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GEOTECHNICAL ENGINEERING REPORT
PREPARED BY:
THE RILEY GROUP, INC.
17522 BOTHELL WAY NORTHEAST
BOTHELL, WASHINGTON 98011
PREPARED FOR:
WESTON HEIGHTS, LLC
15 LAKE BELLEVUE DRIVE, SUITE 102
BELLEVUE, WASHINGTON 98005
RGI PROJECT NO. 2016-009
WESTON NORTH
702 NILE AVENUE NORTHEAST
RENTON, WASHINGTON
JANUARY 29, 2016
Geotechnical Engineering Report i January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
TABLE OF CONTENTS
1.0 INTRODUCTION ............................................................................................................................... 1
2.0 PROJECT DESCRIPTION ............................................................................................................... 1
3.0 FIELD EXPLORATION AND LABORATORY TESTING .......................................................... 1
3.1 FIELD EXPLORATION ................................................................................................................................... 1
3.2 LABORATORY TESTING ................................................................................................................................ 2
4.0 SITE CONDITIONS ........................................................................................................................... 2
4.1 SURFACE .................................................................................................................................................. 2
4.2 GEOLOGY ................................................................................................................................................. 2
4.3 SOILS ....................................................................................................................................................... 3
4.4 GROUNDWATER ........................................................................................................................................ 3
4.5 SEISMIC CONSIDERATIONS ........................................................................................................................... 3
4.6 GEOLOGIC HAZARD AREAS .......................................................................................................................... 4
5.0 DISCUSSION AND RECOMMENDATIONS ................................................................................. 4
5.1 GEOTECHNICAL CONSIDERATIONS ................................................................................................................. 4
5.2 EARTHWORK ............................................................................................................................................. 4
5.2.1 Erosion and Sediment Control ..................................................................................................... 4
5.2.2 Stripping ....................................................................................................................................... 5
5.2.3 Excavations................................................................................................................................... 6
5.2.4 Site Preparation ........................................................................................................................... 6
5.2.5 Structural Fill ................................................................................................................................ 7
5.2.6 Cut and Fill Slopes ........................................................................................................................ 8
5.2.7 Wet Weather Construction Considerations ................................................................................. 8
5.3 FOUNDATIONS .......................................................................................................................................... 9
5.4 RETAINING WALLS ................................................................................................................................... 10
5.5 SLAB-ON-GRADE CONSTRUCTION ............................................................................................................... 10
5.6 DRAINAGE .............................................................................................................................................. 11
5.6.1 Surface ....................................................................................................................................... 11
5.6.2 Subsurface .................................................................................................................................. 11
5.6.3 Infiltration .................................................................................................................................. 11
5.7 UTILITIES ................................................................................................................................................ 11
5.8 PAVEMENTS ............................................................................................................................................ 11
6.0 ADDITIONAL SERVICES .............................................................................................................. 12
7.0 LIMITATIONS ................................................................................................................................. 12
LIST OF FIGURES AND APPENDICES
Figure 1 ..................................................................................................................... Site Vicinity Map
Figure 2 ............................................................................................... Geotechnical Exploration Plan
Figure 3 ...................................................................................Typical Retaining Wall Drainage Detail
Figure 4 ....................................................................................................Typical Footing Drain Detail
Appendix A .......................................................................... Field Exploration and Laboratory Testing
Geotechnical Engineering Report ii January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
Executive Summary
This Executive Summary should be used in conjunction with the entire Geotechnical
Engineering Report (GER) for design and/or construction purposes. It should be
recognized that specific details were not included or fully developed in this section, and
the GER must be read in its entirety for a comprehensive understanding of the items
contained herein. Section 7.0 should be read for an understanding of limitations.
RGI’s geotechnical scope of work included the advancement of 3 hand augers to a
maximum depth of 3.5 feet below existing site grades.
Based on the information obtained from our subsurface exploration, the site is suitable
for development of the proposed project. The following geotechnical considerations were
identified:
Soil Conditions: The soils encountered during field exploration includes soft to medium
stiff silt with some sand and medium dense silty sand with some gravel .
Groundwater: Light groundwater seepage was encountered between depths of 8 to 18
inches bgs during our subsurface exploration.
Foundations: Foundations for the proposed building may be supported on conventional
spread footings bearing on medium dense to dense native soil or structural fill.
Slab-on-grade: Slab-on-grade floors and slabs for the proposed building can be supported
on medium dense to dense native soil or structural fill.
