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Geotechnical Engineering Report
Proposed Huynh 3 Lot Short Plat
2007 Union Ave NE
Renton, Washington 98059
P/N 0423059076
July 14, 2017
prepared for:
Monsef Donogh Design Group
Attention: Paul Monsef
2806 NE Sunset Blvd, Suite F
Renton, Washington 98056
prepared by:
Migizi Group, Inc.
PO Box 44840
Tacoma, Washington 98448
(253) 537-9400
MGI Project P1003-T17
RECEIVED
12/27/2017
amorganroth
PLANNING DIVISION
i
TABLE OF CONTENTS
Page No.
1.0 SITE AND PROJECT DESCRIPTION............................................................................................... 1
2.0 EXPLORATORY METHODS ............................................................................................................. 2
2.1 Test Pit Procedures ................................................................................................................ 2
3.0 SITE CONDITIONS ............................................................................................................................ 3
3.1 Surface Conditions ................................................................................................................. 3
3.2 Soil Conditions ....................................................................................................................... 3
3.3 Groundwater Conditions ...................................................................................................... 4
3.4 Infiltration Conditions ........................................................................................................... 4
3.5 Seismic Conditions ................................................................................................................. 4
3.6 Liquefaction Potential ............................................................................................................ 5
4.0 CONCLUSIONS AND RECOMMENDATIONS ............................................................................ 5
4.1 Site Preparation ...................................................................................................................... 6
4.2 Spread Footings ...................................................................................................................... 8
4.3 Slab-On-Grade-Floors ............................................................................................................ 9
4.4 Asphalt Pavement .................................................................................................................. 9
4.5 Structural Fill ........................................................................................................................ 11
5.0 RECOMMENDED ADDITIONAL SERVICES .............................................................................. 12
6.0 CLOSURE ........................................................................................................................................... 12
List of Tables
Table 1. Approximate Locations and Depths of Explorations ............................................................................. 2
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
Log of Test Pits TP-1 through TP-3 ........................................................................................................... A-2…A-4
Page 1 of 12
MIGIZI GROUP, INC.
PO Box 44840 PHONE (253) 537-9400
Tacoma, Washington 98448 FAX (253) 537-9401
July 14, 2017
Monsef Donogh Design Group
2806 NE Sunset Blvd, Suite F
Renton, WA 98056
Attention: Paul Monsef
Subject: Geotechnical Engineering Report
Kathy Huynh 3-Lot SP
2007 Union Ave NE
Renton, WA 98059
P/N 0423059076
MGI Project P1003-T17
Dear Mr. Monsef:
Migizi Group, Inc. (MGI) is pleased to submit this report describing the results of our geotechnical
engineering evaluation of the proposed residential development in Renton, Washington.
This report has been prepared for the exclusive use of Monsef Donogh Design Group, 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 a rectangular-shaped, 0.74-acre residential parcel in Renton, Washington,
as shown on the enclosed Topographic and Location Map (Figure 1). The subject property is
situated along the west side of Union Ave NE, approximately 450 feet north of its intersection with
NE 19th St. The project area is elongated from east to west, spanning approximately 400 feet along
this orientation; extending upwards of 82 feet from north to south. The subject parcel has
previously been developed, with an existing single-family residence and detached garage originally
constructed in 1978 occupying the central portion of the site. Regions east and west of these
structures are occupied by yard space, with the driveway entering the site from the northeast.
Improvement plans involve the demolition of existing site features, and the eventual short-plat of
the subject property; resulting in three residential lots. Preliminary plans have each lot being
developed, and sharing a communal driveway which travels along the northern margin of the site.
Resulting lots will range from 9,676 to 12,300 sf, and will increase numerically from east to west.
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 2 of 12
2.0 EXPLORATORY METHODS
We explored surface and subsurface conditions at the project site on June 27, 2017. Our exploration
and evaluation program comprised the following elements:
• Surface reconnaissance of the site;
• Three test pit explorations (designated TP-1 through TP-3), advanced on June 27,
2017; 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 the test pits.
TABLE 1
APPROXIMATE LOCATIONS AND DEPTHS OF EXPLORATIONS
Exploration Functional Location
Termination
Depth
(feet)
TP-1
TP-2
TP-3
Southwest corner of the project area
Centrally, north side of project area
Southeast corner of the project area
10
8
5
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.
