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GEOTECHNICAL ENGINEERING
DESIGN REPORT
3123 Sunset Blvd NE
Renton, WA 98056
Prepared for: Carson AuYeung
Livia Chen
Job No: 1054-KIN
Chris J. Heathman, P.E.
Principle Geotechnical Engineer
Mud Bay Geotechnical Services, LLC
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Table of Contents
1. Introduction ....................................................................................................................... 1
1.1. General ........................................................................................................................ 1
1.2. Location and Description.............................................................................................. 1
2. Site Conditions .................................................................................................................. 1
2.1. Site Soils and Geology ................................................................................................. 1
2.2. Subsurface and Groundwater Conditions ..................................................................... 1
2.2.1. On-Site Soils ......................................................................................................... 1
2.2.2. Surface Water and Groundwater........................................................................... 2
3. Geologic Hazards .............................................................................................................. 2
3.1. Liquefaction Potential ................................................................................................... 2
3.2. Fault Rupture Hazard ................................................................................................... 2
4. Geotechnical Recommendations ..................................................................................... 3
4.1. Seismic Design ............................................................................................................ 3
4.2. Shallow Foundation Design and Construction .............................................................. 3
4.2.1. Shallow Foundation Support ................................................................................. 3
4.2.2 Lateral Earth Pressures ............................................................................................ 4
4.2.3. Slab-On-Grade Support ............................................................................................ 4
4.2.4. Foundation Drainage Considerations ........................................................................ 5
4.3. Utilities ......................................................................................................................... 5
4.4. Earthwork Considerations ............................................................................................ 5
4.4.1. Structural Fill ......................................................................................................... 5
4.4.2. Site Grading .......................................................................................................... 6
4.5. Temporary Slopes and Structural Shoring ................................................................... 6
5. Recommended Additional Services ................................................................................ 6
6. Intended Use and Limitations .......................................................................................... 6
7. References ........................................................................................................................ 7
LIST OF APPENDICES
Appendix A – Field Exploration Program
LIST OF FIGURES
Figure 1 – Site Map
Figure 2 – Site Plan
Figure 3 – USDA Soil Map
Figure 4 – Geologic Map
Figure 5 – Site Exploration Map
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LIST OF TABLES
Table 1: Seismic Design Parameters ......................................................................................... 3
Table 2: Lateral Earth Pressure Parameters ............................................................... ………….4
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1. Introduction
1.1. General
This report presents the results of our geotechnical investigation and contains geotechnical
recommendations for the project taking place at 3123 Sunset Blvd NE, Renton WA 98056.
The analyses, conclusions, and recommendations in this report are based on one boring
(designated as BH-1-19) completed specifically for this project, published geologic information for
the site and vicinity and our experience with similar geologic materials. The conditions observed
in the bore hole are assumed to be representative of the subsurface conditions throughout the
project area. If during construction, subsurface conditions differ from those described in the
explorations, we should be advised immediately so we may reevaluate the recommendations.
1.2. Location and Description
The parcel is located at 3123 Sunset Blvd NE in Renton, WA. The site location and vicinity
for the property are presented in Figure 1. The site has a history of previous development,
which included a commercial building structure and pavement surface surrounding the building.
The building was recently demolished, and the entire building and pavement was removed
and cleared down to bare earth. The perimeter of the site facing Sunset Blvd NE and NE 12th
St are landscaped with small bushes and shrubs interrupted by driveway access points.
The scope of the project is to develop the site with an 8,000 to 10,000 SF, 2 to 3-story structure
with ground floor to be used for commercial use as a daycare facility. It’s anticipated the structure
will be supported on shallow strip footing foundations. The lowermost story may be a below
ground basement level for additional parking. The existing property is graded at a relatively flat
slope angle. An on-site treatment may be necessary, if infiltration testing and recommendations
are required then it will be addressed in a separate report and is not within the scope of this report.
