN INFILTRATION RATE OF ON-SITE SOILS
Infiltration Rate
(in/hr) Soil Type Location
Approximate Depths
Encountered
(ft)
2.75 GM / GW-GM
PIT-2
PIT-3
TP-3
B-1
B-2
B-3
2 – 7+
7 – 10+
2½ - 9½+
8 – 21+
4 – 21+
9 – 21+
6.5 GP / SP
PIT-1
TP-4
TP-7
TP-8
TP-103
1½ - 6+
2 – 10+
2 – 10+
6 – 9+
2 – 9+
We recommend that a representative from our firm be onsite at the time of excavation of the
proposed infiltration facilities to verify that the soils encountered during construction are consistent
with the soils observed in our subsurface explorations.
The design infiltration rate is determined based on the procedure provided in section 5.2.1
of the 2016 KCSWDM. Three correction factors are applied to account for testing (Ftesting), geometry
(Fgeometry), and plugging (Fplugging). The design infiltration rate is determined as follows:
Idesign = Imeasured X Ftesting X Fgeometry X Fplugging
Where:
Idesign = Infiltration rate to be used for design of infiltration facility
Imeasured = Infiltration rate measured in the field or estimated by grain size analysis
Ftesting = Accounts for test method used (0.4 to 0.75)
Test Method Correction Factor (Ftesting)
Large Scale PIT 0.50
Small Scale PIT 0.50
Single Ring Percolation Test 0.30
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Fgeometry = Accounts for the influence of facility geometry and depth to water table or other
impervious strata. Fgeometry must be between 0.25 and 1.0 and is determined by:
Fgeometry = 4 D/W + 0.05
Where:
D = depth from the bottom of the proposed facility to the nearest impervious layer.
W = Width of Facility
Fplugging accounts for reductions in infiltration rates over the long term due to plugging of soils.
Soil Type Correction Factor (Fplugging)
Loams and sandy loams 0.7
Fine sands and loamy sands 0.8
Medium sands 0.9
Coarse sands or cobbles 1.0
Based on the definitions and criteria outlined above, for infiltration rates determined by the
small scale PIT method, we used a value of 0.5 for Ftesting, a value of 1.0 for Fgeometry, and a value of 0.9
for Fplugging.
Permeable Pavement
Per 2016 KCSWDM, Section C.2.7, permeable pavement is not feasible where the seasonal high
ground water 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 the soils
encountered in our test pits, it is our opinion that permeable pavement is feasible at the site provided
the vertical separation can be met and maintained after site grading. Where the upper weathered till
soils are proposed to be removed during grading, we anticipate the vertical separation from seasonal
high groundwater cannot be met. We recommend we be on site to observe the vertical separation to
the undisturbed glacial till near the central and southeast portions of the site if permeable pavement is
proposed to be used in those areas.
Based on a soil gradation analysis performed in accordance with ASTM D: 6913, where
infiltration is feasible, we recommend a preliminary long-term design infiltration rate of 0.5 inches per
hour in the medium dense tan silty sand with gravel soils generally encountered at depths of 0.5 to 2.5
feet across the site. Once the final permeable pavement section design is determined, the City of
Federal Way will likely require in-situ infiltration performance testing be performed to verify the
design infiltration rate in accordance with the 2016 KCSWDM.
Treatment Capacity
Cat-ion exchange capacity (CEC) and organic content testing were also performed on four
samples by an independent laboratory to evaluate the treatment capacity of the shallow onsite soils
for LID methods. The results of the laboratory tests are included in Appendix B and summarized in
Table 16 below. The shallow onsite soils in the vicinity of both the proposed parking areas (TP-4
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and TP-11) and the proposed infiltration trenches (TP-3 and TP-11) meet treatment requirements
per the KCSWDM.
TABLE 16:
TREATMENT CAPACITY OF ON-SITE SOILS
Location Sample Lab ID
Number
Cation Exchange
Capacity
(mEq/100g)
Organic Content
(percent)
Minimum Requirement for Treatment 5.0 1.0
Proposed infiltration trench TP-3, S-1
TP-7, S-1
098503
098507
23.8
11.3
2.4
3.0
Proposed paved area TP-4, S-1
TP-11, S-1
098505
098511
11.5
8.53
3.5
3.2
Construction Considerations
Suspended solids could clog the underlying soil and reduce the infiltration rate. To reduce
potential clogging of the infiltration systems, the infiltration system should not be connected to the
stormwater runoff system until after construction is complete and the site area is landscaped, paved or
otherwise protected. Additional measures may also be taken during construction to minimize the
potential of fines 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. After construction activities have been
completed, periodic sweeping of the paved areas will help extend the life of the infiltration system.
Detention Pond
A stormwater detention pond is currently proposed to be located in the southwest portion
of the site. As currently designed, the pond will have a constructed embankment on the downhill
(western) side and a cut slope on the uphill (eastern) side, as shown on the attached site plan. We
recommend that the fill portion of the embankment (the downhill, western portion of the
embankment) be constructed by excavating a keyway at the bottom of the berm, per section 5.1.1.1
of the KCSWDM. We recommend the keyway be at least 5 feet wide at the bottom and the side
slopes should be no steeper than 1H:1V. The keyway should extend into the native soils a minimum
of 4 feet. The keyway should reduce ground water seepage along the embankment/native soil
contact. The minimum 5-foot width may require the use of small compaction equipment, such as a
hoe-pack. The contractor may opt to widen the keyway in order to use a wheel roller.
All material placed as fill for the pond embankment should be placed as structural fill.
Structural fill in the embankment should be compacted to at least 95 percent of MDD (maximum dry
density as determined in accordance with ASTM D: 1557) and be at or slightly over the optimum
moisture content. Per the KCSWDM, structural fill material placed for construction of the
embankment shall have a fines content between 20 and 60 percent, and a maximum of 60 percent
sand. We also recommend the structural fill contain less than 30 percent gravel. Based on our grain
PapeKenworthNW.FederalWay.RG.rev01.kss
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size analyses, the native glacial till soils located at the site generally meet these gradation
requirements.
The surface of the fill embankment should be protected from erosion by covering it with a
minimum of 3 inches of 1¼-inch compacted crushed rock. The crushed rock should be underlain by
Mirafi 140N non-woven geotextile or approved equivalent. Preventing erosion on the embankment
slopes is paramount to the long-term stability, performance, and level of required maintenance of
the pond embankment.
We recommend that the proposed pond be lined with a low permeability liner to reduce
infiltration and reduce seepage from occurring below the downslope embankment. We anticipate
the bottom of the proposed pond will encounter silty gravel soil that may have a moderate
infiltration rate. The pond should not be designed to use infiltration, because of the proximity to the
adjacent steep slope. The native glacial till soils encountered in the upland portion of the site
generally meet the requirements of section 6.2.4.1 of the KCSWDM and in our opinion are suitable
for re-use as a compacted till liner. The compacted till liner should be compacted to at least 95
percent of MDD and be 18 inches after compaction. Alternatively, a geosynthetic pond liner, such as
PVC or HDPE, may be installed along the pond and the pond embankment to prevent excessive
seepage and saturation of soils.