2.1 Test Pit Procedures
Our exploratory test pits were excavated with a rubber-tracked mini-excavator operated by an
excavation contractor under subcontract to MGI. An engineering geologist from our firm observed
the test pit excavations, collected soil samples, and logged the subsurface conditions.
The enclosed test pit logs indicate the vertical sequence of soils and materials encountered in our
test pits, based on our field classifications. Where a soil contact was observed to be gradational or
undulating, our logs indicate the average contact depth. We estimated the relative density and
consistency of the in-situ soils by means of the excavation characteristics and the stability of the test
pit sidewalls. Our logs also indicate the approximate depths of any sidewall caving or groundwater
seepage observed in the test pits. The soils were classified visually in general accordance with the
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 3 of 12
system described in Figure A-1, which includes a key to the exploration log. 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, and infiltration conditions.
3.1 Surface Conditions
As previously indicated, the project site consists of a rectangular-shaped, 0.74-acre residential parcel
in Renton, Washington. The subject property has previously been developed, with a single-family
residence and detached garage originally constructed in 1978 occupying the central portions of the
site. Regions east and west of these structures are occupied by yard space. A small garden area is
located within the north side of the back-yard area. Vegetation on site is limited to two larger fir
trees towards the western margin of the site, lawn grass, and scattered, ornamental trees/shrubs.
The project area is relatively level, with minimal grade change observed over its extent. The subject
property is situated within a densely populated residential area towards the northeast corner of the
city limits of Renton.
3.2 Soil Conditions
Our test pit explorations revealed relatively consistent subgrade conditions across the project area,
generally consisting of a surface mantle of sod/topsoil, underlain by native glacial till soils.
Renton, and the larger Puget Sound area in general, has been glaciated a number of times over the
last 2.4 million years. The most recent of these glacial events, the Vashon Stade of the Fraser
Glaciation, receded from this region approximately 13,500 years ago. The majority of near surface
soils encountered within the Renton area are either directly associated with, or have been physically
altered by the Vashon glacial event. Glacial till is typically described as being a compact, coherent
mixture of gravel, silt, clay and sand-sized clasts deposited along the base of glacial ice during a
period of localized advancement. This material is generally encountered in a compact relative
consistency given the fact that it was overridden by the ice mass shortly after deposition, and is
commonly underlain by advance outwash soils.
Underlying a surface mantle of sod and topsoil, we encountered native glacial till soils. The upper
± 3 feet of this soil group was highly weathered and encountered in a loose in situ condition.
Unweathered glacial till was comprised of dense, gravelly, silty sand and was continuous through
the termination depth of each of our subsurface explorations; a maximum depth of 10 feet below
grade. A slight variation to the above described soil sequence was observed in test pit exploration
TP-1, which was performed towards the west end of the project area. At this location, upwards of
3 feet of poorly to densely consolidated fill soils were encountered above native deposits. The
import of fill soils at this location was evidently required for the development of a level lot. Fill soils
were limited to the western margin of the project area, and will likely only be encountered in a
small portion of project excavations.
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 4 of 12
In the Geologic Map of the Renton Quadrangle, King County, Washington, as prepared by the
Department of the Interior United States Geological Survey (USGS) (1965), the project site is
mapped as containing Qvt, or Vashon-aged glacial till. The National Cooperative Soil Survey
(NCSS) for King County, classifies soils onsite as AgC – Alderwood gravelly sandy loam, 8 to
15 percent slopes. This soil series is comprised primarily of gravelly sandy loam, and reportedly
formed from glacial till deposits. Our subsurface explorations generally correspond with the
mappings of the site performed by the USGS and 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 slow seepage at a depth of approximately 9½ feet in the vicinity of test pit
exploration TP-1. This is likely indicative of seasonally high groundwater, given the fact that our
explorations were performed just outside of what is generally considered the rainy season, after
what has been one the wettest winters/springs recorded in Western Washington. Seasonally
perched groundwater, will also likely be encountered at shallow depths during extended periods of
wet weather due to the poor permeability of site soils.
