HomeMy WebLinkAboutEx_10_Geotech_ReportGeotechnical Engineering Report
Brotherton Cadillac Auto Dealership
215 SW 12th St
Renton, WA 98037
Parcel Nos. 3340402850, 3340402860, 3340402870,
3340402820, 3340402885, 3340402805,
3340402880, 3340402780, and 3340402925
July 8, 2021
prepared for:
Brotherton Buick GMC
215 SW 12th St #201
Renton, Washington 98057
prepared by:
Migizi Group, Inc.
PO Box 44840
Tacoma, Washington 98448
(253) 537-9400
MGI Project P2411-T21
Exhibit 10
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
i
TABLE OF CONTENTS
Page No.
1.0 SITE AND PROJECT DESCRIPTION .............................................................................................. 1
2.0 EXPLORATORY METHODS ............................................................................................................ 2
2.1 Auger Boring Procedures...................................................................................................... 3
3.0 SITE CONDITIONS ............................................................................................................................ 3
3.1 Surface Conditions ................................................................................................................. 3
3.2 Soil Conditions ....................................................................................................................... 4
3.3 Groundwater Conditions ...................................................................................................... 5
3.4 Infiltration Conditions ........................................................................................................... 5
3.5 Seismic Conditions ................................................................................................................. 5
3.6 Liquefaction Potential ........................................................................................................... 6
4.0 CONCLUSIONS AND RECOMMENDATIONS............................................................................ 7
4.1 Site Preparation ...................................................................................................................... 8
4.2 Spread Footings .................................................................................................................... 10
4.3 Slab-On-Grade-Floors .......................................................................................................... 11
4.4 Subgrade and Retaining Walls ........................................................................................... 12
4.5 Asphalt Pavement ................................................................................................................. 13
4.6 Structural Fill ........................................................................................................................ 14
5.0 RECOMMENDED ADDITIONAL SERVICES ............................................................................. 15
6.0 CLOSURE ........................................................................................................................................... 16
List of Tables
Table 1. Approximate Locations and Depths of Explorations ............................................................................. 2
Table 2. Laboratory Test Results for Non-Organic Onsite Soils .......................................................................... 6
List of Figures
Figure 1. Topographic and Location Map
Figure 2. Site and Exploration Plan
APPENDIX A
Soil Classification Chart and Key to Test Data .................................................................................................. A-1
Logs of Auger Borings B-1 through B-3 .................................................................................................... A-2…A-4
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Page 1 of 16
MIGIZI GROUP, INC.
PO Box 44840 PHONE (253) 537-9400
Tacoma, Washington 98448 FAX (253) 537-9401
July 8, 2021
Brotherton Buick GMC
215 SW 12th St #201
Renton, WA 98057
c/o Castino Architecture
8911 71st Ave NW
Gig Harbor, WA 98332
Attention: James H. Castino, Principal
Subject: Geotechnical Engineering Report
Brotherton Cadillac Auto Dealership
215 SW 12th St
Renton, WA 98037
Parcel Nos. 3340402850, 3340402860, 3340402870, 3340402820, 3340402885,
3340402805, 3340402880, 3340402780, and 3340402925
MGI Project P2411-T21
Dear Mr. Castino:
Migizi Group, Inc. (MGI) is pleased to submit this report describing the results of our geotechnical
engineering evaluation of the improvements proposed for the existing Brotherton Buick GMC
facility and the construction of the new Brotherton Cadillac complex in Renton, Washington.
This report has been prepared for the exclusive use of Brotherton Buick GMC, Castino
Architecture, and their consultants, for specific application to this project, in accordance with
generally accepted geotechnical engineering practice.
1.0 SITE AND PROJECT DESCRIPTION
The project site consists of nine contiguous tax parcels immediately northwest of the intersection
between State Route 167 and State Route 405, towards the west-central portion of the city limits of
Renton, Washington, as shown on the enclosed Topographic and Location Map (Figure 1). Five of
the aforementioned tax parcels (3340402850, 3340402860, 3340402870, 3340402820, 3340402885) are
associated with the existing Brotherton GMC facility, whereas the remaining four parcels
(3340402805, 3340402880, 3340402780, 3340402925) occupy the space proposed for the new
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 2 of 16
Cadillac showroom and sales building. The work area is irregularly shaped, encompassing a total
area of approximately 2.83-acres. The existing Brotherton GMC facility consists of a 27,897-sf
masonry showroom and sales building. Areas immediately around the structure contain asphalt
pavements for vehicle storage and drive lanes. The proposed Cadillac site is currently occupied
by single-family residences and private gravel parking areas.
Improvement plans involve the construction of a new 4,560-sf service bay expansion towards the
southwest corner of the existing GMC masonry building, the clearing/stripping/grading of
properties immediately east of the Brotherton GMC facility, and the construction of a new
Brotherton Cadillac complex, which will largely be occupied by a new 14,330-sf Cadillac
showroom/sales building and asphalt pavements. Site produced stormwater will be retained
onsite if feasible.
2.0 EXPLORATORY METHODS
We explored surface and subsurface conditions at the project site on April 26, 2021. Our
exploration and evaluation program comprised the following elements:
• Surface reconnaissance of the site,
• Three auger boring explorations (designated B-1 through B-3), advanced on April 26, 2021,
and
• A review of published geologic and seismologic maps and literature.
Table 1 summarizes the approximate functional locations and termination depths of our
subsurface explorations, and Figure 2 depicts their approximate relative locations. The following
sections describe the procedures used for excavation of borings.
TABLE 1
APPROXIMATE LOCATIONS AND DEPTHS OF EXPLORATIONS
Exploration Functional Location
Termination
Depth
(feet)
B-1
B-2
B-3
Northeast corner of proposed service bay expansion area
Southwest corner of proposed service bay expansion area
Side yard space between 209 & 201 SW 12th St
36½
36½
36½
The specific number and locations of our explorations were selected in relation to the existing site
features, under the constraints of surface access, underground utility conflicts, and budget
considerations.
It should be realized that the explorations performed and utilized for this evaluation reveal
subsurface conditions only at discrete locations across the project site and that actual conditions in
other areas could vary. Furthermore, the nature and extent of any such variations would not
become evident until additional explorations are performed or until construction activities have
begun. If significant variations are observed at that time, we may need to modify our conclusions
and recommendations contained in this report to reflect the actual site conditions.