We recommend that a representative from GeoResources should be present during
construction to verify conditions as they are exposed and to verify that the fill and pond are
constructed per the approved plan and recommendations contained herein.
Slope Stability
Based on our slope stability analyses, the proposed pond embankments meet or exceed a
FS of 1.5 and a FS of 1.1 in static and seismic conditions, respectively, provided our
recommendations are incorporated into the project design and construction. Details of the slope
stability analyses are included in Appendix C and a summary of the results is provided in Table 17
below.
TABLE 17:
POND EMBANKMENT SLOPE STABILITY ANALYSES RESULTS
Cross Section Water Condition Loading Condition Factor of Safety
A-A’
Full
Full
Emptied (Rapid Drawdown)
Static
Dynamic
Static
2.0
1.1
2.0
As stated above in the “Recommended Buffer and Setback from Steep Slopes” section,
because our stability analyses indicate the proposed improvements will not create an increased
slide hazard, we recommend the buffer above the steep slope be reduced to 15 feet. We
understand the base of the proposed detention pond embankment is approximately 15 to 30 feet
from the top of the steep slope, meeting or exceeding our recommended buffer.
EARTHWORK RECOMMENDATIONS
Site Preparation
All structural areas on the site to be graded should be stripped of vegetation, organic surface
soils, and other deleterious materials including existing structures, foundations or abandoned utility
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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 about 6 to 18 inches should be expected to
remove these unsuitable soils in the undeveloped areas of the site. Areas of thicker topsoil or
organic debris may be encountered in areas of heavy vegetation or depressions.
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 over excavation 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.
Structural Fill
All material placed as fill associated with mass grading, as utility trench backfill, pond
embankment, under building areas, or under roadways and pavement areas should be placed as
structural fill. The structural fill should be placed in horizontal lifts of appropriate thickness to allow
adequate and uniform compaction of each lift. Structural fill should be compacted to at least 95
percent of MDD (maximum dry density) as determined in accordance with ASTM D: 1557.
The appropriate lift thickness will depend on the structural fill characteristics and
compaction equipment used. We recommend that the appropriate lift thickness be evaluated by
our field representative during construction. We recommend that our representative be present
during site grading activities to observe the work and perform field density tests.
The suitability of material for use as structural fill will depend on the gradation and moisture
content of the soil. As the amount of fines (material passing US No. 200 sieve) increases, soil
becomes increasingly sensitive to small changes in moisture content and adequate compaction
becomes more difficult to achieve. During wet weather, we recommend use of well-graded sand
and gravel with less than 5 percent (by weight) passing the US No. 200 sieve based on that fraction
passing the ¾-inch sieve, such as Gravel Backfill for Walls (WSDOT 9-03.12(2)). If prolonged dry
weather prevails during the earthwork and foundation installation phase of construction, higher
fines content (up to 10 to 12 percent) may be acceptable. Requirements for pond embankment fill
are discussed in the “Detention Pond” section of this report.
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.
Suitability of On-Site Materials as Structural Fill
During dry weather construction, any nonorganic onsite 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 moisture content of the soil is over optimum when
excavated, it will be necessary to aerate or dry the soil prior to placement as structural fill.
PapeKenworthNW.FederalWay.RG.rev01.kss
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The native weathered till and glacial till soils generally consisted of silty sand with gravel.
These soils are generally comparable to common borrow (WSDOT 9-03.14(3)) and are suitable for
use as structural fill provided the moisture content is maintained within 2 percent of the optimum
moisture level. However, these soils may become difficult to adequately compact during extended
periods of wet weather or where seepage occurs. As stated, the native glacial till generally meets
gradation requirements for use in detention pond embankments and as a compacted till liner per
the 2016 KCSWDM.
The native advance outwash soils generally consist of poorly-graded gravel with variable
amounts of silt. These soils are generally comparable to select borrow (WSDOT 9-03.14(2)) and are
suitable for use as structural fill provided the moisture content is maintained within 3 percent of the
optimum moisture level. The upper advance outwash soils in the vicinity of the existing barn in the
northwest portion of the site had a higher fines content (about 15 to 20 percent), and are generally
comparable to common borrow.
The undocumented fill soils encountered northwest of the existing barn appear to contain a
significant amount of organic content and we do not recommend these soils be re-used as structural
fill. The undocumented fill soil encountered in test pit TP-102 in the southwest portion of the site
appeared to consist of reworked native soils, and should be suitable for re-use as structural fill
provided any encountered debris is removed.
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 recommend erosion protection
measures will need to be in place prior to grading activity on the site. Erosion hazards can be
mitigated by applying BMPs outlined in the 2016 King County Surface Water Design Manual.
Wet Weather Earthwork Considerations
In the Puget Sound area, wet weather generally begins about mid-October and continues
through about May, although rainy periods could occur at any time of year. Therefore, it is strongly
encouraged that earthwork be scheduled during the dry weather months of June through
September. Most of the soil at the site contains sufficient fines and is highly susceptible to changes
in water content and tends to become unstable and impossible to proof-roll and compact if the
moisture content exceeds the optimum.
In addition, during wet weather months, the groundwater levels could increase, resulting in
seepage into site excavations. Performing earthwork during dry weather would reduce these
problems and costs associated with rainwater, construction traffic, and handling of wet soil.
However, should wet weather/wet condition earthwork be unavoidable, the following
recommendations are provided:
Grading and earthwork should not be accomplished during periods of heavy, continuous
rainfall.
PapeKenworthNW.FederalWay.RG.rev01.kss
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The ground surface in and surrounding the construction area should be sloped as much as
possible to promote runoff of precipitation away from work areas and to prevent ponding of
water.
Work areas or slopes should be covered with plastic when not being worked. The use of
sloping, ditching, sumps, dewatering, and other measures should be employed as necessary
to permit proper completion of the work.
Earthwork should be accomplished in small sections to minimize exposure to wet conditions.
That is, each section should be small enough so that the removal of unsuitable soils and
placement and compaction of clean structural fill could be accomplished on the same day.
The size of construction equipment may have to be limited to prevent soil disturbance. It
may be necessary to excavate soils with a backhoe, or equivalent, and locate them so that
equipment does not pass over the excavated area. Thus, subgrade disturbance caused by
equipment traffic would be minimized.
Fill material should consist of clean, well-graded, sand and gravel, of which not more than 5
percent fines by dry weight passes the No. 200 mesh sieve, based on wet-sieving the fraction
passing the ¾-inch mesh sieve. The gravel content should range from between 20 and 50
percent retained on a No. 4 mesh sieve. The fines should be non-plastic.
No exposed soil should be left uncompacted and exposed to moisture. A smooth-drum
vibratory roller, or equivalent, should roll the surface to seal out as much water as possible.
In-place soil or fill soil that becomes wet and unstable and/or too wet to suitably compact
should be removed and replaced with clean, granular soil (see gradation requirements
above).