3.4 Infiltration Conditions
As indicated in the soil conditions section of this report, the site is underlain by slowly permeable,
to relatively impermeable glacial till soils at shallow depths.
Given the geologic conditions present within the project area, we do not interpret full or limited
infiltration as being feasible for this project. Site produced stormwater should be managed through
dispersion, or other appropriate means.
3.5 Seismic Conditions
Based on our analysis of subsurface exploration logs and our review of published geologic maps,
we interpret the onsite soil conditions to generally correspond with site class C, as defined by
Table 30.2-1 in ASCE 7, per the 2015 International Building Code (IBC).
Using 2015 IBC information on the USGS Design Summary Report website, Risk Category I/II/III
seismic parameters for the site are as follows:
Ss = 1.412 g SMS = 1.412 g SDS = 0.941 g
S1 = 0.532 g SM1 = 0.692 g SD1 = 0.461 g
Using the 2015 IBC information, MCER Response Spectrum Graph on the USGS Design Summary
Report website, Risk Category I/II/III, Sa at a period of 0.2 seconds is 1.41 g and Sa at a period of
1.0 seconds is 0.69 g.
The Design Response Spectrum Graph from the same website, using the same IBC information and
Risk Category, Sa at a period of 0.2 seconds is 0.94 g and Sa at a period of 1.0 seconds is 0.46 g.
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 5 of 12
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 saturated, poorly consolidated granular soils were encountered
throughout the course of our test pit explorations. We interpret site soils as having a low potential
of liquefying during a large-scale seismic event.
4.0 CONCLUSIONS AND RECOMMENDATIONS
Improvement plans involve the demolition of existing site features, and the eventual short-plat of
the subject property; resulting in three residential lots. Preliminary plans have each lot being
developed, and sharing a communal driveway which travels along the northern margin of the site.
Resulting lots will range from 9,676 to 12,300 sf, and will increase numerically from east to west.
We offer these recommendations:
• Feasibility: Based on our field explorations, research and analyses, the proposed
structures appear feasible from a geotechnical standpoint.
• Foundation Options: Foundation elements for the proposed residences should be
constructed on medium dense or denser undisturbed native soils, or on structural
fill bearing pads extending down to these soils. We anticipate that adequate
bearing soils will be encountered within two to three feet of existing grade.
Recommendations for Spread Footings are provided in Section 4.2.
• Floor Options: Floor sections for the proposed residences should bear on medium
dense or denser native soils or on properly compacted structural fill extending down
to these soils. We anticipate that adequate bearing soils will be encountered within
two to three feet of existing grade. 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: Native, in-situ soil conditions are amenable to the use of soil-
supported pavements. 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
12 inches and replaced with a suitable structural fill material.
• Geologic Hazards: During our site reconnaissance, advancement of subsurface
explorations, and general evaluation of the proposed development, we did not
observe any erosional, landslide, seismic, settlement, or other forms of geologic
hazards within the subject property. Given this fact, we recommend that no buffers,
setbacks, or other forms of site restraints be implemented to address these potential
hazards.
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 6 of 12
The following sections of this report present our specific geotechnical conclusions and
recommendations concerning site preparation, spread footings, slab-on-grade floors, 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 3. 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 the organic horizon can reach thicknesses of up to 12 inches. Stripping is best performed
during a period of dry weather.
Site Excavations: Based on our explorations, we expect deeper site excavations will predominately
encounter densely consolidated glacial till soils. This soil group can be readily excavated utilizing
standard excavation equipment, though special teeth, or “rippers”, may need to be utilized in order
to rapidly excavate glacial till soils. Shallower excavations will encounter highly weathered, loosely
consolidated soils which can be readily excavated using standard excavation equipment.
Dewatering: We encountered slow seepage at a depth of ± 9½ feet in the vicinity of test pit
exploration TP-1. Given the relatively depth to groundwater, and the scope of this project, we do
not anticipate that groundwater will be encountered in most project excavations. However, if
groundwater is encountered, we anticipate that an internal system of ditches, sump holes, and
pumps will be adequate to temporarily dewater excavations.
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 7 of 12
Temporary Cut 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 should conform to Washington Industrial Safety and Health Act
(WISHA) regulations.