Pavements: The following pavement sections are recommended:
For heavy truck traffic areas: 3 inches of Hot Mix Asphalt (HMA) over 6 inches of
crushed rock base (CRB)
For general parking areas: 2 inches of HMA over 4 inches of CRB
Geotechnical Engineering Report 1 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
1.0 Introduction
This Geotechnical Engineering Report (GER) presents the results of the geotechnical
engineering services provided for the Weston North short plat in Renton, Washington.
The purpose of this evaluation is to assess subsurface conditions and provide
geotechnical recommendations for the construction of single family residences. Our
scope of services included field explorations, laboratory testing, engineering analyses, and
preparation of this GER.
The recommendations in the following sections of this GER are based upon our current
understanding of the proposed site development as outlined below. If actual features
vary or changes are made, RGI should review them in order to modify our
recommendations as required. In addition, RGI requests to review the site grading plan,
final design drawings and specifications when available to verify that our project
understanding is correct and that our recommendations have been properly interpreted
and incorporated into the project design and construction.
2.0 Project description
The project site is located at 702 Nile Avenue Northeast in Renton, Washington. The
approximate location of the site is shown on Figure 1. The site is currently occupied by a
single family residence with a shop to the west and a grass field to the east of the
residence.
RGI understands that the parcel will be subdivided into six lots with construction of five
new single family residences. The existing residence and shop will remain on Lot 1. Our
understanding of the project is based on conversations with the client, and a site plan
that was forwarded to us by SDA dated October 24, 2015.
At the time of preparing this GER, building plans were not available for our review. Based
on our experience with similar construction, RGI anticipates that the proposed building
will be supported on perimeter walls with bearing loads of two to four kips per linear
foot, and a series of columns with a maximum load up to 20 kips. Slab-on-grade floor
loading of 250 pounds per square foot (psf) are expected.
3.0 Field Exploration and Laboratory Testing
3.1 FIELD EXPLORATION
On January 22, 2016, RGI excavated three hand augers. The approximate exploration
locations are shown on Figure 2.
Field logs of each exploration were prepared by the geologist that completed the
excavation. These logs included visual classifications of the materials encountered during
excavation. The hand augers logs included in Appendix A represent an interpretation of
Geotechnical Engineering Report 2 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
the field logs and include modifications based on laboratory observation and analysis of
the samples.
3.2 LABORATORY TESTING
During the field exploration, a representative portion of each recovered sample was
sealed in containers and transported to our laboratory for further visual and laboratory
examination. Selected samples retrieved from the hand augers were tested for moisture
content and grain size analysis, to aid in soil classification and provide input for the
recommendations provided in this GER. The results and descriptions of the laboratory
tests are enclosed in Appendix A.
4.0 Site Conditions
4.1 SURFACE
The subject site is a rectangular-shaped parcel of land approximately 2.3 acres in size. The
site is bound to the north by Northeast 7th Place, to the east by residential property and
a private road, to the south by a wetland and residential properties, and to the west by
Nile Avenue Northeast.
The existing site houses a shop and a single family residence that are located within the
western section of the site. A handful of trees are located along the western portion of
the south property line with a cluster of 20 foot tall bamboo stalks to the northeast of the
house. The remaining area (central to eastern portion of the site) is occupied by a large
grassy field, where the proposed new single family residences would be constructed. The
site is relatively flat with an overall elevation difference of approximately 6 feet,
increasing in elevation towards the east.
4.2 GEOLOGY
Review of the Geologic Map of the Renton Quadrangle King County, Washington, by D.R.
Mullineaux, (1965) indicates that the soil in the project vicinity is mapped as Ground
moraine deposits (Qgt), which is mostly thin ablation till over lodgment till, deposited by
Puget glacial lobe. Lodgment till generally compact, coherent, unsorted mixture of sand,
silt, clay and gravel: commonly termed hardpan. Ablation till similar, but much less
compact and coherent. Highly variable in thickness and in relative proportion of lodgment
to ablation till; lodgment till generally 5 to 30 feet thick, ablation till 2 to 10 feet. North of
Cedar River, till is mostly sand, is relatively friable and locally less than 5 feet thick.
Between Renton and Lake Youngs, lodgment till locally is thin, but ablation till is relatively
thick and grades to stratified drift. Moderately drumlinized, forms undulating, locally
irregular surface characterized by southeast-ward-trending hills and swales, commonly
overlain by thin sand, clay or peat. Surface drainage is locally poor. Lodgment till is
nearly impermeable and relatively difficult to excavate, but relatively stable in cut slopes.