Excavation and placement of structural fill material should be observed on a full-time basis
by a geotechnical engineer (or representative) experienced in wet weather/wet condition
earthwork to determine that all work is being accomplished in accordance with the project
specifications and our recommendations.
We recommend that the above requirements for wet weather/wet condition earthwork be
incorporated into the contract specifications, where applicable.
LIMITATIONS
We have prepared this report for use by the Papé Group, Cobalt Development, Barghausen
Engineering, H.G. Kimura Architect, Soundview Consultants, and other members of the design team,
for use in the design of a portion of this project. The data used in preparing this report and this
report should be provided to prospective contractors for their bidding or estimating purposes only.
Our report, conclusions and interpretations are based on our site reconnaissance, subsurface
explorations, and data from others, and should not be construed as a warranty of the subsurface
conditions.
Variations in subsurface conditions are possible between the explorations and may also occur
with time. A contingency for unanticipated conditions should be included in the budget and schedule.
Sufficient monitoring, testing and consultation should be provided by our firm during construction to
confirm that the conditions encountered are consistent with those indicated by the explorations, to
provide recommendations for design changes should the conditions revealed during the work differ
from those anticipated, and to evaluate whether earthwork and foundation installation activities
comply with contract plans and specifications.
PapeKenworthNW.FederalWay.RG.rev01.kss
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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.
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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
Neil A. Ferguson, PE
Project Geotechnical Engineer
Keith S. Schembs, LEG Eric W. Heller, PE, LG
Principal Senior Geotechnical Engineer
NAF:EWH:KSS/naf
Doc ID: PapeKenworthNW.FederalWay.RG.rev01
5/30/2020
Approximate Site Location
(Map created from King County Public GIS http://gismaps.kingcounty.gov/iMap/)
Not to Scale
Site Location Map
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F May 2020 Figure 1
Preliminary Site Plan prepared by H.G. Kimura Architect , LLC dated May 18, 2020
Approximate Test Pit Location Global Stability Cross-section
Approximate Boring Location Geologically Hazardous Area Buffer (15 feet)
Scale
1” = 100’
Site & Exploration Plan
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc: PapeKenworthNW.FederalWay.F May 2020 Figure 2
TP-1
TP-2
TP-3
TP-4
TP-5
TP-7
TP-8
TP-6
TP-9
TP-10
TP-11
TP-13
TP-12
A
A’
B
TP-101 TP-103
B-1
B-2
B-3
B-5
B-4
PIT-1
PIT-2
PIT-3
B’
Geologically Hazardous Area
TP-102
ALTA/NSPS Land Title Survey prepared by Barghausen Consulting Engineers, Inc dated December 7, 2019
Not to Scale
Site Topographic Survey
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc: PapeKenworthNW.FederalWay.F May 2020 Figure 3
ALTA/NSPS Land Title Survey prepared by Barghausen Consulting Engineers, Inc dated December 7, 2019
15 to 39 percent slope
40 percent or greater slope
Not to Scale
Site Slopes Map
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc: PapeKenworthNW.FederalWay.F May 2020 Figure 4
Approximate Site Location
(Map created from NRCS Web Soil Survey)
Soil
Type Soil Name Parent Material Slopes Erosion
Hazard
Hydrologic
Soils Group
AgB
Alderwood Gravelly
Sandy Loam Glacial till and/or glacial outwash
0 – 6 Slight B
AgC 6 – 15 Moderate B
AgD 15 – 30 Moderate
to Severe B
Sk Seattle Muck Grassy organic material Level None B/D
W Water - - - -
Not to Scale
NRCS Soils Map
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F May 2020 Figure 5
Approximate Site Location
An excerpt from the Geologic Map of the Poverty Bay 7.5-Minute Quadrangle, Washington, By Derek B. Booth, Howard H.
Waldron, and Kathy G. Troost (2003)
Qvt Glacial Till
Qw Wetland deposits
Not to Scale
Geologic Map
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F May 2020 Figure 6
Conventional Footing
Footing Extension
Typical Structural Setback Detail
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F May 2020 Figure 7
Setback Distance
Slopes Greater
Than 30 Percent
Foundation
Element
Residential
Structure
Footing
Extension
Slopes Greater
Than 30 Percent
Setback Distance
Foundation
Element
Residential
Structure
Approximate Site Location
Map created from Washington DNR Geologic Information Portal
(https://geologyportal.dnr.wa.gov/)
Not to Scale
WA DNR Natural Hazards Map
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F May 2020 Figure 8
Tacoma Fault Zone
Notes
Typical Wall Drainage and Backfill Detail
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F May 2020 Figure 10
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)
IBC Keying and Benching
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F May 2020 Figure 11
Appendix A
Subsurface Exploration
SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GROUP
SYMBOL
GROUP NAME
COARSE
GRAINED
SOILS
More than 50%
Retained on
No. 200 Sieve
GRAVEL
More than 50%
Of Coarse Fraction
Retained on
No. 4 Sieve
CLEAN
GRAVEL
GW
WELL-GRADED GRAVEL, FINE TO COARSE GRAVEL
GP
POORLY-GRADED GRAVEL
GRAVEL
WITH FINES
GM
SILTY GRAVEL
GC
CLAYEY GRAVEL
SAND
More than 50%
Of Coarse Fraction
Passes
No. 4 Sieve
CLEAN SAND
SW
WELL-GRADED SAND, FINE TO COARSE SAND
SP
POORLY-GRADED SAND
SAND
WITH FINES
SM
SILTY SAND
SC
CLAYEY SAND
FINE
GRAINED
SOILS
More than 50%
Passes
No. 200 Sieve
SILT AND CLAY
Liquid Limit
Less than 50
INORGANIC
ML
SILT
CL
CLAY
ORGANIC
OL
ORGANIC SILT, ORGANIC CLAY
SILT AND CLAY
Liquid Limit
50 or more
INORGANIC
MH
SILT OF HIGH PLASTICITY, ELASTIC SILT
CH
CLAY OF HIGH PLASTICITY, FAT CLAY
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.
Unified Soil Classification System
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F May 2020 Figure A-1
Test Pit TP-1
Location: Northeast portion of site
Approximate Elevation: 457’
Depth (ft) Soil Type Soil Description
0 - 2 SM Tan silty SAND with some gravel and small roots (medium dense, moist) (weathered
outwash)
2 - 10½ GP Tan poorly-graded GRAVEL with sand, grades to very dense and lightly cemented below
9.5 feet (dense, moist) (advance outwash)
Terminated at 10½ feet below ground surface.
No mottling observed.
No caving observed.
No groundwater seepage observed.
Test Pit TP-2
Location: Northwest portion of site
Approximate Elevation: 446’
Depth (ft) Soil Type Soil Description
0 - 1¼ - Topsoil/rootzone
1¼ - 4 SM Tan silty SAND with some gravel (medium dense, moist) (weathered outwash)
4 - 5½ SM Gray silty SAND with gravel, moderately cemented (dense, moist) (glacial till)
5½ - 9½ GP Tan to brown poorly-graded GRAVEL with sand, trace silt (dense, moist) (advance
outwash)
Terminated at 9½ feet below ground surface.