Subgrade Compaction: Exposed subgrades for the foundation of the proposed residence 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:
• Surficial Organic Soil and Organic-Rich Fill Soils: Where encountered, surficial organic
soils like duff, topsoil, root-rich soil, and organic-rich fill soils are not suitable for use
as structural fill under any circumstances, due to high organic content.
Consequently, this material can be used only for non-structural purposes, such as in
landscaping areas.
• Glacial Till: Underlying a surface mantle of sod and topsoil, native glacial till soils
were encountered; generally consisting of dense, gravelly silty sand. These soils are
moderately moisture sensitive and will be difficult, if not impossible, to reuse during
wet weather conditions. If reuse is planned, care should be taken while stockpiling
in order to avoid saturation/over-saturation of the material, and moisture
conditioning should be expected.
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.
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.
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 8 of 12
4.2 Spread Footings
In our opinion, conventional spread footings will provide adequate support for the proposed
residences 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: Footings should bear on medium dense or denser, undisturbed native soils
which have been stripped of surficial organic soils and vigorously surface compacted, or on
properly compacted structural fill bearing pads which extend down to soils described above. We
anticipate that adequate bearing subgrades will be encountered within 2 to 3 feet of existing grade,
within unweathered glacial till soils.
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 moderately consolidated
recessional outwash soils can be designed for a maximum allowable soil bearing pressure of
2,000 psf. A one-third increase in allowable 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.
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 9 of 12
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, soil-supported slab-on-grade floors can be used in the proposed residences if the
subgrades are properly prepared. Floor sections for the proposed structures should bear on
medium dense or denser native soils or on properly compacted structural fill which extends down
to soils described above. We anticipate that adequate bearing soils will be encountered within 2 to
3 feet of existing grade. We offer the following comments and recommendations concerning slab-
on-grade floors.
Floor Subbase: Surface compaction of all slab subgrades is recommended. If a subbase is required,
it 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.
Vertical Deflections: Due to elastic compression of subgrades, soil-supported slab-on-grade floors
can deflect downwards when vertical loads are applied. In our opinion, a subgrade reaction
modulus of 250 pounds per cubic inch can be used to estimate such deflections.
4.4 Asphalt Pavement
Since asphalt pavements will also be used for the proposed communal driveway system, we offer
the following comments and recommendations for pavement design and construction.
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 maximum depth of 12 inches 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
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 10 of 12
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) 6 inches 12 inches
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 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.
Monsef Donogh Design Group – Kathy Huynh 3-Lot SP, 2007 Union Ave NE, Renton, WA July 14, 2017
Geotechnical Engineering Report P1003-T17
Migizi Group, Inc. Page 11 of 12
4.5 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. 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
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.
APPROXIMATE SITE
LOCATION
P.O. Box 44840
Tacoma, WA 98448
Location Job Number Figure
DateTitle
2007 Union Ave NE
Renton, WA
P/N 0423059076
Topographic and Location Map
1
06/20/17
P1003-T17
APPENDIX A
SOIL CLASSIFICATION CHART AND
KEY TO TEST DATA
LOG OF TEST PITS
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, POOORLY 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.
GB
S-1
GB
S-2
SM
SP-
SM
SM
SM
SM
0.6
2.5
3.0
4.5
10.0
(SM) Gray/brown silty sand with gravel (loose, damp) (Fill)
(SP-SM) Gray/brown fine to medium sand with silt and gravel (dense, moist) (Fill)
(SM) Dark brown silty sand with some gravel and abundant organics (loose, moist) (Old Topsoil Horizon)
(SM) Orange/brown fine silty sand with some gravel (medium dense, moist) (Weathered Glacial Till)
(SM) Gray silty sand with gravel (dense, moist) (Unweathered Glacial Till)
No caving observed
Slow groundwater seepage observed at 9.5 feet
The depths on the test pit logs are based on an average of measurements across the test pit and should be
considered accurate to 0.5 foot.
Bottom of test pit at 10.0 feet.