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Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 3 of 16
2.1 Auger Boring Procedures
Our exploratory borings were advanced through the soil with a hollow stem auger, using a truck
mounted drill rig operated by an independent drilling firm working under subcontract to MGI.
An engineering geologist from our firm continuously observed the borings, logged the subsurface
conditions, and collected representative soil samples. All samples were stored in watertight
containers and later transported to a laboratory for further visual examination. After the borings
were completed, they were backfilled with bentonite chips.
Throughout the drilling operation, soil samples were obtained at 2½ or 5-foot depth intervals by
means of the Standard Penetration Test (SPT) per ASTM:D-1586. This testing and sampling
procedure consists of driving a standard 2-inch-diameter steel split-spoon sampler 18 inches into
the soil with a 140-pound hammer free-falling 30 inches. The number of blows required to drive
the sampler through each 6-inch interval is counted, and the total number of blows struck during
the final 12 inches is recorded as the Standard Penetration Resistance, or "SPT blow count." If a
total of 50 blows are struck within any 6-inch interval, the driving is stopped and the blow count
is recorded as 50 blows for the actual penetration distance. The resulting Standard Penetration
Resistance values indicate the relative density of granular soils and the relative consistency of
cohesive soils.
The enclosed boring logs (Appendix A) describe the vertical sequence of soils and materials
encountered in the borings, based primarily on our field classifications and supported by our
subsequent laboratory examination and testing. Where a soil contact was observed to be
gradational, our logs indicate the average contact depth. Where a soil type changed between
sample intervals, we inferred the contact depth. Our logs also graphically indicate the blow
count, sample type, sample number, and approximate depth of each soil sample obtained from
the boring, as well as any laboratory tests performed on these soil samples. If any groundwater
was encountered in the borehole, the approximate groundwater depth is depicted on the boring
log. Groundwater depth estimates are typically based on the moisture content of soil samples, the
wetted height on the drilling rods, and the water level measured in the borehole after the auger
has been extracted. The soils were classified visually in general accordance with the system
described in Figure A-1, which includes a key to the exploration logs. Summary logs of our
explorations are included as Figures A-2 through A-4.
3.0 SITE CONDITIONS
The following sections present our observations, measurements, findings, and interpretations
regarding surface, soil, groundwater, infiltration and seismic conditions, and liquefaction
potential.
3.1 Surface Conditions
As previously indicated, the project site consists of nine contiguous tax parcels immediately
northwest of the intersection between State Route 167 and State Route 405, towards the west-
central portion of the city limits of Renton, Washington. Five of the aforementioned tax parcels
(3340402850, 3340402860, 3340402870, 3340402820, 3340402885) are associated with the existing
Brotherton GMC facility, whereas the remaining four parcels (3340402805, 3340402880,
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 4 of 16
3340402780, 3340402925) occupy the space proposed for the new Cadillac showroom and sales
building. The work area is irregularly shaped, encompassing a total area of approximately
2.83-acres. The existing Brotherton GMC facility consists of a 27,897-sf masonry showroom and
sales building. Areas immediately around the structure contain asphalt pavements for vehicle
storage and drive lanes. The proposed Cadillac site is currently occupied by single-family
residences and private gravel parking areas.
Topographically, the project area is relatively level, with minimal grade change being observed,
with the site being located within the Duwamish River Valley, in close proximity to the historic
course of the Black River. In the vicinity of the existing Brotherton GMC facility, vegetation is
largely limited to lawn grasses along the western margin of the project area. Additionally, east of
this area, along the proposed Cadillac complex footprint, vegetation is more robust, being
incorporated into the landscaping of the four residential sites impacted by the proposed
improvements. In addition to lawn grasses, scattered growths of fir and cedar trees, and
ornamental shrubs and brush were also present.
No hydrologic features were observed on site, such as seeps, springs, ponds, and streams, nor
were there indications of surface hydrology, such ripple marks or scouring present.
3.2 Soil Conditions
Subsurface conditions were observed through the advancement of three auger boring
explorations, two in the vicinity of the proposed service bay expansion area and one adjacent to
the proposed Brotherton Cadillac site. In general, the explorations revealed relatively consistent
subgrade conditions, generally consisting of a surface mantle of sod and topsoil or asphaltic
concrete, underlain by native, alluvial deposits. The alluvial deposits encountered onsite are
generally associated with the historic channel of the Black River, which drained
Lake Washington until 1916, when the opening of the Lake Washington Ship Canal lowered the
lake, causing this part of the Black River to dry up.
The uppermost 8 feet of soil deposits encountered in our explorations are largely poorly
consolidated and fine-grained, ranging in composition from silty sand to silt. Underlying this
material are intermediate gravels, which were encountered in a medium dense to very dense in
situ condition and extended through a depth of 15 to 20 feet below existing grade, before
transitioning to another fine-grained soil horizon. In the vicinity auger boring exploration B-2, the
fine-grained horizon was 15 feet thick, whereas in the remaining two explorations, it was only
observed from a depth of 20 to 25 feet below the intermediate gravel. The final soil horizon
consists of deep gravels, which were again encountered in a medium dense to very dense in situ
condition. This deep gravel soil horizon was observed through the termination of all our
subsurface explorations, a maximum depth of 36½ feet below existing grade.
In the Geologic Map of the Tacoma 1:100,000-scale Quadrangle, Washington, as prepared by the
Washington State Department of Natural Resources Division of Geology and Earth Resources
(WSDNR) (2015), the entire project area is mapped as containing Qa, or Holocene alluvium, which
is described as loose, stratified to massively bedded fluvial silt, sand, and gravel; typically, well
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 5 of 16
rounded and moderately to well sorted; locally includes sandy to silty estuarine deposits. The
National Cooperative Soil Survey (NCSS) for King County classifies soils onsite as Urban Land,
indicating that surrounding areas have been significantly modified through manmade activities.
Our field observations generally correspond with the site classifications performed by the
WSDNR and the NCSS.
The enclosed exploration logs (Appendix A) provide a detailed description of the soil strata
encountered in our subsurface explorations.