No mottling observed.
No caving observed.
No groundwater seepage observed.
Logged by: NAF Excavated on: October 9, 2019
Test Pit Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-2
Test Pit TP-3
Location: Northwest of proposed shop
Approximate Elevation: 440’
Depth (ft) Soil Type Soil Description
0 - 2½ SM Tan to dark brown silty SAND with some gravel (medium dense, moist) (weathered
outwash)
2½ - 6½ GP-GM Dark brown poorly-graded GRAVEL with silt and sand (medium dense to dense, moist to
wet) (advance outwash?)
6½ - 9½ GM Tan silty GRAVEL with sand (medium dense to dense, moist) (advance outwash?)
Terminated at 9½ feet below ground surface.
No mottling observed.
Moderate caving observed below 3 feet.
Groundwater seepage observed from 3½ to 5 feet bgs.
Test Pit TP-4
Location: West of proposed shop
Approximate Elevation: 470’
Depth (ft) Soil Type Soil Description
0 - 2 SM Tan silty SAND with some gravel and small roots (medium dense, moist) (weathered
outwash)
2 - 10 GP Brown poorly-graded GRAVEL with sand (dense, moist) (advance outwash)
Terminated at 10 feet below ground surface.
No mottling observed.
No caving observed.
No groundwater seepage observed.
Logged by: NAF Excavated on: October 9, 2019
Test Pit Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-3
Test Pit TP-5
Location: East of proposed shop
Approximate Elevation: 476’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 3 SM Tan silty SAND with gravel, mottled at bottom contact (medium dense, moist) (weathered
till)
3 - 7½ SM Gray silty SAND with gravel, moderately cemented (dense to very dense, moist) (glacial
till)
Terminated at 7½ feet below ground surface.
Mottling observed from 2½ to 3 feet bgs.
No caving observed.
No groundwater seepage observed.
Test Pit TP-6
Location: Southern portion of proposed shop
Approximate Elevation: 481’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 3 SM Tan to mottled gray silty SAND with gravel (medium dense, moist) (weathered till)
3 - 9 SM Gray silty SAND with gravel, moderately cemented (dense to very dense, moist) (glacial
till)
Terminated at 9½ feet below ground surface.
Mottling observed from 2 to 3 feet bgs.
No caving observed.
No groundwater seepage observed.
Logged by: NAF Excavated on: October 9, 2019
Test Pit Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-4
Test Pit TP-7
Location: West of proposed showroom
Approximate Elevation: 468’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 2 SM Tan silty SAND with some gravel and small roots (medium dense, moist) (weathered
outwash)
2 - 10 GP Brown poorly-graded GRAVEL with sand (dense, moist) (advance outwash)
Terminated at 10 feet below ground surface.
No mottling observed.
No caving observed.
No groundwater seepage observed.
Test Pit TP-8
Location: Proposed showroom
Approximate Elevation: 478’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 2½ SM Tan silty SAND with gravel, mottled at bottom contact (medium dense, moist) (weathered
till)
2½ - 6 SM Gray silty SAND with gravel, moderately cemented (dense to very dense, moist) (glacial
till)
6 - 9 GP-GM Brown poorly-graded GRAVEL with silt and sand (dense, moist) (advance outwash)
Terminated at 9 feet below ground surface.
Mottling observed from 2 to 2½ feet bgs.
No caving observed.
No groundwater seepage observed.
Logged by: NAF Excavated on: October 9, 2019
Test Pit Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-5
Test Pit TP-9
Location: East of proposed showroom
Approximate Elevation: 484’
Depth (ft) Soil Type Soil Description
0 - ¾ - Topsoil/rootzone
¾ - 2½ SM Tan to mottled gray silty SAND with gravel (medium dense, moist) (weathered till)
2½ - 6½ SM Gray silty SAND with gravel, moderately cemented (very dense, moist) (glacial till)
Terminated at 6½ feet below ground surface.
Mottling observed from 1½ to 2½ feet bgs.
No caving observed.
No groundwater seepage observed.
Test Pit TP-10
Location: West portion of site, north of transmission lines
Approximate Elevation: 476’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 3 SM Tan silty SAND with gravel and small roots (medium dense, moist) (weathered till)
3 - 8 SM Gray silty SAND with gravel and occasional cobbles, moderately cemented (dense to very
dense, moist) (glacial till)
8 - 9 GP Brown poorly-graded GRAVEL with silt and sand (dense, moist) (advance outwash)
Terminated at 9 feet below ground surface.
No mottling observed.
No caving observed.
No groundwater seepage observed.
Logged by: NAF Excavated on: October 9, 2019
Test Pit Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-6
Test Pit TP-11
Location: Southwest portion of site
Approximate Elevation: 480’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 3 SM Tan silty SAND with gravel and roots, mottled at bottom contact (medium dense, moist)
(weathered till)
3 - 8½ SM Gray silty SAND with gravel, moderately cemented (dense to very dense, moist) (glacial till)
Terminated at 8¼ feet below ground surface.
Mottling observed from 2 to 3 feet bgs.
No caving observed.
No groundwater seepage observed.
Test Pit TP-12
Location: Vicinity of proposed body shop
Approximate Elevation: 486’
Depth (ft) Soil Type Soil Description
0 - 1¼ - Topsoil/rootzone
1¼ - 3½ SM Tan to mottled gray silty SAND with gravel (medium dense, moist) (weathered till)
3½ - 8½ SM Gray silty SAND with gravel, moderately cemented (dense to very dense, moist) (glacial
till)
Terminated at 8½ feet below ground surface.
Mottling observed from 2½ to 3½ feet bgs.
No caving observed.
No groundwater seepage observed.
Test Pit TP-13
Location: Eastern portion of site
Approximate Elevation: 484’
Depth (ft) Soil Type Soil Description
0 - 1 - Topsoil/rootzone
1 - 3½ SM Tan to mottled gray silty SAND with gravel (medium dense, moist) (weathered till)
3½ - 9 SM Gray silty SAND with gravel and occasional cobbles, moderately cemented (dense to very
dense, moist) (glacial till)
Terminated at 9 feet below ground surface.
Mottling observed from 2 to 3½ feet bgs.
No caving observed.
No groundwater seepage observed.
Logged by: NAF Excavated on: October 9, 2019
Test Pit Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-7
Test Pit TP-101
Location: Proposed detention pond
Approximate Elevation: 471’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 3½ SM Tan to gray silty SAND with gravel (medium dense, moist) (weathered outwash)
3½ - 12 GP-GM Grayish brown GRAVEL with silt and sand (dense, moist to wet) (advance outwash)
Terminated at 12 feet below ground surface.
No mottling observed.
No caving observed.
Groundwater seepage observed below 7½ feet bgs.