These descriptions are generally similar to the findings in our field explorations.
Geotechnical Engineering Report 3 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
4.3 SOILS
The soils encountered during field exploration include silt with some sand to silty sand
with some gravel. Hand auger locations HA-2 and HA-3 encountered dense to very dense
soils that contained large gravels and cobbles that prevented further advancement in
depth.
More detailed descriptions of the subsurface conditions encountered are presented in
the hand auger logs included in Appendix A. Sieve analysis was performed on two
selected soil samples. Grain size distribution curves are included in Appendix A.
4.4 GROUNDWATER
Light groundwater seepage was encountered between 8 to 18 inches bgs during our
subsurface exploration. The groundwater appears to be perched over the top of a
medium stiff SILT layer. Surface water was also observed in the grassy field during the
exploration.
It should be recognized that fluctuations of the groundwater table will occur due to
seasonal variations in the amount of rainfall, runoff, and other factors not evident at the
time the explorations were performed. In addition, perched water can develop within
seams and layers contained in fill soils or higher permeability soils overlying less
permeable soils following periods of heavy or prolonged precipitation. Therefore,
groundwater levels during construction or at other times in the future may be higher or
lower than the levels indicated on the logs. Groundwater level fluctuations should be
considered when developing the design and construction plans for the project.
4.5 SEISMIC CONSIDERATIONS
Based on the 2012 International Building Code (IBC), RGI recommends the follow seismic
parameters for design.
Table 1 2012 IBC
Parameter Value
Site Soil Class1 C2
Site Latitude 47.494016o N
Site Longitude 122.141161o W
Short Period Spectral Response Acceleration, SS (g) 1.387
1-Second Period Spectral Response Acceleration, S1 (g) 0.521
Adjusted Short Period Spectral Response Acceleration, SMS (g) 1.387
Adjusted 1-Second Period Spectral Response Acceleration, SM1 (g) 0.677
1. Note: In general accordance with Chapter 20 of ASCE 7. The Site Class is based on the average characteristics of the upper 100 feet
of the subsurface profile.
Geotechnical Engineering Report 4 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
2. Note: The 2012 IBC and ASCE 7 require a site soil profile determination extending to a depth of 100 feet for seismic site
classification. The current scope of our services does not include the required 100 foot soil profile determination. Hand augers
extended to a maximum depth of 3.5 feet, and this seismic site class definition considers that very dense soil continues below the
maximum depth of the subsurface exploration. Additional exploration to deeper depths would be required to confirm the conditions
below the current depth of exploration.
Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength
due to an increase in water pressure induced by vibrations from a seismic event.
Liquefaction mainly affects geologically recent deposits of fine-grained sands that are
below the groundwater table. Soils of this nature derive their strength from intergranular
friction. The generated water pressure or pore pressure essentially separates the soil
grains and eliminates this intergranular friction, thus reducing or eliminating the soil’s
strength.
RGI reviewed the results of the field and laboratory testing and assessed the potential for
liquefaction of the site’s soil during an earthquake. Since the site is underlain by glacial
till, RGI considers that the possibility of liquefaction during an earthquake is minimal.
4.6 GEOLOGIC HAZARD AREAS
Regulated geologically hazardous areas include erosion, landslide, earthquake, or other
geological hazards. Based on the definitions in the Renton Municipal Code, the site does
not contain geologically hazardous areas. There are not mapped coal mine hazards, steep
slopes or landslide hazard on the site or in the near vicinity of the site. A wetland is
mapped on the parcel to the south of the site and appears to extend slightly into the site.
5.0 Discussion and Recommendations
5.1 GEOTECHNICAL CONSIDERATIONS
Based on our study, the site is suitable for the proposed construction from a geotechnical
standpoint. Foundations for the proposed building can be supported on conventional
spread footings bearing on medium dense to dense native soil or structural fill. Slab-on-
grade and pavements can be similarly supported.
Detailed recommendations regarding the above issues and other geotechnical design
considerations are provided in the following sections. These recommendations should be
incorporated into the final design drawings and construction specifications.
5.2 EARTHWORK
The earthwork is expected to include installing underground utilities excavating and
backfilling the residence foundations and preparing sidewalk, driveway and frontage
improvement roadway subgrades.
5.2.1 EROSION AND SEDIMENT CONTROL
Potential sources or causes of erosion and sedimentation depend on construction
methods, slope length and gradient, amount of soil exposed and/or disturbed, soil type,
Geotechnical Engineering Report 5 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
construction sequencing and weather. The impacts on erosion-prone areas can be
reduced by implementing an erosion and sedimentation control plan. The plan should be
designed in accordance with applicable city and/or county standards.