2. Site Conditions
2.1. Site Soils and Geology
As part of this project, we reviewed available geologic data from the USDA Soil Conservation
Survey and the Washington State Department of Natural Resources and prepared site-specific
geology and soils maps, which are attached as Figures 3 and 4, respectively. The USDA Soil
Conservation Survey map indicates the surface soils at the site consist of Arents, Alderwood
Material, 6 to 15 percent slope. It should be noted the percent slope in these descriptions is an
approximation. The project vicinity geologic map indicates the project site is underlain by
Pleistocene Continental Glacial Till. The conditions in the explorations are generally consistent
with the mapped soils and geology at the site.
2.2. Subsurface and Groundwater Conditions
2.2.1. On-Site Soils
A single hand auger boring, designated BH-1-19, was performed to explore the subsurface
conditions at the site location. The approximate location of the boring is shown on Figure 5. Based
on the conditions observed in the boring, the soils at the site generally consist of moist, brownish
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gray, gravelly sand. The upper 18 inches of soil is relatively loose due to the recent disturbance
from demolition activities. The material below 18 inches deep is very dense based on the difficulty
of advancing the hole. More detailed information regarding site soil conditions and a description
of our field exploration and procedures is included in Appendix A.
2.2.2. Surface Water and Groundwater
Groundwater was not encountered in boring BH-1-19. It’s not anticipated significant groundwater
is present within the limits of the excavation to be performed as part of the construction of the
project. However, based on the heterogeneous nature of the native glacial till, it is possible small
pockets of perched groundwater will be encountered. Localized seepage is common within lenses
of coarser grained sand and gravel contained in Pleistocene continental glacial till deposits
mapped at the site. Localized seepage typically occurs in areas where coarser soils such as
sands and gravels are trapped within finer grained silts and clays. The groundwater seepage
within these trapped zones generally will not result in surface water seepage until exposed either
through excavation cuts during construction or through natural erosion processes.
There are no notable natural surface water bodies within the site vicinity. The site is in an urban
environment with a significant amount of impervious surface. Surface water runoff from storm
events directly falling onto the ground in this type of environment is generally collected and
directed to detention or infiltration facilities such as swales and ponds, or to catch basins and
conveyed through underground stormwater sewer facilities to an appropriate discharge location.
A small amount of surface water will infiltrate into the ground within landscaped areas and green
space.
3. Geologic Hazards
3.1. Liquefaction Potential
Soil liquefaction is a phenomenon whereby saturated soil deposits temporarily lose strength and
behave as a viscous fluid in response to cyclic loading. Soil types considered at the highest risk
of liquefaction during a seismic event are loose sandy soils. Gravel material can be susceptible
to liquefaction if it contains a significant fraction of sand-sized particles and is capped by less
permeable material. Groundwater was not encountered in boring BH-1-19 to a depth of 7 feet.
Furthermore, the site soils are not considered susceptible to liquefaction based on their high
relative density and limited potential for groundwater at shallow depths, and therefore liquefaction
is not a design consideration for this project.
3.2. Fault Rupture Hazard
The potential impacts of fault rupture include abrupt, large, differential ground movement and
associated damage to structures that might straddle the fault. The nearest active crustal fault is
the Seattle Fault system. The closest mapped fault splay associated with the Seattle Fault system
is located approximately 1.5 to 2.0 miles away from the project site. In our opinion, the risk of fault
rupture at the site is low.
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4. Geotechnical Recommendations
4.1. Seismic Design
Seismic design should be performed based on the design criteria and hazard maps in the 2015
International Building Code (IBC, 2015) for peak ground acceleration (PGA) at the site location
based on the United States Geological Survey hazard maps for the 2,475 year recurrence interval
at the site location (Peterson et. al, 2014). Adjustment factors should be applied to account for
amplification as ground motions transmit from the bedrock surface up through the soil column to
the ground surface. For design purposes, we recommend assuming Site Class D soils. Seismic
design parameters for the site location are provided in Table 1.