Test Pit TP-102
Location: Proposed detention pond
Approximate Elevation: 469’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 3 SM Tan to gray silty SAND with gravel and scattered construction debris (medium dense,
moist) (fill)
3 - 4 SM Gray silty SAND with gravel and occasional cobbles (dense, moist) (till fill)
4 - 9 GP-GM Grayish brown GRAVEL with silt and sand (dense, moist to wet) (advance outwash)
Terminated at 8½ feet below ground surface.
No mottling observed.
No caving observed.
Minor groundwater seepage observed at 8½ feet bgs.
Logged by: NAF Excavated on: January 24, 2020
Test Pit Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-8
Test Pit TP-103
Location: NW portion of site
Approximate Elevation: 446’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 2 SM Tan to brown silty SAND with small roots (medium dense, moist) (weathered outwash)
2 - 5 SP Brown SAND with trace gravel (medium dense, moist) (advance outwash)
5 - 9 GP Gray GRAVEL with sand (dense, moist) (advance outwash)
Terminated at 9 feet below ground surface.
No mottling observed.
No caving observed.
Groundwater seepage observed below 8 feet bgs.
Logged by: NAF Excavated on: January 24, 2020
Test Pit Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-9
Pilot Infiltration Test PIT-1
Location: Northwest portion of site
Approximate Elevation: 460’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil/rootzone
½ - 2 SM Tan silty SAND with some gravel and small roots (medium dense, moist) (weathered
outwash)
2 - 6 SP Brown poorly-graded SAND with gravel (dense, moist) (advance outwash)
Terminated at 6 feet below ground surface.
No mottling observed.
No caving observed.
No groundwater seepage observed.
Pilot Infiltration Test PIT-2
Location: Northwest of proposed shop
Approximate Elevation: 442’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil
½ - 2½ SM Tan to dark brown silty SAND with some gravel (medium dense, moist) (weathered
outwash)
2½ - 6½ GM Dark brown silty GRAVEL (medium dense to dense, moist) (advance outwash)
Terminated at 6½ feet below ground surface.
No mottling observed.
No caving observed.
No groundwater seepage observed.
Logged by: NAF Excavated on: January 24, 2020
PIT Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-10
Pilot Infiltration Test PIT-3
Location: Northern portion of site
Approximate Elevation: 452’
Depth (ft) Soil Type Soil Description
0 - ½ - Topsoil
½ - 2½ SM Tan to gray silty SAND and relict topsoil (loose to medium dense, moist) (fill / reworked
soil)
2½ - 4½ SM Tan silty SAND with gravel (medium dense, moist) (weathered till)
4½ - 7½ SM Gray silty SAND with gravel (dense, moist) (glacial till)
7½ - 10 GM Tan silty GRAVEL with sand (dense, moist) (advance outwash)
Terminated at 10 feet below ground surface.
No mottling observed.
No caving observed.
No groundwater seepage observed.
Logged by: NAF Excavated on: January 24, 2020
PIT Logs
Proposed Commercial Development
xxx South 320th Street
Federal Way, Washington
PN: 0921049-028, -139, -140, -160, -206, and -316
Doc ID: PapeKenworthNW.FederalWay.F February 2020 Figure A-11
0
5
10
15
20
25
30
450
445
440
435
430
425
420
Brown to gray silty sand with trace gravel
(loose, moist) (SM) (fill)
Grayish brown GRAVEL with silt and sand
(medium dense to very dense, moist) (GP-
GM) (advance outwash)
Bottom of Boring
Completed1/7/20
1
2
3
4
72
3
4
6
7
9
9
16
20
38
7
27
45
TOTAL DEPTH:21.5 EXCAVATION METHOD:LOGGED BY:NAF
TOP ELEVATION:450 EXCAVATION COMPANY:Boretec HAMMER TYPE:Cat-head
LATITUDE:EQUIPMENT:TD-85 HAMMER WEIGHT:140 lb
LONGITUDE:NOTES:
NOTES Proposed Commercial Development
1. Refer to log key for definition of symbols, abbreviations and codes
2. USCS designation is based on visual manual classification Federal Way, WA
and selected lab testing
3. Groundwater level, if indicated, is for the date shown and may vary
4. N.E. = Not Encountered LOG OF BORING B-1
JOB: PapeKenworthNW.320th Sheet 1 of
GeoResources, LLC FIG.DepthElevationSOIL DESCRIPTION Drilling
Notes
SampleSamplerSymbolTest Results
(new title)
TEST RESULTS
10 20 30 40 50
Penetration - (blow per foot)
% Fines (<0.075mm)
% Water Content
Plastic Limit Liquid Limit Blow
Count GroundWater1
0
5
10
15
20
25
30
450
445
440
435
430
425
Brown to gray silty SAND with gravel
(medium dense, moist) (SM) (weathered
advance)
Grayish brown silty GRAVEL with sand
(dense, moist) (GM) (advance outwash)
Grayish brown well-graded GRAVEL with silt
and sand (dense to very dense, moist) (GW-
GM) (advance outwash)
Bottom of Boring
Completed1/7/20
1
2
3
4
100
73
15
23
25
25
23
20
50/3"
15
27
44
TOTAL DEPTH:20.5 EXCAVATION METHOD:LOGGED BY:NAF
TOP ELEVATION:452 EXCAVATION COMPANY:Boretec HAMMER TYPE:Cat-head
LATITUDE:EQUIPMENT:TD-85 HAMMER WEIGHT:140 lb
LONGITUDE:NOTES:
NOTES Proposed Commercial Development
1. Refer to log key for definition of symbols, abbreviations and codes
2. USCS designation is based on visual manual classification Federal Way, WA
and selected lab testing
3. Groundwater level, if indicated, is for the date shown and may vary
4. N.E. = Not Encountered LOG OF BORING B-2
JOB: PapeKenworthNW.320th Sheet 1 of
GeoResources, LLC FIG.DepthElevationSOIL DESCRIPTION Drilling
Notes
SampleSamplerSymbolTest Results
(new title)
TEST RESULTS
10 20 30 40 50
Penetration - (blow per foot)
% Fines (<0.075mm)
% Water Content
Plastic Limit Liquid Limit Blow
Count GroundWater1
0
5
10
15
20
25
30
450
445
440
435
430
425
420
Brown to gray silty sand with trace gravel