3.3 Groundwater Conditions
We encountered groundwater in each of our subsurface explorations at a depth of approximately
8½ feet below existing grade. Given the fact that our explorations were conducted outside of
what is generally considered the rainy season in Western Washington (November 1 to March 31),
we anticipate that groundwater levels will rise higher than that which we observed. Seasonally
perched groundwater should be anticipated atop fine-grained soil lenses in close proximity to
existing grade. Groundwater levels will fluctuate with localized geology and levels of
precipitation.
3.4 Infiltration Conditions
As indicated in the Soil Conditions section of the report, the site is underlain by alluvial soils,
which can be readily subdivided into four soil horizons: upper fine-grained, intermediate gravel,
intermediate fine-grained, and deep gravels. Given the fact that groundwater levels rise higher
than 8½ feet below existing grade, the upper fine-grained soil horizon is the only horizon which
could potentially support infiltration. This material ranges in compositions from silty sand to silt,
the latter of which should be considered relatively impermeable. Given the hydrogeologic setting
of the project area, we do not interpret infiltration as being feasible for this project, and site
produced stormwater should be managed through detention, and/or diverted to an existing sewer
along SW 12th St.
3.5 Seismic Conditions
The site is in the Puget Sound basin which has experienced several earthquakes. A detailed
description of the regional seismicity is beyond the scope of this report; however, previous
regional earthquakes can be split into two general categories: 1.) large earthquakes with a moment
magnitude greater than 8.0 (MW > 8.0), and 2.) modest size earthquakes with a moment magnitude
generally less than 7.25 (MW < 7.25). In all cases, the thickness of the soil between the bedrock and
the ground surface can change (usually amplify) the seismically induced ground motions and
therefore the inertial loads acting on surface structures.
“Site Class” is a classification system used by the IBC and ASCE 7 to provide some insight to the
potential for ground motion amplification. The site class is based on the properties of the upper
100 feet of the soil and rock materials at the site. MGI used a combination of onsite explorations,
and our review of the geologic mapping of the site to derive a site class for the site. Based on
evaluation and the definitions of Site Class as provided in Table 20.3-1 of ASCE 7-16 (as required
by the 2018 International Building Code), the soil conditions on this site satisfy the definition of
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 6 of 16
Site Class D. Our evaluation assumes the soil conditions encountered in the bottom of our
explorations, and those from nearby properties, is similar to or increasing in density/consistency
down to 100 feet below ground surface.
The 2018 IBC considers earthquake shaking having a 2 percent probability of exceedance in
50 years (i.e. a 2475-year return period), as the code-based design requirement. Using the third-
party graphical user interface tools made available by the USGS at https://seismicmaps.org, MGI
derived the design ground motions to be used for design of the structures. Our evaluation used
IBC 2018 as the code reference, Risk Category I/II/III, and Site Class D. The results of our
evaluation are provided in Table 2 (below).
TABLE 2
SEISMIC DESIGN PARAMETERS
Parameter Value Basis
Site Class D Table 20.3-1 of ASCE 7-16
SS 1.441 seismicmaps.org
Fa 1.2A seismicmaps.org
SMS 1.73 = Fa · SS, 2018 IBC Eqn. 16-36
SDS 1.153 = 2/3 SMS, 2018 IBC Eqn. 16-38
S1 0.491 seismicmaps.org
FV 1.81B, C 2018 IBC
SM1 0.889B, C = FV · S1, 2018 IBC Eqn. 16-37
SD1 0.592B, C = 2/3 SM1, 2018 IBC Eqn. 16-39
PGA 0.613g seismicmaps.org
PGAM 0.736g seismicmaps.org
T0 -- C Not applicable
TS -- C Not applicable
TL 6 sec. seismicmaps.org
Notes:
A. Use the value provided unless the simplified design procedure of ASCE 7 Section 12.14 is
used. If this occurs, please contact our office for more information.
B. Based on Table 1613.2.3(2) of the 2018 IBC – An ASCE 7-16 Chapter 21 analysis has not been
performed.
C. More detailed seismic design criteria are available upon request. Please contact MGI’s office
for more information.
3.6 Liquefaction Potential
Liquefaction is a sudden increase in pore water pressure and a sudden loss of soil shear strength
caused by shear strains, as could result from an earthquake. Research has shown that saturated,
loose, fine to medium sands with a fines (silt and clay) content less than about 20 percent are most
susceptible to liquefaction. No significant lenses of poorly consolidated clean sands were
encountered through the termination of our explorations. We interpret site soils as posing a low
risk to liquefy during a large-scale seismic event.
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Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 7 of 16
4.0 CONCLUSIONS AND RECOMMENDATIONS
Improvement plans involve the construction of a new 4,560-sf service bay expansion towards the
southwest corner of the existing GMC masonry building, the clearing/stripping/grading of
properties immediately east of the Brotherton GMC facility, and the construction of a new
Brotherton Cadillac complex, which will largely be occupied by a new 14,330-sf Cadillac
showroom/sales building, and asphalt pavements. Site produced stormwater will be retained
onsite if feasible. We offer these recommendations:
• Feasibility: Based on our field explorations, research and analyses, the proposed
structures and pavements appear feasible from a geotechnical standpoint.
• Foundation Options: Over-excavation of spread footing subgrades, to a depth of 3 to
4 feet, and the construction of structural fill bearing pads, will be necessary for foundation
support of new structures. If foundation construction occurs during wet conditions, it is
likely that a geotextile fabric, placed between bearing pads and native soils, will also be
necessary. Recommendations for spread footings are provided in Section 4.2.
• Floor Options: We recommend over-excavation of slab-on-grade floor subgrades to a
minimum depth of 1½ feet, then placement of properly compacted structural fill as a floor
subbase. If floor construction occurs during wet conditions, it is likely that a geotextile
fabric, placed between the structural fill floor subbase and native soils, will be necessary.
Recommendations for slab-on-grade floors are included in Section 4.3. Fill underlying
floor slabs should be compacted to 95 percent (ASTM:D-1557).
• Pavement Sections: We recommend over-excavation of pavement subgrades to a
minimum depth of 12 inches, then placement of properly compacted structural fill as
pavement subbase. We recommend a conventional pavement section comprised of an
asphalt concrete pavement over a crushed rock base course over a properly prepared
(compacted) subgrade or a granular subbase, depending on subgrade conditions during
pavement subgrade preparation.