NOTES
LOGGED BY ZLL
EXCAVATION METHOD Rubber Tracked Mini Excavator
EXCAVATION CONTRACTOR Paulman GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 6/27/17 COMPLETED 6/27/17
AT TIME OF EXCAVATION 9.50 ft Slow seepage
AT END OF EXCAVATION ---
AFTER EXCAVATION ---
TEST PIT SIZEGROUND ELEVATION
SAMPLE TYPENUMBERDEPTH(ft)0.0
2.5
5.0
7.5
10.0
PAGE 1 OF 1
Figure A-2
TEST PIT NUMBER TP-1
CLIENT Monsef Donogh Design Group
PROJECT NUMBER P1003-T17
PROJECT NAME Proposed Huynh 3 Lot Short Plat Geotech
PROJECT LOCATION 2007 Union Ave NE, Renton, WA
COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 7/7/17 15:42 - C:\USERS\JESSICA\DESKTOP\TEST PITS AND BORINGS - GINT\P1003-T17\P1003-T17 TEST PITS.GPJMigizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
Fax: 253-537-9401
U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
GB
S-1
GB
S-2
SM
SM
SM
0.8
3.0
8.0
(SM) Gray/brown silty sand with gravel (loose, damp) (Fill)
(SM) Orange/brown fine silty sand with some gravel (loose, moist) (Weathered Glacial Till)
(SM) Gray silty sand with gravel (dense, moist) (Unweathered Glacial Till)
No caving observed
No groundwater seepage observed
The depths on the test pit logs are based on an average of measurements across the test pit and should be
considered accurate to 0.5 foot.
Bottom of test pit at 8.0 feet.
NOTES
LOGGED BY ZLL
EXCAVATION METHOD Rubber Tracked Mini Excavator
EXCAVATION CONTRACTOR Paulman GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 6/27/17 COMPLETED 6/27/17
AT TIME OF EXCAVATION ---
AT END OF EXCAVATION ---
AFTER EXCAVATION ---
TEST PIT SIZEGROUND ELEVATION
SAMPLE TYPENUMBERDEPTH(ft)0.0
2.5
5.0
7.5
PAGE 1 OF 1
Figure A-3
TEST PIT NUMBER TP-2
CLIENT Monsef Donogh Design Group
PROJECT NUMBER P1003-T17
PROJECT NAME Proposed Huynh 3 Lot Short Plat Geotech
PROJECT LOCATION 2007 Union Ave NE, Renton, WA
COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 7/7/17 15:42 - C:\USERS\JESSICA\DESKTOP\TEST PITS AND BORINGS - GINT\P1003-T17\P1003-T17 TEST PITS.GPJMigizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
Fax: 253-537-9401
U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION
GB
S-1
SM
SM
SM
1.0
3.0
5.0
(SM) Gray/brown silty sand with gravel (loose, damp) (Fill)
(SM) Orange/brown fine silty sand with some gravel (loose, moist) (Weathered Glacial Till)
(SM) Gray silty sand with gravel (dense, moist) (Unweathered Glacial Till)
No caving observed
No groundwater seepage observed
The depths on the test pit logs are based on an average of measurements across the test pit and should be
considered accurate to 0.5 foot.
Bottom of test pit at 5.0 feet.
NOTES
LOGGED BY ZLL
EXCAVATION METHOD Rubber Tracked Mini Excavator
EXCAVATION CONTRACTOR Paulman GROUND WATER LEVELS:
CHECKED BY JEB
DATE STARTED 6/27/17 COMPLETED 6/27/17
AT TIME OF EXCAVATION ---
AT END OF EXCAVATION ---
AFTER EXCAVATION ---
TEST PIT SIZEGROUND ELEVATION
SAMPLE TYPENUMBERDEPTH(ft)0.0
2.5
5.0
PAGE 1 OF 1
Figure A-4
TEST PIT NUMBER TP-3
CLIENT Monsef Donogh Design Group
PROJECT NUMBER P1003-T17
PROJECT NAME Proposed Huynh 3 Lot Short Plat Geotech
PROJECT LOCATION 2007 Union Ave NE, Renton, WA
COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 7/7/17 15:42 - C:\USERS\JESSICA\DESKTOP\TEST PITS AND BORINGS - GINT\P1003-T17\P1003-T17 TEST PITS.GPJMigizi Group, Inc.
PO Box 44840
Tacoma, WA 98448
Telephone: 253-537-9400
Fax: 253-537-9401
U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION