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ENGINEERING AND SURVEYING
REPORT ON GEOTECHNICAL OBSERVATIONS
Bicycle Apartments, LLC
Proposed Residential Housing Development 118 North 50th Avenue
Yakima, Washington 98907
Yakima County Tax Parcel Id: 181321-41425
April 11, 2017
PLSA Project No. 17087
Prepared for:
Bicycle Apartments, LLC c/o Next Step Housing
P.O. Box 784
Yakima, WA 98907
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Table of Contents 1 Introduction ............................................................................................................................. 1
2 Land Use and Surface Conditions ........................................................................................... 1
3 Seismic Considerations............................................................................................................ 1
4 Liquifaction Potential .............................................................................................................. 2
5 Sub-Surface Conditions ........................................................................................................... 2
6 Soil Bearing Recommendations .............................................................................................. 3
7 Lateral Earth Pressure .............................................................................................................. 3
8 Structural Fill ........................................................................................................................... 4
9 Stormwater Disposal (Soil Infiltration Rates) ......................................................................... 4
10 Paving Recommendations .................................................................................................... 5
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1 INTRODUCTION
Bicycle Apartments, LLC, retained PLSA Engineering and Surveying to perform a geotechnical
investigation on an approximate 3 acre property, located approximately 1 block south of
Summitview Avenue, on the west side of 50th Avenue in Yakima Washington. See Appendix “A”
for vicinity map.
This report summarizes the results of our geotechnical investigation and offers our
recommendations for soil bearing values and site preparation for mobilizing soil support for a
future paved parking facility. The investigation consisted of visual inspection of the area, drawing
upon extensive local knowledge of nearby soil conditions, and examination and logging of 5 test
pits excavated using a John Deere 410L tractor mounted backhoe. See Appendix “B” Test Pit
Location Map. A geotechnical engineer from PLSA, experienced with local soil conditions, logged
the excavations and observed and field classified the soils found.
Included in this report are the following:
• Seismic zone information.
• Liquefaction Potential.
• Excavation logs and field classifications of the soils encountered in the 5 test pits.
• Estimated frost penetration.
• Structural fill recommendations.
• Recommended minimum footing depth and width.
• Recommended footing trench preparation.
• Soil bearing recommendations.
• Lateral Earth Pressure
• Stormwater Recommendations
• Slab on grade support recommendations.
• Parking lot site preparation and paving recommendations.
2 LAND USE AND SURFACE CONDITIONS
The subject property is vacant and located on a bench approximately 6 feet above 50th Avenue and
the adjacent property to the south. Elevations on the north and west boundaries are nearly level
with the adjacent properties along those boundaries. The site generally slopes to the South at
approximately 5 percent. The surface is well vegetated with healthy field grass. Several large trees
populate the northwest corner. Surrounding property use consists of a mix of residences and
commercial and professional businesses.
3 SEISMIC CONSIDERATIONS
Based on Table 20.3-1 found in ASCE-7, Chapter 20, and the firm silt observed during the field
investigation, the site is classified as Soil Class D. This classification is also in general agreement
with the Site Class Map of Yakima County, Washington published by the Washington State
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Department of Natural Resources. Site specific design values, using the Class D designation, are
provided below in Table 1.
Table 1: USGS Seismic Design Parameters
0.2 Second 1.0 Second
Maximum Considered Earthquake (MCE) Spectral
Acceleration
Ss=0.525 S1=0.215
Site Coefficient Fa=1.380 Fv=1.970
MCE Adjusted for Site Class effects SMS=0.724 SM1=0.424
Design Spectral Acceleration SDS=0.483 SD1=0.283
4 LIQUEFACTION POTENTIAL
Liquefaction is a phenomenon caused by a rapid increase in pore water pressure, in loose soils,
that reduces the effective stress between soil particles to near zero. This rapid increase in pore
water pressure can cause a loss of soil shear strength. Groundwater was not observed during the
field investigation and is known to be at depths of more than 50 feet below the ground surface
(bgs). Absence of groundwater eliminates the potential of liquefaction. In agreement with the field
observations, the Washington State Department of Natural Resources Liquefaction Susceptibility
maps show the susceptibility of this location to be low.