All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded
dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed
during this proof-rolling operation should be over-excavated to a depth of 2 feet and
replaced with a suitable structural fill material.
• Infiltration Conditions: As indicated in the Soil Conditions section of the report, the site is
underlain by alluvial soils, which can be readily subdivided into four soil horizons: upper
fine-grained, intermediate gravel, intermediate fine-grained, and deep gravels. Given the
fact that groundwater levels rise higher than 8½ feet below existing grade, the upper fine-
grained soil horizon is the only horizon which could potentially support infiltration. This
material ranges in compositions from silty sand to silt, the latter of which should be
considered relatively impermeable. Given the hydrogeologic setting of the project area,
we do not interpret infiltration as being feasible for this project, and site produced
stormwater should be managed through detention, or diverted to an existing along SW
12th St.
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 8 of 16
The following sections of this report present our specific geotechnical conclusions and
recommendations concerning site preparation, spread footings, slab-on-grade floors, subgrade
and retaining walls, asphalt pavement, and structural fill. The Washington State Department of
Transportation (WSDOT) Standard Specifications and Standard Plans cited herein refer to
WSDOT publications M41-10, Standard Specifications for Road, Bridge, and Municipal Construction,
and M21-01, Standard Plans for Road, Bridge, and Municipal Construction, respectively.
4.1 Site Preparation
Preparation of the project site should involve erosion control, temporary drainage, clearing,
stripping, excavations, cutting, subgrade compaction, and filling.
Erosion Control: Before new construction begins, an appropriate erosion control system should
be installed. This system should collect and filter all surface water runoff through silt fencing. We
anticipate a system of berms and drainage ditches around construction areas will provide an
adequate collection system. Silt fencing fabric should meet the requirements of WSDOT Standard
Specification 9-33.2 Table 6. In addition, silt fencing should embed a minimum of 6 inches below
existing grade. An erosion control system requires occasional observation and maintenance.
Specifically, holes in the filter and areas where the filter has shifted above ground surface should
be replaced or repaired as soon as they are identified.
Temporary Drainage: We recommend intercepting and diverting any potential sources of surface
or near-surface water within the construction zones before stripping begins. Because the selection
of an appropriate drainage system will depend on the water quantity, season, weather conditions,
construction sequence, and contractor's methods, final decisions regarding drainage systems are
best made in the field at the time of construction. Based on our current understanding of the
construction plans, surface, and subsurface conditions, we anticipate that curbs, berms, or ditches
placed around the work areas will adequately intercept surface water runoff.
Clearing and Stripping: After surface and near-surface water sources have been controlled, sod,
topsoil, and root-rich soil should be stripped from the site. Our subsurface explorations indicate
that there are minimal organic soils onsite below the asphalt pavement in the vicinity of the
proposed service bay addition but reaches thickness of upwards of 12 inches in the vicinity of the
new Brotherton Cadillac compound. Stripping is best performed during a period of dry weather.
Site Excavations: Based on our explorations, we expect that the vast majority of project
excavations will encounter poorly consolidated fine-grained alluvial soils, which can be readily
excavated utilizing standard excavation equipment.
Dewatering: Our explorations encountered groundwater in every subsurface boring at a depth of
approximately 8½ feet below the surface. We anticipate that an internal system of ditches, sump
holes, and pumps will be adequate to temporarily dewater shallow excavations. In order to
dewater deeper explorations below the regional water table, expensive dewatering equipment,
such as well points will need to be utilized.
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Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
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Temporary Cut Slopes: At this time, final designs and construction sequencing have not been
completed. To facilitate project planning we provide the following general comments regarding
temporary slopes:
• All temporary soil slopes associated with site cutting or excavations should be adequately
inclined to prevent sloughing and collapse,
• Temporary cut slopes in site soils should be no steeper than 1½H:1V, and
• Temporary slopes should conform to Washington Industrial Safety and Health Act
(WISHA) regulations.
These general guidelines are necessarily somewhat conservative (steeper temporary slopes may be
possible). As the project progresses, temporary grading plans are developed, final site features are
better defined, and a contractor is engaged, MGI may modify these general guidelines to allow
steeper slopes.
Subgrade Compaction: Exposed subgrades for the foundation of the proposed structures should
be compacted to a firm, unyielding state before new concrete or fill soils are placed. Any localized
zones of looser granular soils observed within a subgrade should be compacted to a density
commensurate with the surrounding soils. In contrast, any organic, soft, or pumping soils
observed within a subgrade should be overexcavated and replaced with a suitable structural fill
material.
Site Filling: Our conclusions regarding the reuse of onsite soils and our comments regarding wet-
weather filling are presented subsequently. Regardless of soil type, all fill should be placed and
compacted according to our recommendations presented in the Structural Fill section of this
report. Specifically, building pad fill soil should be compacted to a uniform density of at least
95 percent (based on ASTM:D-1557).
Onsite Soils: We offer the following evaluation of these onsite soils in relation to potential use as
structural fill:
• Alluvial Silt and Silty Sand: The alluvial silt and silty sand that underlies the site is very
moisture sensitive and will be difficult or impossible to reuse during most weather
conditions. It is currently above the optimum moisture content and will not compact
adequately unless aerated. Reuse is not recommended, and this material should only be
used for non-structural purposes, such as in landscaping areas.
• Alluvial Gravels: Encountered at intermediate and significant depths below ground
surface, this material is interbedded with its more fine-grained counterpart. Gravelly soils
which underlie the site are relatively impervious to moisture content variations and can be
reused as structural fill under most weather conditions.
Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to
reduce long-term raveling, sloughing, and erosion. We generally recommend that no permanent
slopes be steeper than 2H:1V. For all soil types, the use of flatter slopes (such as 2½H:1V) would
further reduce long-term erosion and facilitate revegetation.
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Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
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Slope Protection: We recommend that a permanent berm, swale, or curb be constructed along the
top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative groundcover
should be established as soon as feasible, to further protect the slopes from runoff water erosion.
Alternatively, permanent slopes could be armored with quarry spalls or a geosynthetic erosion
mat.