(loose, moist) (SM) (fill)
Brown to gray silty SAND with gravel
(medium dense, moist) (SM) (weathered
advance)
Grayish brown GRAVEL with silt and sand
(dense to very dense, moist to wet) (GP-
GM) (advance outwash)
Bottom of Boring
Completed1/7/20
1
2
3
4
100
100
2
2
1
14
20
18
22
50/6"
18
50/4"
TOTAL DEPTH:21.5 EXCAVATION METHOD:LOGGED BY:NAF
TOP ELEVATION:451 EXCAVATION COMPANY:Boretec HAMMER TYPE:Cat-head
LATITUDE:EQUIPMENT:TD-85 HAMMER WEIGHT:140 lb
LONGITUDE:NOTES:
NOTES Proposed Commercial Development
1. Refer to log key for definition of symbols, abbreviations and codes
2. USCS designation is based on visual manual classification Federal Way, WA
and selected lab testing
3. Groundwater level, if indicated, is for the date shown and may vary
4. N.E. = Not Encountered LOG OF BORING B-3
JOB: PapeKenworthNW.320th Sheet 1 of
GeoResources, LLC FIG.DepthElevationSOIL DESCRIPTION Drilling
Notes
SampleSamplerSymbolTest Results
(new title)
TEST RESULTS
10 20 30 40 50
Penetration - (blow per foot)
% Fines (<0.075mm)
% Water Content
Plastic Limit Liquid Limit Blow
Count GroundWater1
0
5
10
15
20
25
30
480
475
470
465
460
455
Tan silty SAND with gravel (medium dense,
moist) (SM) (weathered till)
Gray silty SAND with gravel (very dense,
moist) (SM) (glacial till)
Bottom of Boring
Completed1/7/20
1
2
3
82+
100
100
10
32
50/5"
50/4"
50/5"
TOTAL DEPTH:15.5 EXCAVATION METHOD:LOGGED BY:NAF
TOP ELEVATION:484 EXCAVATION COMPANY:Boretec HAMMER TYPE:Cat-head
LATITUDE:EQUIPMENT:TD-85 HAMMER WEIGHT:140 lb
LONGITUDE:NOTES:
NOTES Proposed Commercial Development
1. Refer to log key for definition of symbols, abbreviations and codes
2. USCS designation is based on visual manual classification Federal Way, WA
and selected lab testing
3. Groundwater level, if indicated, is for the date shown and may vary
4. N.E. = Not Encountered LOG OF BORING B-4
JOB: PapeKenworthNW.320th Sheet 1 of
GeoResources, LLC FIG.DepthElevationSOIL DESCRIPTION Drilling
Notes
SampleSamplerSymbolTest Results
(new title)
TEST RESULTS
10 20 30 40 50
Penetration - (blow per foot)
% Fines (<0.075mm)
% Water Content
Plastic Limit Liquid Limit Blow
Count GroundWater1
0
5
10
15
20
25
30
470
465
460
455
450
445
Well-graded GRAVEL (dense, moist) (GW)
(surficial crushed rock)
Gray silty SAND with gravel (very dense,
moist) (SM) (glacial till)
Bottom of Boring
Completed1/7/20
1
2
100
100
100
40
50/4"
50/2"
50/2"
TOTAL DEPTH:15.5 EXCAVATION METHOD:LOGGED BY:NAF
TOP ELEVATION:474 EXCAVATION COMPANY:Boretec HAMMER TYPE:Cat-head
LATITUDE:EQUIPMENT:TD-85 HAMMER WEIGHT:140 lb
LONGITUDE:NOTES:
NOTES Proposed Commercial Development
1. Refer to log key for definition of symbols, abbreviations and codes
2. USCS designation is based on visual manual classification Federal Way, WA
and selected lab testing
3. Groundwater level, if indicated, is for the date shown and may vary
4. N.E. = Not Encountered LOG OF BORING B-5
JOB: PapeKenworthNW.320th Sheet 1 of
GeoResources, LLC FIG.DepthElevationSOIL DESCRIPTION Drilling
Notes
SampleSamplerSymbolTest Results
(new title)
TEST RESULTS
10 20 30 40 50
Penetration - (blow per foot)
% Fines (<0.075mm)
% Water Content
Plastic Limit Liquid Limit Blow
Count 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 34.7 14.1 2.4 26.9 18.6 3.36 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 422 & 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:Location: TP-2, S-1, D:6-8'
Sample Number: 098502
Client:
Project:
Project No:Figure
poorly graded gravel with sand
3.0
2.5
2.0
1.5
1.25
1
.75
.5
.3125
#4
#10
#20
#40
#60
#100
#200
100.0
100.0
100.0
88.4
88.4
75.4
65.3
58.2
55.3
51.2
48.8
43.0
21.9
7.1
4.3
3.3
NP NV NP
GP A-1-a
39.6492 29.9556 14.0964
3.0690 0.5544 0.3315
0.2772 50.86 0.08
Moisture: 4.7-percent
10/9/19 10/15/19
NF
KSS
PM
10/9/19
Pape Group
Proposed Commercial Development
Pape.S320th
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
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 13.5 11.1 4.5 13.4 24.9 32.66 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 422 & 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:Location: TP-5, S-1, D: 5-7'
Sample Number: 098506
Client:
Project:
Project No:Figure
silty sand with gravel
3.0
2.5
2.0
1.5
1.25
1
.75
.5
.3125
#4
#10
#20
#40
#60
#100
#200
100.0
100.0
100.0
100.0
100.0
97.4
86.5
84.3
81.3
75.4
70.9
65.9
57.5
48.8
40.5
32.6
NP NV NP
SM A-2-4(0)
20.8988 14.4894 0.5219
0.2683
Moisture: 8.7-percent
10/9/19 10/15/19
NF
KSS
PM
10/9/19
Pape Group
Proposed Commercial Development
Pape.S320th
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-2
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 22.7 27.0 9.1 18.4 12.3 10.56 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 422 & 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:Location: TP-8, S-2, D: 7-9'
Sample Number: 098509
Client:
Project:
Project No:Figure
poorly graded gravel with silt and sand
3.0
2.5
2.0
1.5
1.25
1
.75
.5
.3125
#4
#10
#20
#40
#60
#100
#200
100.0
100.0
100.0
100.0
100.0
91.1
77.3
67.8
62.4
50.3
41.2
32.8
22.8
15.6
12.3
10.5
NP NV NP
GP-GM A-1-a
24.8048 22.3624 7.1814
4.6305 0.6982 0.2285
Moisture: 4.6-percent
10/9/19 10/15/19
NF
KSS
PM
10/9/19
Pape Group
Proposed Commercial Development
Pape.S320th
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-3
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 7.1 9.6 3.9 10.2 21.5 47.76 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 422 & 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:Location: TP-13, S-3, D: 2-3.5'