Table 1: Seismic Design Parameter s
Site Class based on soil conditions Site Class = D
Peak Horizontal ground acceleration coefficient on Class B rock PGA = 0.61
Site coefficient for the peak ground acceleration coefficient FPGA = 1.1
Effective peak ground acceleration coefficient (g) As=FPGA(PGA)= 0.67
4.2. Shallow Foundation Design and Construction
4.2.1. Shallow Foundation Support
The site development of the parcel includes an 8,000 to 10,000 SF, 2 to 3-story structure with
ground floor to be used for commercial use as a daycare facility. We anticipate that the structure
will be supported on shallow strip footing foundations. In addition, the lowermost story may be a
below ground basement level for parking. Shallow strip footings will be used to support the
structure loads. We anticipate the footings will be supported on native glacial till soils. Prior to
construction of the footings, the subgrade should be cleared and grubbed and the exposed native
subgrade soils should be compacted in place. The subgrade should be inspected for any pockets
of loose material. Loose material should be removed and replaced with a minimum of 6-inches of
Crushed Surfacing Base Course (CSBC) meeting the requirements of Section 9-03.9(3) of the
WSDOT Standard Specifications (WSDOT, 2018) or an equivalent material.
The CSBC should be placed in layers no greater than 6-inches and compacted to at least 95
percent of the maximum dry density. Footings bearing on a subgrade prepared as described
above can be designed using a maximum allowable bearing pressure of 3,500 psf. The maximum
allowable bearing pressure may be increased by up to one-third for short-term transient loading
conditions such as wind and seismic loading. We anticipate the total settlement will not exceed
one inch, and differential settlement along a 50-foot length will not exceed half of the total
settlement. The settlement is expected to be elastic and will occur as the footings are loaded.
We recommend footing subgrade preparation be evaluated by Mud Bay Geotechnical Services,
LLC prior to placement of concrete. Foundation subgrade preparation should not be performed
during periods of wet weather. We recommend staging the foundation subgrade excavation,
compaction of native subgrade soils, and placement of CSBC to limit the time the foundation
subgrade is exposed to weather.
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4.2.2 Lateral Earth Pressures
Retaining walls or stem walls should be designed to resist lateral earth pressures of the backfill
placed behind the walls. For lateral load analysis, we recommend the geotechnical parameters in
Table 2 be used for lateral design and analysis.
Backfill behind the walls should be placed in horizontal layers no more than 6 inches thick with
each layer compacted to 95 percent of the maximum density. The backfill material should be
comprised of Gravel Backfill for Walls material meeting the requirements of Section 9-03.12(2) of
the WSDOT Standard Specifications (WSDOT, 2018), or an equivalent free-draining material.
Table 2: Lateral Earth Pressure Parameters
Parameter Design Value
Backfill Unit Weight (γ) 135 pcf
Wall Backfill Soil Friction Angle (φf) 37°
Coefficient of Sliding (tan φf) 0.55
Active Earth Pressure (Ka) 0.23 (EFP 31.1 psf)
At Rest Earth Pressure (K0) 0.40 (EFP 54.0 psf)
Passive Earth Pressure (Kp) 8.78 (EFP 1,185 psf)
The passive earth pressure coefficient and coefficient of sliding presented in Table 2 are ultimate
values and should be reduced by a factor of safety equal to 1.5 for final design. The lateral earth
pressure coefficients provided in Table 2 are based on the use of Gravel Backfill for Walls. Active
earth pressures can be assumed for design, provided that the walls can yield laterally at least
0.001H (where H is the exposed wall height in feet). If the wall is not capable of yielding that
amount, then at-rest earth pressures should be used.
Seismic loading represented as a rectangular shaped dynamic uniform lateral surcharge equal to
8H psf should be applied, with the resultant acting at a height of 0.5H, where H is the height of
the wall. This value, which was calculated using the Mononobe-Okabe method, is appropriate for
yielding walls designed in accordance with the 2015 IBC (IBC, 2015).
4.2.3. Slab-On-Grade Support
All interior slabs-on-grade should be underlain by a capillary break at least 6 inches thick
consisting of free-draining, clean, course sand and fine gravel with a maximum particle size of ¾-
inch, no more than 50 percent passing the U.S. No. 4 sieve, and less than 5 percent passing the
U.S. No. 200 sieve.