4.2 Spread Footings
In our opinion, conventional spread footings will provide adequate support for the proposed
structures if the subgrade is properly prepared. We offer the following comments and
recommendations for spread footing design.
Footing Depths and Widths: For frost and erosion protection, the bases of all exterior footings
should bear at least 18 inches below adjacent outside grades, whereas the bases of interior footings
need bear only 12 inches below the surrounding slab surface level. To reduce post-construction
settlements, continuous (wall) and isolated (column) footings should be at least 16 and 24 inches
wide, respectively.
Bearing Subgrades: Given the poor consolidation of near surface soil deposits in the vicinity of
the project area, structural fill bearing pads, 3 to 4 feet thick and compacted to a density of at least
95 percent (based on ASTM:D-1557), should underlie spread footings on this site. If foundation
construction occurs during wet conditions, it is possible that a geotextile fabric, placed between
the bearing pad and native soils, will be necessary. We should be consulted if any new
foundations are to be placed adjacent to existing foundations.
In general, before footing concrete is placed, any localized zones of loose soils exposed across the
footing subgrades should be compacted to a firm, unyielding condition, and any localized zones
of soft, organic, or debris-laden soils should be over-excavated and replaced with suitable
structural fill.
Lateral Overexcavations: Because foundation stresses are transferred outward as well as
downward into the bearing soils, all structural fill placed under footings, should extend
horizontally outward from the edge of each footing. This horizontal distance should be equal to
the depth of placed fill. Therefore, placed fill that extends 3 feet below the footing base should
also extend 3 feet outward from the footing edges.
Subgrade Observation: All footing subgrades should consist of firm, unyielding, native soils, or
structural fill materials that have been compacted to a density of at least 95 percent (based on
ASTM:D-1557). Footings should never be cast atop loose, soft, or frozen soil, slough, debris,
existing uncontrolled fill, or surfaces covered by standing water.
Bearing Pressures: In our opinion, for static loading, footings that bear on properly prepared,
structural fill bearing pads 3 feet thick can be designed for an allowable soil bearing pressure of
1,500 psf, and footings that bear on properly prepared, structural fill bearing pads 4 feet thick can
be designed for an allowable soil bearing pressure of 2,000 psf. A one-third increase in allowable
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 11 of 16
soil bearing capacity may be used for short-term loads created by seismic or wind related
activities.
Footing Settlements: Assuming that structural fill soils are compacted to a medium dense or
denser state, we estimate that total post-construction settlements of properly designed footings
bearing on properly prepared subgrades will not exceed 1 inch. Differential settlements for
comparably loaded elements may approach one-half of the actual total settlement over horizontal
distances of approximately 50 feet.
Footing Backfill: To provide erosion protection and lateral load resistance, we recommend that all
footing excavations be backfilled on both sides of the footings and stemwalls after the concrete has
cured. Either imported structural fill or non-organic onsite soils can be used for this purpose,
contingent on suitable moisture content at the time of placement. Regardless of soil type, all
footing backfill soil should be compacted to a density of at least 90 percent (based on ASTM:D-
1557).
Lateral Resistance: Footings that have been properly backfilled as recommended above will resist
lateral movements by means of passive earth pressure and base friction. We recommend using an
allowable passive earth pressure of 225 psf and an allowable base friction coefficient of 0.35 for
site soils.
4.3 Slab-On-Grade Floors
In our opinion, a soil-supported slab-on-grade floors can be used for the planned structures if the
subgrades are properly prepared. We offer the following comments and recommendations
concerning slab-on-grade floors.
Floor Subbase: Given the poor consolidation of near surface soil deposits in the vicinity of the
project area, we recommend over-excavation of slab-on-grade floor subgrades to a minimum
depth of 1½ feet, then placement of properly compacted structural fill as a floor subbase. If floor
construction occurs during wet conditions, it is likely that a geotextile fabric, placed between the
structural fill floor subbase and native soils, will be necessary. All subbase fill should be
compacted to a density of at least 95 percent (based on ASTM:D-1557).
Capillary Break and Vapor Barrier: To retard the upward wicking of moisture beneath the floor
slab, we recommend that a capillary break be placed over the subgrade. Ideally, this capillary
break would consist of a 4-inch-thick layer of pea gravel or other clean, uniform, well-rounded
gravel, such as “Gravel Backfill for Drains” per WSDOT Standard Specification 9-03.12(4), but
clean angular gravel can be used if it adequately prevents capillary wicking. In addition, a layer
of plastic sheeting (such as Crosstuff, Visqueen, or Moistop) should be placed over the capillary
break to serve as a vapor barrier. During subsequent casting of the concrete slab, the contractor
should exercise care to avoid puncturing this vapor barrier.
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 12 of 16
4.4 Subgrade and Retaining Walls
The following general recommendations should be applied to the design of subgrade and
retaining walls.
Wall Foundations: Subgrade and retaining wall foundations should be designed according to the
recommendations presented for spread footings in Section 4.2.
Wall Drainage: Drainage should be provided behind subgrade and retaining walls by placing a
zone of drain rock containing less than 3 percent fines (material passing No. 200 sieve) against the
wall. This drainage zone should be at least 24 inches wide (measured horizontally) and extend
from the base of the wall to within 1 foot of the finished grade behind the wall. Smooth-walled
perforated PVC drainpipe having a minimum diameter of 4 inches should be embedded within
the sand and gravel at the base of the wall along its entire length. This drainpipe should
discharge into a tight line leading to an appropriate collection and disposal system.
Backfill Soil: Ideally, all subgrade wall backfill would consist of clean, free-draining, granular
material, such as "Gravel Backfill for Walls" per WSDOT Standard Specification 9-03.12(2). A
geotextile should be placed between the drainage zone and the backfill soil to prevent drain
clogging.
Backfill Compaction: Because soil compactors place significant lateral pressures on subgrade
walls, we recommend that only small, hand-operated compaction equipment be used within 2 feet
of a backfilled wall. Also, all backfill should be compacted to a density as close as possible to
90 percent of the maximum dry density (based on ASTM:D-1557); a greater degree of compaction
closely behind the wall would increase the lateral earth pressure, whereas a lesser degree of
compaction might lead to excessive post-construction settlements.