Sample Number: 098514
Client:
Project:
Project No:Figure
silty sand with gravel
3.0
2.5
2.0
1.5
1.25
1
.75
.5
.3125
#4
#10
#20
#40
#60
#100
#200
100.0
100.0
100.0
100.0
100.0
96.4
92.9
88.3
86.8
83.3
79.4
75.5
69.2
61.0
53.7
47.7
NP NV NP
SM A-4(0)
14.7889 6.1111 0.2327
0.0980
Moisture: 9.7-percent
10/9/19 10/15/19
NF
KSS
PM
10/9/19
Pape Group
Proposed Commercial Development
Pape.S320th
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-4
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 27.4 16.4 6.8 16.9 17.5 15.06 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 422 & 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: B-2 Depth: 5
Sample Number: 1
Client:
Project:
Project No:Figure
silty gravel with sand
3.0
2.5
2.0
1.5
1.25
1
.75
.5
.3125
#4
#10
#20
#40
#60
#100
#200
100.0
100.0
100.0
100.0
100.0
85.4
72.6
70.0
66.0
56.2
49.4
42.1
32.5
25.3
20.0
15.0
NP NV NP
GM A-1-b
27.2488 25.1699 5.7966
2.1668 0.3527
Moisture: 8.5%
1/7/20 1/9/20
NAF
KSS
PM
1/7/20
Pape Kenworth NW
Proposed Commercial Development
PapeKenworthNW.320th
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-5
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 12.8 36.7 12.2 19.7 9.9 8.76 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 422 & 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: B-2 Depth: 20
Sample Number: 4
Client:
Project:
Project No:Figure
well-graded gravel with silt and sand
3.0
2.5
2.0
1.5
1.25
1
.75
.5
.3125
#4
#10
#20
#40
#60
#100
#200
100.0
100.0
100.0
100.0
100.0
100.0
87.2
73.2
65.0
50.5
38.3
27.2
18.6
14.1
11.4
8.7
NP NV NP
GW-GM A-1-a
20.2726 17.8574 6.6410
4.5801 1.0545 0.2784
0.1047 63.44 1.60
Moisture: 7.0%
1/7/20 1/9/20
NAF
KSS
PM
1/7/20
Pape Kenworth NW
Proposed Commercial Development
PapeKenworthNW.320th
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-6
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 19.3 26.9 12.1 23.5 16.4 1.86 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:Location: PIT-1, S-1
Sample Number: PIT1 S1
Client:
Project:
Project No:Figure
poorly graded SAND with gravel
3.0
2.5
2.0
1.5
1.25
1.0
.75
.5
0.375
#4
#10
#20
#40
#60
#100
#200
100.0
100.0
100.0
89.6
89.6
89.6
80.7
74.9
68.3
53.8
41.7
31.6
18.2
6.6
2.8
1.8
NP NV NP
SP A-1-a
38.5116 21.8721 6.3959
3.6190 0.7839 0.3667
0.2920 21.90 0.33
Moisture: 5.1%
1/29/2020
MM
KSS
PM
1/24/2020
Pape Kenworth NW
Proposed Commercial Development
PapeKenworthNW.320th
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-7
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 21.6 28.0 9.1 11.8 9.6 19.96 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:Location: PIT-2, S-1
Sample Number: PIT2 S1
Client:
Project:
Project No:Figure
silty GRAVEL with sand
3.0
2.5
2.0
1.5
1.25
1
.75
.5
0.375
#4
#10
#20
#40
#60
#100
#200
100.0
100.0
100.0
91.7
91.7
85.3
78.4
70.3
62.2
50.4
41.3
35.4
29.5
24.8
22.0
19.9
NP NV NP
GM A-1-b
29.9367 25.0571 8.3680
4.5826 0.4523
Moistue: 7.5%
1/24/2020 1/29/2020
MM
KSS
PM
1/24/2020
Pape Kenworth NW
Proposed Commercial Development
PapeKenworthNW.320th
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-8
BEARING RATIO TEST REPORT
ASTM 01883-16
500 CBR at 95% Max. Density = 5.0%
for 0.10 in. Penetration
11
9 ~5~1--
400 V-17 -~ / 0 -g: 7 V m 125 blows I -0
'iii / L Q. 5 -V ! III 300 u V .1~~"----C I 1\1 -3 I III 'iii / 112 116 120 124 128 132
III Molded Density (pet) g:
c V 0 .. 2 e -200 V III I~ c
III / 1.6 /-D.
L--------1.2 ~ 0 / L--------
100 / ...-' -; ~ / .----'" 0.8 ~ ~ -------
0.4 ~ ~
0 0
0 0.1 0 .2 0.3 0.4 0.5 0 24 48 72 96
Penetration Depth (in.) Elapsed Time (hrs)
Molded Soaked eBR "I.;) Linearity Surcharge Max.
Density Percent of Moisture Density I Percent of 1 Moisture 0.10 in. 0.20 In. Correction (Ibs.) Swell
(pet) Max. Dens. (%) (pet) Max. Dens. (%) (in.) (%)
1 • 117.4 90.9 9.6 ~ 90.1
I
15.5 3.7 4.8 -0.054 10 0.9
-I
2 • 124.3 96.2 9 .7 123 .0 *8 5.6 7.4 -0.048 10 1
-----
3 • 129.1 99.9 9.8 127.1 98.4 11.4 8.4 11.2 -0.036 10 1.5
Material Description Max. Optimum uses ~:~. Moisture LL PI
(%)
Brown silty sand with gravel. -129.2 9.7 --
Project No: 066-19359 Test Description/Remarks:
Project: Pape -S. 320th #098514 ASTMD1557
Source of Sample: Client Supplied Sample
Sample Number: 19L556 Sample ID: 19L556
Sample Date: 1 0-9-19
Date: 10-9-19
6i1Krazan Figure
Appendix C
Global Stability Analyses
2.22.2
W
W
2.22.2
Material Name Color Unit Weight
(lbs/Ō3)Strength Type Cohesion
(psf)
Phi
(deg)Water Surface Hu Type Ru
Weathered Soil 125 Mohr-Coulomb 100 34 Water Surface AutomaƟcally Calculated
Glacial Till 138 Mohr-Coulomb 500 38 None 0
Advance Outwash 135 Mohr-Coulomb 100 42 Water Surface AutomaƟcally Calculated600500400300
-100 -50 0 50 100 150 200 250 300 350 400 450
Analysis Description Global Stability Analysis
Company GeoResources, LLCScale1:700Drawn By NAF
File Name Pape.320th.PondStability.rev1.slmdDate20191104
Project
Pape.S320thSt
SLIDEINTERPRET 8.029
1.21.2
W
W
1.21.2
Material Name Color Unit Weight
(lbs/Ō3)Strength Type Cohesion
(psf)
Phi
(deg)Water Surface Hu Type Ru
Weathered Soil 125 Mohr-Coulomb 100 34 Water Surface AutomaƟcally Calculated
Glacial Till 138 Mohr-Coulomb 500 38 None 0
Advance Outwash 135 Mohr-Coulomb 100 42 Water Surface AutomaƟcally Calculated
0.26
Safety Factor
0.0
0.3
0.5
0.8
1.0
1.3
1.5
1.8
2.0
2.3
2.5
2.8
3.0
3.3
3.5
3.8
4.0
4.3
4.5
4.8
5.0
5.3
5.5
5.8
6.0+600550500450400350300-100 -50 0 50 100 150 200 250 300 350 400 450