Prior to placement of the capillary break layer, topsoil, mud, debris, and rootmass should be
cleared and grubbed and the native subgrade soils should be compacted in-place to a dense and
relatively unyielding condition. The six-inch capillary break layer should be compacted to at least
95 percent of the maximum dry density of the material. We recommend considering placement of
a suitable vapor barrier to further retard moisture at the slab-on-grade.
Similar to footing construction, it will be helpful to stage the excavation and subgrade preparation
of slab-on-grade areas to limit the exposure to wet weather placement of the capillary break layer.
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Once in place and compacted, the low-fines-content capillary break layer will reduce the likelihood
that the subgrade is disturbed.
We recommend using a vertical modulus (Kv1) of 85 pounds per cubic inch (pci) for slab-on- grade
bearing on a subgrade prepared as described above. Note that Kv1 is appropriate for a 1-foot by
1-foot surface and the initial subgrade modulus used for design (Ks) will need to be adjusted based
on the width of the footing or slab considered using the following equation:
Ks = Kv1(B+1)2/(4B2)
where B = foundation or slab width in feet.
4.2.4. Foundation Drainage Considerations
It’s recommended including a perimeter footing drain system, consisting of a 4-inch diameter,
perforated or slotted, rigid plastic pipe placed at the base of the wall footings. The drain should
be embedded in a clean, free-draining sand and gravel meeting the requirements of Section 9-
03.12(4) of the WSDOT Standard Specifications for Gravel Backfill for Drains. The drains should
be sloped slightly to drain to an appropriate discharge area. Appropriate water and weather
proofing measures should be used in order to reduce the potential for leaks through the basement
walls.
4.3. Utilities
We anticipate that buried utilities will need to be constructed as part of the project. The utility
subgrade (base of trench excavation) should be relatively firm prior to placing bedding materials.
Subgrade observed to be soft, pumping, or containing abundant organics or refuse should be
sub-excavated to firm subgrade soil or a maximum depth of 2 feet. Sub-excavated areas should
be backfilled with structural fill.
Material placed directly below, around, and above utility pipes should consist of Gravel Backfill
for Pipe Zone Bedding as described in Section 9-03.12(3) of the WSDOT Standard Specifications
(WSDOT, 2018). The pipe bedding materials should be placed and compacted to a relatively firm
condition in accordance with the manufacturer’s specifications. Bedding and cover should be a
minimum of 6-inches thick.
4.4. Earthwork Considerations
4.4.1. Structural Fill
Soils placed as fill beyond the limits of foundation subgrade, wall backfill, and pipe zone areas
described previously should be considered structural fill. Structural fill should consist of material
meeting the requirements of Common Borrow as described in Section 9-03.14(3) of the WSDOT
Standard Specifications (WSDOT, 2018). Based on the conditions observed in boring BH-1-19,
the onsite material to be removed for construction meets the requirements for Common Borrow.
Structural fill should be placed and compacted in lifts no greater than 8 inches when using
relatively large compaction equipment, such as a vibrating compaction equipment attached to an
excavator or a drum roller. If small, hand-operated compaction equipment is used to compact the
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structural fill, fill lifts should not exceed 6 inches. Based on the small size of the project and difficult
access, most likely relatively large compaction equipment will be used.
Structural fill should be placed and compacted to between 90 and 92 percent of the maximum dry
density. All other fill material should be placed and compacted as described previously. Fill placed
in softscape, landscape, or common areas that can accommodate some settlement should be
compacted to a relatively firm and unyielding condition.
4.4.2. Site Grading
We recommend grading all permanent cuts and fills to a maximum slope angle of 2H:1V. Until a
layer of vegetation is established, the upper 1 to 2 feet below the surface of the slope may be only
marginally stable. To reduce the potential for short term erosion, coir, jute, or turf reinforcement
mat should be placed on the surface of the slope until vegetation is established.
4.5. Temporary Slopes and Structural Shoring
Stability for all other temporary excavation slopes, structural shoring, and temporary works
necessary to complete the project not shown in the plans for the project remain the responsibility
of the Contractor. The Contractor will determine the appropriate measures to ensure all
excavation is in compliance with local, state and federal safety codes. Washington Administrative
Code 296-155 (WAC, 2009) contains specific requirements for trenches and temporary slopes.
For planning and cost estimating purposes, we recommend assuming 1H:1V temporary slopes
are feasible.
5. Recommended Additional Services
Before construction begins, we recommend a copy of the draft plans and specifications prepared
for the project be made available for review so we can ensure the geotechnical recommendations
in this report are included in the Contract.
Mud Bay Geotechnical Services, LLC is also available to provide geotechnical engineering and
construction monitoring services throughout the remainder of the design and construction of t he
project. The integrity of the geotechnical elements of a project depend on proper site preparation
and construction procedures. In addition, engineering decisions may need to be made in the field
if conditions are encountered differ from those described in this report.
During the construction phase of the project, we recommend Mud Bay Geotechnical Services,
LLC be retained to review construction submittals, observe and evaluate subgrade for all slabs-
on-grade and footings, and provide recommendations for any other geotechnical considerations
that may arise during construction.
6. Intended Use and Limitations
This report has been prepared to assist the client and their consultants in the engineering design
and construction of the subject project. It should not be used, in part or in whole for other purposes
without contacting Mud Bay Geotechnical Services, LLC for a review of the applicability of such
reuse. This report should be made available to prospective contractors for their information only
and not as a warranty of ground conditions.
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The conclusions and recommendations contained in this report are based on Mud Bay
Geotechnical Services, LLC understanding of the project at the time the report was written and
on-site conditions existing at time of the field exploration. If significant changes to the nature,
configuration, or scope of the project occur during the design process, we should be consulted to
determine the impact of such changes on the recommendations and conclusions presented in
this report.
Site exploration and testing describes subsurface conditions only at the sites of subsurface
exploration and at the intervals where samples are collected. These data are interpreted by Mud
Bay Geotechnical Services, LLC rendering an opinion regarding the general subsurface
conditions. Actual subsurface conditions can be discovered only during earthwork and
construction operations. The distribution, continuity, thickness, and characteristics of identified
(and unidentified) subsurface materials may vary considerably from that indicated by the
subsurface data. While nothing can be done to prevent such variability, Mud Bay Geotechnical
Services, LLC is prepared to work with the project team to reduce the impacts of variability on
project design, construction, and performance.
We appreciate the opportunity to serve your geotechnical needs on this project, and look forward
to working with you in the future. Please contact us at your earliest convenience if you have any
questions or would like to discuss the contents of this report.
7. References
International Building Code (IBC), 2015, International Building Code, prepared by International
Code Council.
Petersen, M.D., et al., 2014, Documentation for the 2014 update of the United States national
seismic hazard maps: U.S. Geological Survey Open-File Report 2014–1091, 243 p.,
https://dx.doi.org/10.3133/ofr20141091.
Washington Administrative Code (WAC), 2009, April 1, 2009.
Washington Department of Natural Resources Division of Geology and Earth Resources (DNR),
2016, https://geologyportal.dnr.wa.gov, accessed 8/26/2018 06:05 PM.
Washington State Department of Transportation (WSDOT), 2015, Geotechnical Design Manual,
Washington State Department of Transportation, Olympia WA. (www.wsdot.wa.gov/
Publications/Manuals/M46-03.htm)
Washington State Department of Transportation (WSDOT), 2018, Standard Specifications for
Road, Bridge, and Municipal Construction, Washington State Department of Transportation,
Olympia WA. (www.wsdot.wa.gov/Publications/Manuals/M41-10.htm)
Site Location
Figure 1: Site Map
3123 NE Sunset Blvd,
Renton, WA 98056
Site Development Geotechnical Report
JOB #: 1054-KIN Date: March, 2019
Figure 2: Site Plan
3123 NE Sunset Blvd,
Renton, WA 98056
Site Development Geotechnical Report
JOB #: 1054-KIN Date: March, 2019
LEGEND
Site Location
Figure 2: Geology Map
216 9th Ave SE
Olympia, WA 98501
Seismic Retrofit Geotechnical Report
JOB #: 1040-THU Date: February, 2018
Figure 3: Geologic Map
3123 NE Sunset Blvd,
Renton, WA 98056
Site Development Geotechnical Report
JOB #: 1054-KIN Date: March, 2019
Sources: City of Olympia, Bureau of Land Management, Esri,
HERE, Garmin, INCREMENT P, NGA, USGS | Washington
Division of Geology and Earth Resources
Sources: City of Renton, County of King, Bureau of Land Management, Esri,
HERE, Garmin, INCREMENT P, NGA, USGS | Washington Division of Geology
and Earth Resources
N
Legend
Site location
AmC Arents, Alderwood material, 6 to 15
percent slopes
Ur Urban land
Figure 4: USDA Soil Map
3123 NE Sunset Blvd,
Renton, WA 98056
Site Development Geotechnical Report
JOB #: 1054-KIN Date: March, 2019
Sample Collection Location
BH-1-19
N
JOB #: 1054-KIN Date: March, 2019
Figure 5: Site Exploration Map
3123 NE Sunset Blvd,
Renton, WA 98056
Site Development Geotechnical Report
APPENDIX A – FIELD EXPLORATION PROGRAM
FIELD EXPLORATION PROGRAM
To characterize the surface and subsurface conditions for the project, Mud Bay Geotechnical
Services, LLC performed a single boring, designated BH-1-19. The boring was completed from
the existing ground surface at the approximate location shown on Figure 5.
The boring was completed using a Humboldt Manufacturing model H-4206.6A hand auger with
a 3 ¼ inch diameter bucket tube sampler. A prybar was used at selected locations to break up
some of the gravel particles in order to facilitate advancing the hole.
The soil samples were classified visually in the field in general accordance with ASTM D2488,
the Standard Practice for Description and Identification of Soils (Visual-Manual Procedure).
Once transported back to the office, the samples were re-examined and the field classifications
were modified accordingly. A summary log of the boring is included in Appendix A. Note the soil
descriptions and interfaces shown on the log are interpretive, and actual changes may be
gradual. Upon completion, the hole was backfilled to the original ground surface using
excavated material from the spoil pile.
Completed:Hammer Type:
Backfilled:Hammer Weight:Hammer Drop:
Groundwater Depth:Total Depth of Boring:
Lithology
Note: the upper 18" was made up of construction overburden
Moist, brownish gray, gravelly sand, with med grain gravels, (SW)
Moist, brownish gray, gravelly sand, with med grain gravels, (SW)
Standard Penetration Slit Spoon Sampler (SPT)
Blows/3/4"Density
0-4 Very Loose
5-10 Loose
11-24 Medium Dense
25-50 Dense
>50 Vey Dense
REF Refusal Moisture Content (%)Additional TestSoil Group Name: modifier, color, moisture, density/consistency, grain size, other
descriptors
Rock Description: modifierm color, hardness/degree of concentration, bedding and
joint characteristics, solutions, void conditions.Graphic LogDateSite Development
3/1/2019
Address:Started:
Logan Krehbiel
3123 Sunset Blvd, Renton
WA 98056
Project Number:
1054-KIN
Gravel, Sand, Non-Plastic Silt Elastic Silts and Clays
Bailly & Bailly LLC BH-1-19
3/1/2019
3/1/2019
n/a Hand Auger
n/a
Dry Density (pcf)Client:Boring No. 1 of 2:
Drilling Contractor:Drill Rig Type:
3.25 inches
Steel n/a
Soil Density Modifiers
Bit Type:Diameter:
Fluid:
none
Elevation:
Existing Surface 84"
n/a n/a
Bore Log Symbols
Logged By:
Samantha Denham
Drill Crew:
Project:Depth (feet)Sample TypeSample NumberBlow Counts (blows/3/4")California Sampler
Shelby Tube
CPP Sampler
StabIlized Ground water
Groundwater At time of Drilling
Bulk/ Bag Sample
Blows/3/4"
0-1
2-4
5-8
9-15
16-30
31-61
Very Stiff
31-60
Consistency
Very Soft
Soft
Medium Stiff
Stiff
Hard
Very Hard
3
6
S-1
S-2
n/a
n/a