Grading and Capping: To retard the infiltration of surface water into the backfill soils, we
recommend that the backfill surface of exterior walls be adequately sloped to drain away from the
wall. Ideally, the backfill surface directly behind the wall would be capped with asphalt, concrete,
or 12 inches of low-permeability (silty) soils to minimize or preclude surface water infiltration.
Applied Soil Pressure: Walls that are designed to move 0.1 percent of the wall height during and
after construction are usually referred to as unrestrained walls. We recommend that unrestrained
cantilever walls supporting slopes inclined at 2H:1V or flatter be designed to resist an active
pressure (triangular distribution) of 55 pounds per cubic foot (pcf) for drained conditions. The
recommended pressure does not include the effects of surcharges from surface loads, hydrostatic
pressures, or structural loads. If such surcharges are to apply, they should be added to the above
design lateral pressures. Traffic and vehicle loads may be modeled as an additional 2 feet of wall
height.
Wall Settlements: We estimate that the settlement of the wall footings constructed as
recommended will be on the order of 1 inch or less. Most of this settlement is expected to occur as
soon as the loads are applied. Differential settlement along the walls is expected to be 1 inch or
less over a 50-foot span.
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 13 of 16
4.5 Asphalt Pavement
Since pavements will be used for the new parking facilities and roadways, we offer the following
comments and recommendations for pavement design and construction.
Subgrade Preparation: We recommend over-excavation of pavement subgrades to depths of 12 or
24 inches, then placement of properly compacted structural fill as pavement subbase. If
construction occurs during wet conditions, it is likely that a geotextile fabric, placed between the
structural fill pavement subbase and native soils, will be necessary. We recommend a
conventional pavement section comprised of an asphalt concrete pavement over a crushed rock
base course over a properly prepared (compacted) subgrade or a granular subbase, depending on
subgrade conditions during pavement subgrade preparation.
All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded dump truck
or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling
operation should be over-excavated to a depth of 2 feet and replaced with a suitable structural fill
material. All structural fill should be compacted according to our recommendations given in the
Structural Fill section. Specifically, the upper 2 feet of soils underlying pavement section should
be compacted to at least 95 percent (based on ASTM D-1557), and all soils below 2 feet should be
compacted to at least 90 percent.
Pavement Materials: For the base course, we recommend using imported washed crushed rock,
such as "Crushed Surfacing Base Course” per WSDOT Standard Specification 9-03.9(3) but with a
fines content of less than 5 percent passing the No. 200 Sieve. Although our explorations do not
indicate a need for a pavement subbase, if a subbase course is needed, we recommend using
imported, clean, well-graded sand and gravel such as “Ballast” or “Gravel Borrow” per WSDOT
Standard Specifications 9-03.9(1) and 9-03.14, respectively.
Conventional Asphalt Sections: A conventional pavement section typically comprises an asphalt
concrete pavement over a crushed rock base course. We recommend using the following
conventional pavement sections:
Minimum Thickness
Pavement Course Parking Areas High Traffic Driveways
Asphalt Concrete Pavement 2 inches 4 inches
Crushed Rock Base 4 inches 8 inches
Granular Fill Subbase (if needed) 12 inches 24 inches
Concrete Pavement: We understand that concrete pavement will be placed at the site driveway,
along the access way, and as a pad for the backup generator. We recommend that concrete
pavements have a maximum thickness of 8 inches and be supported on prepared soil subgrades
and at least 4 inches of crushed rock base as recommended above.
Compaction and Observation: All subbase and base course material should be compacted to at
least 95 percent of the Modified Proctor maximum dry density (ASTM D-1557), and all asphalt
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 14 of 16
concrete should be compacted to at least 92 percent of the Rice value (ASTM D-2041). We
recommend that an MGI representative be retained to observe the compaction of each course
before any overlying layer is placed. For the subbase and pavement course, compaction is best
observed by means of frequent density testing. For the base course, methodology observations
and hand-probing are more appropriate than density testing.
Pavement Life and Maintenance: No asphalt pavement is maintenance-free. The above-described
pavement sections present our minimum recommendations for an average level of performance
during a 20-year design life; therefore, an average level of maintenance will likely be required.
Furthermore, a 20-year pavement life typically assumes that an overlay will be placed after about
10 years. Thicker asphalt and/or thicker base and subbase courses would offer better long-term
performance, but would cost more initially; thinner courses would be more susceptible to
“alligator” cracking and other failure modes. As such, pavement design can be considered a
compromise between a high initial cost and low maintenance costs versus a low initial cost and
higher maintenance costs.
4.6 Structural Fill
The term "structural fill" refers to any material placed under foundations, retaining walls, slab-on-
grade floors, sidewalks, pavements, and other structures. Our comments, conclusions, and
recommendations concerning structural fill are presented in the following paragraphs.
Materials: Typical structural fill materials include clean sand, gravel, pea gravel, washed rock,
crushed rock, well-graded mixtures of sand and gravel (commonly called "gravel borrow" or "pit-
run"), and miscellaneous mixtures of silt, sand, and gravel. Import materials meeting WSDOT
Standard Specification 9-03.14(1) gravel borrow will be satisfactory for use as structural fill during
dry weather. Recycled asphalt, concrete, and glass, which are derived from pulverizing the
parent materials, are also potentially useful as structural fill in certain applications. Soils used for
structural fill should not contain any organic matter or debris, nor any individual particles greater
than about 6 inches in diameter.
Fill Placement: Clean sand, gravel, crushed rock, soil mixtures, and recycled materials should be
placed in horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be
thoroughly compacted with a mechanical compactor.
Compaction Criteria: Using the Modified Proctor test (ASTM:D-1557) as a standard, we
recommend that structural fill used for various onsite applications be compacted to the following
minimum densities:
Fill Application Minimum
Compaction
Footing subgrade and bearing pad
Foundation backfill
Asphalt pavement base
Asphalt pavement subgrade (upper 2 feet)
Asphalt pavement subgrade (below 2 feet)
95 percent
90 percent
95 percent
95 percent
90 percent
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
Brotherton Buick GMC – Brotherton Cadillac Auto Dealership, 215 SW 12th St, Renton, WA July 8, 2021
Geotechnical Engineering Report P2411-T21
Migizi Group, Inc. Page 15 of 16
Subgrade Observation and Compaction Testing: Regardless of material or location, all structural
fill should be placed over firm, unyielding subgrades prepared in accordance with the Site
Preparation section of this report. The condition of all subgrades should be observed by
geotechnical personnel before filling or construction begins. Also, fill soil compaction should be
verified by means of in-place density tests performed during fill placement so that adequacy of
soil compaction efforts may be evaluated as earthwork progresses.