Analysis Description Global Stability Analysis
Company GeoResources, LLCScale1:700Drawn By NAF
File Name Pape.320th.PondStability.rev1.slmdDate20191104
Project
Pape.S320thSt
SLIDEINTERPRET 8.029
2.02.0
W
W
2.02.0
Material Name Color Unit Weight
(lbs/Ō3)Strength Type Cohesion
(psf)
Phi
(deg)Water Surface Hu Type Hu Ru
Weathered Soil 125 Mohr-Coulomb 100 34 Water Surface AutomaƟcally Calculated
Glacial Till 138 Mohr-Coulomb 500 38 None 0
Advance Outwash 135 Mohr-Coulomb 100 42 Water Surface AutomaƟcally Calculated
Till Fill / Liner 135 Mohr-Coulomb 100 35 Water Surface Custom 1
Saturated Advance Outwash 135 Mohr-Coulomb 100 42 None 0
Water 62.4 No strength None 0600550500450400350
300-100 -50 0 50 100 150 200 250 300 350 400 450
Analysis Description Global Stability Analysis
Company GeoResources, LLCScale1:700Drawn By NAF
File Name Pape.320th.PondStability.rev1.slmdDate20191104
Project
Pape.S320thSt
SLIDEINTERPRET 8.029
1.11.1
W
W
1.11.1 0.26
Material Name Color Unit Weight
(lbs/Ō3)Strength Type Cohesion
(psf)
Phi
(deg)Water Surface Hu Type Hu Ru
Weathered Soil 125 Mohr-Coulomb 100 34 Water Surface AutomaƟcally Calculated
Glacial Till 138 Mohr-Coulomb 500 38 None 0
Advance Outwash 135 Mohr-Coulomb 100 42 None 0
Till Fill / Liner 135 Mohr-Coulomb 100 35 None 0
Saturated Advance Outwash 135 Mohr-Coulomb 100 42 Water Surface AutomaƟcally Calculated
Safety Factor
0.0
0.3
0.5
0.8
1.0
1.3
1.5
1.8
2.0
2.3
2.5
2.8
3.0
3.3
3.5
3.8
4.0
4.3
4.5
4.8
5.0
5.3
5.5
5.8
6.0+700600500400-100 -50 0 50 100 150 200 250 300 350 400 450
Analysis Description Global Stability Analysis
Company GeoResources, LLCScale1:700Drawn By NAF
File Name Pape.320th.PondStability.rev1.slmdDate20191104
Project
Pape.S320thSt
SLIDEINTERPRET 8.029
2.02.0
W
W
2.02.0
Material Name Color Unit Weight
(lbs/Ō3)Strength Type Cohesion
(psf)
Phi
(deg)Water Surface Hu Type Ru
Weathered Soil 125 Mohr-Coulomb 100 34 Water Surface AutomaƟcally Calculated
Glacial Till 138 Mohr-Coulomb 500 38 None 0
Advance Outwash 135 Mohr-Coulomb 100 42 None 0
Till Fill / Liner 135 Mohr-Coulomb 100 35 None 0
Saturated Advance Outwash 135 Mohr-Coulomb 100 42 Water Surface AutomaƟcally Calculated650
600550500450400350-100 -50 0 50 100 150 200 250 300 350 400 450
Analysis Description Global Stability Analysis
Company GeoResources, LLCScale1:700Drawn By NAF
File Name Pape.320th.PondStability.rev1.slmdDate20191104
Project
Pape.S320thSt
SLIDEINTERPRET 8.029
1.51.5
W
W
1.51.5
Material Name Color Unit Weight
(lbs/Ō3)Strength Type Cohesion
(psf)
Phi
(deg)Water Surface Hu Type Ru
Weathered Soil 125 Mohr-Coulomb 100 34 Water Surface AutomaƟcally Calculated
Glacial Till 138 Mohr-Coulomb 500 38 None 0
Advance Outwash 135 Mohr-Coulomb 100 42 Water Surface AutomaƟcally Calculated
Muck 80 Mohr-Coulomb 100 26 Water Surface AutomaƟcally Calculated
Undocumented Fill 115 Mohr-Coulomb 0 30 Water Surface AutomaƟcally Calculated
0.26700
600500400-50 0 50 100 150 200 250 300 350 400 450 500
Analysis Description Global Stability Analysis
Company GeoResources, LLCScale1:700Drawn By NAF
File Name Pape.320th.WallStability.rev1.slmdDate20191104
Project
Pape.S320thSt
SLIDEINTERPRET 8.029
3.33.3
W
W
3.33.3
Material Name Color Unit Weight
(lbs/Ō3)Strength Type Cohesion
(psf)
Phi
(deg)Water Surface Hu Type Ru
Weathered Soil 125 Mohr-Coulomb 100 34 Water Surface AutomaƟcally Calculated
Glacial Till 138 Mohr-Coulomb 500 38 None 0
Advance Outwash 135 Mohr-Coulomb 100 42 Water Surface AutomaƟcally Calculated
Muck 80 Mohr-Coulomb 100 26 Water Surface AutomaƟcally Calculated
Undocumented Fill 115 Mohr-Coulomb 0 30 None 0550500450400350300
250-50 0 50 100 150 200 250 300 350 400 450 500
Analysis Description Global Stability Analysis
Company GeoResources, LLCScale1:700Drawn By NAF
File Name Pape.320th.WallStability.rev1.slmdDate20191104
Project
Pape.S320thSt
SLIDEINTERPRET 8.029
1.81.8
W
W
1.81.8
RuHu TypeWater
Surface
Allow
Sliding
Phi
(deg)
Cohesion
(psf)Strength TypeUnit Weight (lbs/
ft3)ColorMaterial Name
Automatically
CalculatedWater Surface34100Mohr-Coulomb125Weathered Soil
0None38500Mohr-Coulomb138Glacial Till
Automatically
CalculatedWater Surface42100Mohr-Coulomb135Advance
Outwash
Automatically
CalculatedWater Surface350Mohr-Coulomb130Structural Fill
0NoneYesInfinite
strength130MSE Wall
Automatically
CalculatedWater Surface400Mohr-Coulomb135Gravel Backfill
Automatically
CalculatedWater Surface26100Mohr-Coulomb80Muck700600
500400-50 0 50 100 150 200 250 300 350 400 450 500
Scenario Proposed Retaining Walls - StaticGroupGroup 3
Company GeoResources, LLCDrawn By NAF
File Name Pape.320th.WallStability.rev1.slmdDate20191104
Project
Pape.S320thSt
SLIDEINTERPRET 9.005
1.21.2
W
W
1.21.2 RuHu TypeWater
Surface
Allow
Sliding
Phi
(deg)
Cohesion
(psf)Strength TypeUnit Weight (lbs/
ft3)ColorMaterial Name
Automatically
Calculated
Water
Surface34100Mohr-
Coulomb125Weathered Soil
0None38500Mohr-
Coulomb138Glacial Till
Automatically
Calculated
Water
Surface42100Mohr-
Coulomb135Advance
Outwash
Automatically
Calculated
Water
Surface350Mohr-
Coulomb130Structural Fill
0NoneYesInfinite
strength130MSE Wall
Automatically
Calculated
Water
Surface400Mohr-
Coulomb135Gravel Backfill
Automatically
Calculated
Water
Surface26100Mohr-
Coulomb80Muck
0.26700
600500400-50 0 50 100 150 200 250 300 350 400 450 500
Scenario Proposed Retaining Walls - SeismicGroupGroup 3
Company GeoResources, LLCDrawn By NAF
File Name Pape.320th.WallStability.rev1.slmdDate20191104
Project
Pape.S320thSt
SLIDEINTERPRET 9.005