5 SUB-SURFACE CONDITIONS
Observations in all 5 test pits were similar. Fill consisting of 1 to 3 feet of sandy silt was observed
overlying a deep stratum of silt that increased in cemented qualities with depth. Hard pan can be
expected at a depth of 10 feet bgs. See test pit logs found in Appendix “C”.
USDA Soil Conservation Service classifies the native topsoil as "Esquatzel Silt Loam".
Permeability reported as moderately high, and therefore suitable for on-site stormwater disposal.
Before designing any on-site stormwater disposal system, an investigation of current local
stormwater disposal requirements is recommended.
Frost action is usually severe in the area due to the water holding capacity of the silt soil. Frost
penetration for the project location is estimated at 30 inches. Frost damage may be minimized by
placing footings a minimum of 30 inches below finished grade and by directing drainage away
from the buildings.
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6 SOIL BEARING RECOMMENDATIONS
PLSA understands that development of the property will include the construction of 5 apartment
buildings with up to 3 stories and 80 apartment units. The development will also include all
necessary utilities, access drives, parking lots, and pedestrian sidewalks. A minimum footing depth
of 3 feet below finished grade is recommended, for mobilization of soil strength and frost
protection. Footing depth is measure to the bottom of the gravel capillary barrier as specified
below. The recommended minimum footing width is two feet.
Recommended footing trench preparation is as follows: Excavated footing trenches two feet
wider than the footing width and 12 inches deeper than the desired bottom of concrete footing
depth. Proof roll the exposed trench bottom to 95 percent of maximum density as determined by
ASTM D-1557. Place a minimum of 12 inches of compacted, cohesionless, free-draining, gravel,
such as 1¼ inch minus crushed surfacing base course, in the prepared footing trench, up to desired
bottom of concrete footing grade. Compact the crushed rock in lifts to 95 percent of maximum
density as determined by ASTM D-1557 to produce a firm, stable, and unyielding surface. Using
a minimum footing width and the footing trench preparation recommended above, satisfactory soil
support for loadings up to 2,000 pounds per square foot (psf) should be achieved. If a greater soil
bearing value is required contact this office for additional recommendations.
Slabs on grade may be placed over silt surface soil. Remove all vegetation and other organic
material from over areas planned to support slabs. Compact the exposed surface, for depth of 8
inches, to 95 percent of maximum compaction as determined by ASTM D-1557. If optimum
moisture content for compaction is exceeded, dry the soil by excavation, aeration, or replacement.
Place a 6-inch minimum thickness, capillary barrier, consisting of compact, granular, free-draining
material such as 5/8 inch minus crushed rock meeting APWA standard specifications for top
course. Compact the granular material in a minimum of two layers to 95 percent of maximum
density as determined by ASTM D-1557. Using this preparation, a subgrade reaction value, Ks,
of 200 pounds per cubic inches (pic) should be achieved.
All roof and surface drainage is recommended to be directed away from the footings and exterior
slabs. Buildings should be elevated or placed on structural fill as necessary to provide slope to
insure adequate drainage.
7 LATERAL EARTH PRESSURE
Magnitude of lateral earth pressure varies with the height of the supported face, soil internal
friction, backfill soil density, presence or absence of water, and amount of surcharge, if any. PLSA
recommends selecting 110 pounds per cubic foot (pcf) as an appropriate unit weight of compacted
native soil backfill. Use of other soil types for backfill will require using a unit weight appropriate
for the type of soil selected.
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Coefficients of lateral pressure and unsaturated equivalent fluid weight for the native silt is as
follows:
Equivalent Fluid Wt. (pcf)
Sand & Gravel
Active Ka 0.33 40
At Rest Ko 0.50 55
Passive Kp 3.00 330
8 STRUCTURAL FILL
All areas to receive structural fill are recommended to be stripped of all paving, vegetation, organic
material, and trash. Proof rolled the exposed surface to 95 percent of maximum density as
determined by ASTM D-1557 for a depth of 6 inches before placing fill. The soil should be near
optimum moisture content for compaction. Add water or dry the soil by processing as necessary
to achieve moisture content suitable for compaction. If the fill subgrade soils are persistently too
wet to achieve specified compaction, contact this office for additional fill subgrade preparation
recommendations.
Imported soil used for structural fill is recommended to be cohesionless, free draining, non-plastic
material with a maximum particle size of two inches, or other material as approved by a
geotechnical engineer from this office.
All structural fill should be placed and compacted in layers not exceeding 6 inches in thickness.
Water should be added as needed to achieve satisfactory moisture content for compaction. Soils
too wet to be adequately compacted should be dried to a suitable moisture content before
incorporation into structural fill. Recommended compaction for structural fill is 95 percent of
maximum density as determined by ASTM D-1557. It is further recommended that all soil
compaction as recommended herein be monitored using a nuclear density gauge and documented.
Structural fill should not be placed over debris which may be poorly consolidated or contain
organic material or metal that may decompose and settle with time. All such unsuitable materials
should be removed and replaced with additional structural fill as described above.
Excavations resulting from removal of underground structures such as septic tanks, or petroleum
tanks are recommended to be backfilled using procedures described for structural fill.
Structural fill placed as described above is expected to provide bearing support equivalent to that
for recommended preparation of footing trenches in the native soil supporting the fill. Soil bearing
support for slabs on grade on structural fill placed as recommended herein is also expected to be
equivalent to that recommended for the native soil prepared as recommended herein.
9 STORMWATER DISPOSAL (SOIL INFILTRATION RATES)
The soil observed for several feet below the ground surface contains a fine silt and/or significant
silt component. The USDA Web Soil Survey reports that these soils are classified in the
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Hydrologic Soils Group B with a moderately high rate of infiltration. The minimum report cation-
exchange capacity (CEC), for the native soil, is 7.5 milliequivalents per 100 grams of dry soil,
exceeding the minimum requirement of 5 milliequivalents. The site is suitable for stormwater
disposal by infiltration. Based on experience with these soils, a long-term infiltration rate of 0.50
inches per hour can be expected for the native undisturbed silt. All construction traffic is
recommended to be prohibited in areas that are proposed to be used for stormwater infiltration.
Even minimal incidental compaction can reduce infiltration performance significantly.
All roof and surface drainage is recommended to be directed away from the footings. Buildings
should be elevated or placed on structural fill as necessary to provide slope to insure adequate
drainage.
10 PAVING RECOMMENDATION
All areas to be paved should be cleared of all grass, roots, trash, metal and organic materials down
to full depth below the paving mat. The exposed soil surface should then be proof rolled to a 6-
inch depth, to 90 percent of the maximum theoretical density as determined by ASTM D-1557,
using a mechanical vibratory compactor.
The following specification is our recommendation for paving and subgrade: Asphaltic Concrete
Paving, mix design and placement, shall conform to Washington State Department of
Transportation (WSDOT) Standard Specifications 2016, Division 5, Class HMA ½. Areas subject
to truck traffic shall be a minimum of 3 inches, compacted thickness, of asphaltic concrete placed
over a minimum of 9 inches of free-draining, crushed surfacing conforming to the particle size
distribution for Base Coarse found in section 9-03.9(3) of the WSDOT Standard Specifications.
Base Coarse gravel shall be compacted in lifts to 90 percent of the maximum theoretical density
as determined by ASTM D-1557, using a mechanical vibratory compactor.
Asphaltic concrete paving placed on parking lot areas used exclusively by automobiles may be
reduced to 2 inches compacted thickness.