Soil Moisture Considerations: The suitability of soils used for structural fill depends primarily on
their grain-size distribution and moisture content when they are placed. As the "fines" content
(that soil fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small
changes in moisture content. Soils containing more than about 5 percent fines (by weight) cannot
be consistently compacted to a firm, unyielding condition when the moisture content is more than
2 percentage points above or below optimum. For fill placement during wet-weather site work,
we recommend using "clean" fill, which refers to soils that have a fines content of 5 percent or less
(by weight) based on the soil fraction passing the U.S. No. 4 Sieve.
5.0 RECOMMENDED ADDITIONAL SERVICES
Because the future performance and integrity of the structural elements will depend largely on
proper site preparation, drainage, fill placement, and construction procedures, monitoring and
testing by experienced geotechnical personnel should be considered an integral part of the
construction process. Subsequently, we recommend that MGI be retained to provide the
following post-report services:
• Review all construction plans and specifications to verify that our design criteria
presented in this report have been properly integrated into the design,
• Prepare a letter summarizing all review comments (if required),
• Check all completed subgrades for footings and slab-on-grade floors before concrete is
poured, in order to verify their bearing capacity, and
• Prepare a post-construction letter summarizing all field observations, inspections, and test
results (if required).
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
APPROXIMATE SITE
LOCATION
P.O. Box 44840
Tacoma, WA 98448
Location Job Number Figure
DateTitle
215 SW 12th St
Renton, WA
Topographic and Location Map
1
07/08/21
P2411-T21
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
APPENDIX A
SOIL CLASSIFICATION CHART AND
KEY TO TEST DATA
LOGS OF BORINGS
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
CLAYEY GRAVELS, POORLY GRADED GRAVEL-SAND-CLAY
MIXTURES
SILTS AND CLAYSCOARSE GRAINED SOILSMore than Half > #200 sieveLIQUID LIMIT LESS THAN 50
LIQUID LIMIT GREATER THAN 50
CLEAN GRAVELS
WITH LITTLE OR
NO FINES
GRAVELS WITH
OVER 15% FINES
CLEAN SANDS
WITH LITTLE
OR NO FINES
MORE THAN HALF
COARSE FRACTION
IS SMALLER THAN
NO. 4 SIEVE
MORE THAN HALF
COARSE FRACTION
IS LARGER THAN
NO. 4 SIEVE
INORGANIC SILTS, MICACEOUS OR DIATOMACIOUS FINE
SANDY OR SILTY SOILS, ELASTIC SILTS
ORGANIC CLAYS AND ORGANIC SILTY CLAYS OF LOW
PLASTICITY
OH
INORGANIC SILTS AND VERY FINE SANDS, ROCK FLOUR,
SILTY OR CLAYEY FINE SANDS, OR CLAYEY SILTS WITH
SLIGHT PLASTICITY
CH
SILTY GRAVELS, POORLY GRADED GRAVEL-SAND-SILT
MIXTURES
SANDS
SILTS AND CLAYS
Figure A-1
INORGANIC CLAYS OF LOW TO MEDIUM PLASTICITY,
GRAVELLY CLAYS, SANDY CLAYS, SILTY CLAYS,
LEAN CLAYS
R-Value
Sieve Analysis
Swell Test
Cyclic Triaxial
Unconsolidated Undrained Triaxial
Torvane Shear
Unconfined Compression
(Shear Strength, ksf)
Wash Analysis
(with % Passing No. 200 Sieve)
Water Level at Time of Drilling
Water Level after Drilling(with date measured)
RV
SA
SW
TC
TX
TV
UC
(1.2)
WA
(20)
Modified California
Split Spoon
Pushed Shelby Tube
Auger Cuttings
Grab Sample
Sample Attempt with No Recovery
Chemical Analysis
Consolidation
Compaction
Direct Shear
Permeability
Pocket Penetrometer
CA
CN
CP
DS
PM
PP
PtHIGHLY ORGANIC SOILS
TYPICAL NAMES
GRAVELS
ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY,
ORGANIC SILTS
WELL GRADED GRAVELS, GRAVEL-SAND MIXTURES
MAJOR DIVISIONS
PEAT AND OTHER HIGHLY ORGANIC SOILS
WELL GRADED SANDS, GRAVELLY SANDS
POORLY GRADED SANDS, GRAVELLY SANDS
SILTY SANDS, POORLY GRADED SAND-SILT MIXTURES
CLAYEY SANDS, POORLY GRADED SAND-CLAY MIXTURES
POORLY GRADED GRAVELS, GRAVEL-SAND MIXTURES
SOIL CLASSIFICATION CHART AND KEY TO TEST DATA
GW
GP
GM
GC
SW
SP
SM
SC
ML
FINE GRAINED SOILSMore than Half < #200 sieveLGD A NNNN02 GINT US LAB.GPJ 11/4/05INORGANIC CLAYS OF HIGH PLASTICITY, FAT CLAYS
CL
OL
MH
SANDS WITH
OVER 15% FINES
Migizi Group, Inc.
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
SS
S-1
SS
S-2
SS
S-3
SS
S-4
SS
S-5
SS
S-6
SS
S-7
SS
S-8
SS
S-9
11
11
11
18
9
16
9
6
12
4-6-6
(12)
14-16-20
(36)
9-10-11
(21)
10-26-26
(52)
14-14-18
(32)
8-1-1
(2)
10-16-12
(28)
10-13-20
(33)
8-10-14
(24)
GP-
GM
SP-
SM
ML
SP-
SM
GP-
GM
GP
ML
GP
0.3
1.0
2.0
5.0
7.5
10.0
20.5
25.0
36.5
3 inches asphaltic concrete
(GP-GM) Gray gravel with silt and fine to coarse sand (medium dense, moist) (crushed rock)
(SP-SM) Light brown fine to medium sand with silt and gravel (medium dense, moist) (Fill)
(ML) Dark gray silt (firm, moist)
(SP-SM) Gray/brown fine to medium sand with silt and gravel (dense, moist)
(GP-GM) Gray/brown gravel with silt and fine to coarse sand (medium dense, wet)
(GP) Gray/brown gravel with fine to coarse sand (very dense, wet)
Grades to dense
(ML) Dark gray silt (very soft, wet)
(GP) Gray/brown gravel with fine to coarse sand (medium dense, wet)
Grades to dense
Grades to medium dense
Bottom of borehole at 36.5 feet.
NOTES
LOGGED BY ZLL
DRILLING METHOD Truck Mounted Drill Rig
DRILLING CONTRACTOR Holocene Drilling Inc.GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 4/26/21 COMPLETED 4/26/21
AT TIME OF DRILLING 8.50 ft
AT END OF DRILLING ---
AFTER DRILLING ---
HOLE SIZE 4.25" HSAGROUND ELEVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
10
15
20
25
30
35
PAGE 1 OF 1
Figure A-2
BORING NUMBER B-1
CLIENT Brotherton Buick GMC
PROJECT NUMBER P2411-T21
PROJECT NAME Brotherton Cadillac Auto Dealership Geotech
PROJECT LOCATION 215 SW 12th St, Renton, WA
COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 6/18/21 22:22 - C:\USERS\JESSICABIZAK\DESKTOP\TEST PITS AND BORINGS - GINT\P2411-T21\P2411-T21 BORING LOGS.GPJMigizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RECOVERY (in)(RQD)BLOWCOUNTS(N VALUE)U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
SS
S-1
SS
S-2
SS
S-3
SS
S-4
SS
S-5
SS
S-6
SS
S-7
SS
S-8
SS
S-9
12
6
12
12
0
18
6
12
18
4-4-3
(7)
2-3-2
(5)
11-12-14
(26)
7-10-9
(19)
0-0-1
(1)
1-2-2
(4)
3-4-7
(11)
10-16-18
(34)
6-19-27
(46)
GP-
GM
SM
GP-
GM
ML
ML
ML
GP
0.3
1.0
6.5
15.0
20.0
25.0
30.0
36.5
3 inches asphaltic concrete
(GP-GM) Gray gravel with silt and fine to coarse sand (medium dense, moist) (crushed rock)
(SM) Gray/brown silty sand with some gravel (loose, moist)
(GP-GM) Light brown gravel with silt and fine to coarse sand (medium dense, wet)
(ML) No recovery
Blue/gray silt (very soft, wet)
(ML) Gray/brown silt with abundant organics (very soft, wet)
(ML) Gray/brown silt (firm, wet)
(GP) Gray gravel with fine to coarse sand (dense, wet)
Bottom of borehole at 36.5 feet.
NOTES
LOGGED BY ZLL
DRILLING METHOD Truck Mounted Drill Rig
DRILLING CONTRACTOR Holocene Drilling Inc.GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 4/26/21 COMPLETED 4/26/21
AT TIME OF DRILLING 8.50 ft
AT END OF DRILLING ---
AFTER DRILLING ---
HOLE SIZE 4.25" HSAGROUND ELEVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
10
15
20
25
30
35
PAGE 1 OF 1
Figure A-3
BORING NUMBER B-2
CLIENT Brotherton Buick GMC
PROJECT NUMBER P2411-T21
PROJECT NAME Brotherton Cadillac Auto Dealership Geotech
PROJECT LOCATION 215 SW 12th St, Renton, WA
COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 6/18/21 22:22 - C:\USERS\JESSICABIZAK\DESKTOP\TEST PITS AND BORINGS - GINT\P2411-T21\P2411-T21 BORING LOGS.GPJMigizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RECOVERY (in)(RQD)BLOWCOUNTS(N VALUE)U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08
SS
S-1
SS
S-2
SS
S-3
SS
S-4
SS
S-5
SS
S-6
SS
S-7
SS
S-8
SS
S-9
6
0
12
12
12
9
9
9
12
3-0-2
(2)
2-0-1
(1)
4-4-6
(10)
4-7-8
(15)
7-9-11
(20)
2-3-4
(7)
7-12-13
(25)
16-30-28
(58)
6-22-23
(45)
SM
GP-
GM
ML
GP-
GM
GP
SM
GP
1.0
3.5
5.0
8.0
15.0
20.0
25.0
36.5
Sod and topsoil
(SM) Brown silty sand with gravel (very loose, moist)
(GP-GM) Light brown gravel with silt and fine to coarse sand (very loose, moist)
(ML) No recovery
Dark gray silt with some organics (very soft, wet)
(GP-GM) Light brown gravel with silt and fine to coarse sand (medium dense, moist)
(GP) Light brown gravel with fine to coarse sand (medium dense, moist)
(SM) Blue/gray silty sand (loose, wet)
(GP) Gray gravel with fine to coarse sand (medium dense, wet)
Grades to very dense
Grades to dense
Bottom of borehole at 36.5 feet.
NOTES
LOGGED BY ZLL
DRILLING METHOD Truck Mounted Drill Rig
DRILLING CONTRACTOR Holocene Drilling Inc.GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 4/26/21 COMPLETED 4/26/21
AT TIME OF DRILLING 8.50 ft
AT END OF DRILLING ---
AFTER DRILLING ---
HOLE SIZE 4.25" HSAGROUND ELEVATION
SAMPLE TYPENUMBERDEPTH(ft)0
5
10
15
20
25
30
35
PAGE 1 OF 1
Figure A-4
BORING NUMBER B-3
CLIENT Brotherton Buick GMC
PROJECT NUMBER P2411-T21
PROJECT NAME Brotherton Cadillac Auto Dealership Geotech
PROJECT LOCATION 215 SW 12th St, Renton, WA
COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 6/18/21 22:22 - C:\USERS\JESSICABIZAK\DESKTOP\TEST PITS AND BORINGS - GINT\P2411-T21\P2411-T21 BORING LOGS.GPJMigizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
RECOVERY (in)(RQD)BLOWCOUNTS(N VALUE)U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
DocuSign Envelope ID: 206613E4-C662-427B-B5B2-D00F0C51DB08