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APPENDIX A:
Vicinity Map
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GarlandS
Text Box
FIGURE 1 VICINITY MAP 118 North 50th Avenue, Yakima, WA PREPARED FOR Bicycle Apartments, LLC
GarlandS
Text Box
PLSA ENGINEERING-SURVEYING-PLANNING 521 NORTH 20TH AVENUE, YAKIMA, WA (509) 575-6990
GarlandS
Text Box
Date: 04-11-2017
GarlandS
Text Box
PLSA Project No. 17087
GarlandS
Text Box
Yakima County Parcel 181321-41425
GarlandS
Callout
SITE: 118 North 50th Avenue Yakima, WA
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APPENDIX B:
Test Pit Location Map
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GarlandS
Text Box
TEST PIT LOCATION MAP 118 NORTH 50TH AVENUE, YAKIMA WA PREPARED FOR BICYCLE APARTMENTS, LLC
GarlandS
Text Box
TP-? Approximate Test Pit Location
GarlandS
Text Box
PLSA ENGINEERING-SURVEYING-PLANNING 521 North 20th AVENUE, YAKIMA, WA (509) 575-6990
GarlandS
Text Box
Date: 04-11-2017
GarlandS
Text Box
PLSA Project No. 17087
GarlandS
Text Box
Yakima County Parcel 181321-41425
Garland
Text Box
North 50th Avenue
Garland
Text Box
Summitview Avenue
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APPENDIX C:
Test Pit Logs
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PLSA ENGINEERING & SURVEYING
By: SDG Date: 3/6/2017
Elevation: N/A
Dep
th (
ft)
Mo
istu
re
Co
nte
nt
%
Un
it
Wei
gh
t
Sa
mp
le
UC
S
Sy
mb
ol
1 ML
2
3
4
5
ML
6
7
8
9
10
11
12
13
14
15
16
RemarksDescription
Surface Conditions: Grass
Location: NE 1/4 of Site
EXCAVATION LOG NO.: 1
509-575-6990
1120 WEST LINCOLN AVENUE
YAKIMA, WA 98902
Project No.: 17087
ML Silt
Sandy Silt
Thin Ash Layer
Silt
Firm - Fill
Med Brown
Moist
Firm
Dark Brown
Firm
Light Brown
Dry
Very Firm
DryML Partially Cemented Silt
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PLSA ENGINEERING & SURVEYING
By: SDG Date: 3/6/2017
Elevation: N/A
Dep
th (
ft)
Mo
istu
re
Co
nte
nt
%
Un
it
Wei
gh
t
Sa
mp
le
UC
S
Sy
mb
ol
1 ML
2
3
4
5
ML
6
7
8
9
10
11
12
13
14
15
16
ML Partially Cemented Silt Very Firm
Dry
Firm
Silt Light Brown
Dry
Firm - Fill
Sandy Silt Med Brown
Moist
Location: NW 1/4 of Site
Surface Conditions: Grass
Description Remarks
1120 WEST LINCOLN AVENUE
YAKIMA, WA 98902
509-575-6990
EXCAVATION LOG NO.: 2
Project No.: 17087
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PLSA ENGINEERING & SURVEYING
By: SDG Date: 3/6/2017
Elevation: N/A
Dep
th (
ft)
Mo
istu
re
Co
nte
nt
%
Un
it
Wei
gh
t
Sa
mp
le
UC
S
Sy
mb
ol
1
ML
2
3
4
5
ML
6
7
8
9
10
11
12
13
14
15
16
Firm
Cemented Silt Light Brown
Dry
Thin Ash Layer
Moist
Firm - Fill
Sandy Silt Med Brown
Location: SW 1/4 of Site
Surface Conditions: Grass
Description Remarks
1120 WEST LINCOLN AVENUE
YAKIMA, WA 98902
509-575-6990
EXCAVATION LOG NO.: 3
Project No.: 17087
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PLSA ENGINEERING & SURVEYING
By: SDG Date: 3/6/2017
Elevation: N/A
Dep
th (
ft)
Mo
istu
re
Co
nte
nt
%
Un
it
Wei
gh
t
Sa
mp
le
UC
S
Sy
mb
ol
1 ML
2
3
4
ML
5
6
7 ML
8
9
10
11
12
13
14
15
16
Cemented Silt Very Firm
Dry
Dry
Firm
Partially Cemented Silt Light Brown
Firm - Fill
Sandy Silt Med Brown
Moist
Location: South Center Area of Site
Surface Conditions: Grass
Description Remarks
1120 WEST LINCOLN AVENUE
YAKIMA, WA 98902
509-575-6990
EXCAVATION LOG NO.: 4
Project No.: 17087
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PLSA ENGINEERING & SURVEYING
By: SDG Date: 3/6/2017
Elevation: N/A
Dep
th (
ft)
Mo
istu
re
Co
nte
nt
%
Un
it
Wei
gh
t
Sa
mp
le
UC
S
Sy
mb
ol
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
ML Cemented Silt
ML Silt
ML Sandy Silt
Very Firm
Light Brown
Dry
Firm
Med Brown-Moist
Firm - Fill
Med Brown-Moist
Thin Ash Layer
Location: East 1/3 of Site
Surface Conditions: Grass
Description Remarks
1120 WEST LINCOLN AVENUE
YAKIMA, WA 98902
509-575-6990
EXCAVATION LOG NO.: 5
Project No.: 17087