RGI recommends the following erosion control Best Management Practices (BMPs):
Scheduling site preparation and grading for the drier summer and early fall
months and undertaking activities that expose soil during periods of little or no
rainfall
Retaining existing vegetation whenever feasible
Establishing a quarry spall construction entrance
Installing siltation control fencing or anchored straw or coir wattles on the
downhill side of work areas
Covering soil stockpiles with anchored plastic sheeting
Revegetating or mulching exposed soils with a minimum 3-inch thickness of straw
if surfaces will be left undisturbed for more than one day during wet weather or
one week in dry weather
Directing runoff away from exposed soils and slopes
Minimizing the length and steepness of slopes with exposed soils and cover
excavation surfaces with anchored plastic sheeting (Graded and disturbed slopes
should be tracked in place with the equipment running perpendicular to the slope
contours so that the track marks provide a texture to help resist erosion and
channeling. Some sloughing and raveling of slopes with exposed or disturbed soil
should be expected.)
Decreasing runoff velocities with check dams, straw bales or coir wattles
Confining sediment to the project site
Inspecting and maintaining erosion and sediment control measures frequently
(The contractor should be aware that inspection and maintenance of erosion
control BMPs is critical toward their satisfactory performance. Repair and/or
replacement of dysfunctional erosion control elements should be anticipated.)
Permanent erosion protection should be provided by reestablishing vegetation using
hydroseeding and/or landscape planting. Until the permanent erosion protection is
established, site monitoring should be performed by qualified personnel to evaluate the
effectiveness of the erosion control measures. Provisions for modifications to the erosion
control system based on monitoring observations should be included in the erosion and
sedimentation control plan.
5.2.2 STRIPPING
Stripping efforts should include removal of pavements, vegetation, organic materials, and
deleterious debris from areas slated for building, pavement, and utility construction. The
hand augers encountered eight to 14 inches of topsoil and rootmass. Deeper areas of
stripping may be required in forested or heavily vegetated areas of the site.
Geotechnical Engineering Report 6 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
5.2.3 EXCAVATIONS
All temporary cut slopes associated with the site and utility excavations should be
adequately inclined to prevent sloughing and collapse. The site soils consist of dense
native soils.
Accordingly, for excavations more than 4 feet but less than 20 feet in depth, the
temporary side slopes should be laid back with a minimum slope inclination of 1.5H:1V
(Horizontal:Vertical) where groundwater seepage is encountered and 3/4H:1V in the
underlying dense soils. If there is insufficient room to complete the excavations in this
manner, or excavations greater than 20 feet in depth are planned, using temporary
shoring to support the excavations should be considered. For open cuts at the site, RGI
recommends:
No traffic, construction equipment, stockpiles or building supplies are allowed at
the top of cut slopes within a distance of at least five feet from the top of the cut
Exposed soil along the slope is protected from surface erosion using waterproof
tarps and/or plastic sheeting
Construction activities are scheduled so that the length of time the temporary cut
is left open is minimized
Surface water is diverted away from the excavation
The general condition of slopes should be observed periodically by a geotechnical
engineer to confirm adequate stability and erosion control measures
In all cases, however, appropriate inclinations will depend on the actual soil and
groundwater conditions encountered during earthwork. Ultimately, the site contractor
must be responsible for maintaining safe excavation slopes that comply with applicable
OSHA or WISHA guidelines.
5.2.4 SITE PREPARATION
Once stripping, clearing and other preparing operations are complete, the footings should
be excavated into the native soils. Subgrade soils that become disturbed due to elevated
moisture conditions should be overexcavated to reveal firm, non-yielding, non-organic
soils and backfilled with compacted structural fill. In order to maximize utilization of site
soils as structural fill, RGI recommends that the earthwork portion of this project be
completed during extended periods of warm and dry weather if possible. If earthwork is
completed during the wet season (typically November through May) it will be necessary
to take extra precautionary measures to protect subgrade soils. Wet season earthwork
will require additional mitigative measures beyond that which would be expected during
the drier summer and fall months.
Geotechnical Engineering Report 7 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
5.2.5 STRUCTURAL FILL
RGI recommends fill below the foundation and floor slab, behind retaining walls, and
below pavement and hardscape surfaces be placed in accordance with the following
recommendations for structural fill.
The suitability of excavated site soils and import soils for compacted structural fill use will
depend on the gradation and moisture content of the soil when it is placed. As the
amount of fines (that portion passing the U.S. No. 200 sieve) increases, soil becomes
increasingly sensitive to small changes in moisture content and adequate compaction
becomes more difficult or impossible to achieve. Soils containing more than about 5
percent fines cannot be consistently compacted to a dense, non-yielding condition when
the moisture content is more than 2 percent above or below optimum. Optimum
moisture content is that moisture that results in the greatest compacted dry density with
a specified compactive effort.
Non-organic site soils are only considered suitable for structural fill provided that their
moisture content is within about two percent of the optimum moisture level as
determined by ASTM D1557. Excavated site soils may not be suitable for re-use as
structural fill depending on the moisture content and weather conditions at the time of
construction. If soils are stockpiled for future reuse and wet weather is anticipated, the
stockpile should be protected with plastic sheeting that is securely anchored. Even during
dry weather, moisture conditioning (such as, windrowing and drying) of site soils to be
reused as structural fill may be required. Even during the summer, delays in grading can
occur due to excessively high moisture conditions of the soils or due to precipitation. If
wet weather occurs, the upper wetted portion of the site soils may need to be scarified
and allowed to dry prior to further earthwork, or may need to be wasted from the site.
The native soils were over the optimum moisture content during our explorations. The
native soils may require moisture conditioning even in the drier summer months. If on-
site soils are or become unusable or earthwork will be completed in wet weather, it may
become necessary to import clean, granular soils to complete site work that meet the
grading requirements listed in Table 2 to be used as structural fill.
Table 2 Structural Fill Gradation
U.S. Sieve Size Percent Passing
4 inches 100
No. 4 sieve 75 percent
No. 200 sieve 5 percent *
*Based on minus 3/4 inch fraction.
Geotechnical Engineering Report 8 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
Prior to use, an RGI representative should observe and test all materials imported to the
site for use as structural fill. Structural fill materials should be placed in uniform loose
layers not exceeding 12 inches and compacted as specified in Table 2. The soil’s maximum
density and optimum moisture should be determined by ASTM D1557.
Table 3 Structural Fill Compaction ASTM D1557
Location Material Type
Minimum
Compaction
Percentage
Moisture Content
Range
Foundations On-site granular or approved
imported fill soils: 95 +2 -2
Retaining Wall Backfill On-site granular or approved
imported fill soils: 92 +2 -2
Slab-on-grade On-site granular or approved
imported fill soils: 95 +2 -2
General Fill (non-
structural areas)
On-site soils or approved
imported fill soils: 90 +3 -2
Pavement – Subgrade
and Base Course
On-site granular or approved
imported fill soils: 95 +2 -2
Placement and compaction of structural fill should be observed by RGI. A representative
number of in-place density tests should be performed as the fill is being placed to confirm
that the recommended level of compaction is achieved.
5.2.6 CUT AND FILL SLOPES
All permanent cut and fill slopes (except interior slopes of detention pond) should be
graded with a finished inclination no greater than 2H:1V. The interior slopes of the
detention pond must be graded with a slope gradient no steeper than 3H:1V. Upon
completion of construction, the slope face should be trackwalked, compacted and
vegetated, or provided with other physical means to guard against erosion.
Final grades at the top of the slopes must promote surface drainage away from the slope
crest. Water must not be allowed to flow in an uncontrolled fashion over the slope face. If
it is necessary to direct surface runoff towards the slope, it should be controlled at the
top of the slope, piped in a closed conduit installed on the slope face, and taken to an
appropriate point of discharge beyond the toe of the slope. All fill placed for slope
construction should meet the structural fill requirements as described in Section 5.2.5.
5.2.7 WET WEATHER CONSTRUCTION CONSIDERATIONS
RGI recommends that preparation for site grading and construction include procedures
intended to drain ponded water, control surface water runoff, and to collect shallow
subsurface seepage zones in excavations where encountered. It will not be possible to
Geotechnical Engineering Report 9 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
successfully compact the subgrade or utilize on-site soils as structural fill if accumulated
water is not drained prior to grading or if drainage is not controlled during construction.
Attempting to grade the site without adequate drainage control measures will reduce the
amount of on-site soil effectively available for use, increase the amount of select import
fill materials required, and ultimately increase the cost of the earthwork phases of the
project. Free water should not be allowed to pond on the subgrade soils. RGI anticipates
that the use of berms and shallow drainage ditches, with sumps and pumps in utility
trenches, will be required for surface water control during wet weather and/or wet site
conditions.
5.3 FOUNDATIONS
Following site preparation and grading, the proposed residence foundations can be
supported on conventional spread footings bearing on medium dense to dense native soil
or structural fill. Loose, organic, or other unsuitable soils may be encountered in the
proposed building footprint. If unsuitable soils are encountered, they should be
overexcavated and backfilled with structural fill.
Perimeter foundations exposed to weather should be at a minimum depth of 18 inches
below final exterior grades. Interior foundations can be constructed at any convenient
depth below the floor slab. Finished grade is defined as the lowest adjacent grade within
5 feet of the foundation for perimeter (or exterior) footings and finished floor level for
interior footings.
Table 4 Foundation Design
Design Parameter Value
Allowable Bearing Capacity - Structural Fill
Dense native soils
2,500 psf1
4,000 psf
Friction Coefficient 0.30
Passive pressure (equivalent fluid pressure) 250 pcf2
Minimum foundation dimensions Columns: 24 inches
Walls: 16 inches
1. psf = pounds per square foot
2. pcf = pounds per cubic foot
The allowable foundation bearing pressures apply to dead loads plus design live load
conditions. For short-term loads, such as wind and seismic, a 1/3 increase in this
allowable capacity may be used. At perimeter locations, RGI recommends not including
the upper 12 inches of soil in the computation of passive pressures because they can be
affected by weather or disturbed by future grading activity. The passive pressure value
assumes the foundation will be constructed neat against competent soil or backfilled with
Geotechnical Engineering Report 10 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
structural fill as described in Section 5.2.5. The recommended base friction and passive
resistance value includes a safety factor of about 1.5.
With spread footing foundations designed in accordance with the recommendations in
this section, maximum total and differential post-construction settlements of 1 inch and
1/2 inch, respectively, should be expected.
5.4 RETAINING WALLS
If retaining walls are needed for the residences, RGI recommends cast-in-place concrete
walls be used. The magnitude of earth pressure development on retaining walls will partly
depend on the quality of the wall backfill. RGI recommends placing and compacting wall
backfill as structural fill. Wall drainage will be needed behind the wall face. A typical
retaining wall drainage detail is shown in Figure 3.
With wall backfill placed and compacted as recommended, and drainage properly
installed, RGI recommends using the values in the following table for design.
Table 5 Retaining Wall Design
Design Parameter Value
Allowable Bearing Capacity - Structural Fill
Dense native soils
2,500 psf
4,000 psf
Active Earth Pressure (unrestrained walls) 35 pcf
At-rest Earth Pressure (restrained walls) 50 pcf
For seismic design, an additional uniform load of 7 times the wall height (H) for
unrestrained walls and 14H in psf for restrained walls should be applied to the wall
surface.
Friction at the base of foundations and passive earth pressure will provide resistance to
these lateral loads. Values for these parameters are provided in Section 5.3.
5.5 SLAB-ON-GRADE CONSTRUCTION
Once site preparation has been completed as described in Section 5.2, suitable support
for slab-on-grade construction should be provided. RGI recommends that the concrete
slab be placed on top of medium dense native soil or structural fill. Immediately below
the floor slab, RGI recommends placing a four-inch thick capillary break layer of clean,
free-draining sand or gravel that has less than five percent passing the U.S. No. 200 sieve.
This material will reduce the potential for upward capillary movement of water through
the underlying soil and subsequent wetting of the floor slab. Where moisture by vapor
transmission is undesirable, an 8- to 10-millimeter thick plastic membrane should be
placed on a 4-inch thick layer of clean gravel.
Geotechnical Engineering Report 11 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
For the anticipated floor slab loading, we estimate post-construction floor settlements of
1/4- to 1/2-inch. For thickness design of the slab subjected to point loading from storage
racks, RGI recommends using a subgrade modulus (KS) of 150 pounds per square inch per
inch of deflection.
5.6 DRAINAGE
5.6.1 SURFACE
Final exterior grades should promote free and positive drainage away from the
residences. Water must not be allowed to pond or collect adjacent to foundations or
within the immediate building area. For non-pavement locations, RGI recommends
providing a minimum drainage gradient of 3 percent for a minimum distance of 10 feet
from the building perimeter. In paved locations, a minimum gradient of 1 percent should
be provided unless provisions are included for collection and disposal of surface water
adjacent to the structure.
5.6.2 SUBSURFACE
RGI recommends installing perimeter foundation drains. A typical footing drain detail is
shown on Figure 4. The foundation drains and roof downspouts should be tightlined
separately to an approved discharge facility. Subsurface drains must be laid with a
gradient sufficient to promote positive flow to a controlled point of approved discharge.
5.6.3 INFILTRATION
Infiltration is not feasible on the site due to the presence of nearly impermeable soils and
shallow groundwater conditions.
5.7 UTILITIES
Utility pipes should be bedded and backfilled in accordance with American Public Works
Association (APWA) specifications. For site utilities located within the right-of-ways,
bedding and backfill should be completed in accordance with City of Renton
specifications. At a minimum, trench backfill should be placed and compacted as
structural fill, as described in Section 5.2.5. Where utilities occur below unimproved
areas, the degree of compaction can be reduced to a minimum of 90 percent of the soil’s
maximum density as determined by the referenced ASTM D1557. As noted, soils
excavated on site may not be suitable for use as backfill material. Imported structural fill
meeting the gradation provided in Table 2 may be necessary for trench backfill.
5.8 PAVEMENTS
Pavement subgrades should be prepared as described in Section 5.2 and as discussed
below. Regardless of the relative compaction achieved, the subgrade must be firm and
relatively unyielding before paving. The subgrade should be proofrolled with heavy
construction equipment to verify this condition.
Geotechnical Engineering Report 12 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
With the pavement subgrade prepared as described above, RGI recommends the
following pavement sections for parking and drive areas paved with flexible asphalt
concrete surfacing.
For heavy truck traffic areas: 3 inches of Hot Mix Asphalt (HMA) over 6 inches of
crushed rock base (CRB)
For general parking areas: 2 inches of HMA over 4 inches of CRB
The asphalt paving materials used should conform to the Washington State Department
of Transportation (WSDOT) specifications for HMA and CRB surfacing.
Long-term pavement performance will depend on surface drainage. A poorly-drained
pavement section will be subject to premature failure as a result of surface water
infiltrating into the subgrade soils and reducing their supporting capability.
For optimum pavement performance, surface drainage gradients of no less than 2
percent are recommended. Also, some degree of longitudinal and transverse cracking of
the pavement surface should be expected over time. Regular maintenance should be
planned to seal cracks when they occur.
6.0 Additional Services
RGI is available to provide further geotechnical consultation throughout the design phase
of the project. RGI should review the final design and specifications in order to verify that
earthwork and foundation recommendations have been properly interpreted and
incorporated into project design and construction.
RGI is also available to provide geotechnical engineering and construction monitoring
services during construction. The integrity of the earthwork and construction depends on
proper site preparation and procedures. In addition, engineering decisions may arise in
the field in the event that variations in subsurface conditions become apparent.
Construction monitoring services are not part of this scope of work. If these services are
desired, please let us know and we will prepare a cost proposal.
7.0 Limitations
This GER is the property of RGI, Weston Heights, LLC, and its designated agents. Within
the limits of the scope and budget, this GER was prepared in accordance with generally
accepted geotechnical engineering practices in the area at the time this GER was issued.
This GER is intended for specific application to the Weston North project in Renton,
Washington, and for the exclusive use of Weston Heights, LLC and its authorized
representatives. No other warranty, expressed or implied, is made. Site safety, excavation
support, and dewatering requirements are the responsibility of others.
The scope of services for this project does not include either specifically or by implication
any environmental or biological (for example, mold, fungi, bacteria) assessment of the
Geotechnical Engineering Report 13 January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
site or identification or prevention of pollutants, hazardous materials or conditions. If the
owner is concerned about the potential for such contamination or pollution, we can
provide a proposal for these services.
The analyses and recommendations presented in this GER are based upon data obtained
from the test exploration performed on site. Variations in soil conditions can occur, the
nature and extent of which may not become evident until construction. If variations
appear evident, RGI should be requested to reevaluate the recommendations in this GER
prior to proceeding with construction.
It is the client’s responsibility to see that all parties to the project, including the designers,
contractors, subcontractors, are made aware of this GER in its entirety. The use of
information contained in this GER for bidding purposes should be done at the contractor’s
option and risk.
USGS, 2014, Mercer Island, Washington
USGS, 2014, Renton, Washington
7.5-Minute Quadrangle
Approximate Scale: 1"=1000'
0 500 1000 2000 N
Site Vicinity Map
Figure 1
01/2016
Corporate Office
17522 Bothell Way Northeast
Bothell, Washington 98011
Phone: 425.415.0551
Fax: 425.415.0311
Weston North
RGI Project Number
2016-009
Date Drawn:
Address: 702 Nile Avenue Northeast, Renton, Washington 98059
SITE
HA-1HA-2HA-301/2016Corporate Office17522 Bothell Way NortheastBothell, Washington 98011Phone: 425.415.0551Fax: 425.415.0311Weston NorthRGI Project Number2016-009Date Drawn:Address: 702 Nile Avenue Northeast, Renton, Washington 98059Geotechnical Exploration PlanFigure 2Approximate Scale: 1"=80'04080160N = HA-1 to HA-3 excavated by RGI, 1/22/16Drawn from Roadway and Drainage Plan by SDA, Civil Engineers
Incliniations)
12" Over the Pipe
3" Below the Pipe
Perforated Pipe
4" Diameter PVC
Compacted Structural
Backfill (Native or Import)
12" min.
Filter Fabric Material
12" Minimum Wide
Free-Draining Gravel
Slope to Drain
(See Report for
Appropriate
Excavated Slope
01/2016
Corporate Office
17522 Bothell Way Northeast
Bothell, Washington 98011
Phone: 425.415.0551
Fax: 425.415.0311
Weston North
RGI Project Number
2016-009
Date Drawn:
Address: 702 Nile Avenue Northeast, Renton, Washington 98059
Retaining Wall Drainage Detail
Figure 3
Not to Scale
3/4" Washed Rock or Pea Gravel
4" Perforated Pipe
Building Slab
Structural
Backfill
Compacted
Filter Fabric
01/2016
Corporate Office
17522 Bothell Way Northeast
Bothell, Washington 98011
Phone: 425.415.0551
Fax: 425.415.0311
Weston North
RGI Project Number
2016-009
Date Drawn:
Address: 702 Nile Avenue Northeast, Renton, Washington 98059
Typical Footing Drain Detail
Figure 4
Not to Scale
Geotechnical Engineering Report January 29, 2016
Weston North, Renton, Washington RGI Project No. 2016-009
APPENDIX A
FIELD EXPLORATION AND LABORATORY TESTING
On January 22, 2016, RGI performed field explorations using a hand auger. We explored
subsurface soil conditions at the site by excavating three hand augers to a maximum
depth of 3.5 feet below existing grade. The hand augers locations are shown on Figure 2.
The hand augers locations were approximately determined by measurements from
existing property lines and paved roads.
A geologist from our office conducted the field exploration and classified the soil
conditions encountered, maintained a log of each test exploration, obtained
representative soil samples, and observed pertinent site features. All soil samples were
visually classified in accordance with the Unified Soil Classification System (USCS).
Representative soil samples obtained from the explorations were placed in closed
containers and taken to our laboratory for further examination and testing. As a part of
the laboratory testing program, the soil samples were classified in our in house laboratory
based on visual observation, texture, plasticity, and the limited laboratory testing
described below.
Moisture Content Determinations
Moisture content determinations were performed in accordance with ASTM D2216-10
Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil
and Rock by Mass (ASTM D2216) on representative samples obtained from the
exploration in order to aid in identification and correlation of soil types. The moisture
content of typical sample was measured and is reported on the hand augers logs.
Grain Size Analysis
A grain size analysis indicates the range in diameter of soil particles included in a
particular sample. Grain size analyses was determined using D6913-04(2009) Standard
Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis (ASTM
D6913) on two of the samples.
THE RILEY GROUP, INC.
17522 Bothell Way NE
Bothell, WA 98011
PHONE: (425) 415-0551
FAX: (425) 415-0311
GRAIN SIZE ANALYSIS
ASTM D421, D422, D1140, D2487, D6913
PROJECT TITLE Weston North SAMPLE ID/TYPE HA-1 S-3
PROJECT NO.2016-009 SAMPLE DEPTH 3.5'
TECH/TEST DATE PL 1/22/2106 DATE RECEIVED 1/22/2016
WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture
Wt Wet Soil & Tare (gm) (w1)347.8 Weight Of Sample (gm)268.5
Wt Dry Soil & Tare (gm)(w2)268.5 Tare Weight (gm) 8.5
Weight of Tare (gm)(w3)8.5 (W6) Total Dry Weight (gm)260.0
Weight of Water (gm)(w4=w1-w2)79.3 SIEVE ANALYSIS
Weight of Dry Soil (gm) (w5=w2-w3)260.0 Cumulative
Moisture Content (%) (w4/w5)*100 31 Wt Ret (Wt-Tare) (%Retained)% PASS
+Tare {(wt ret/w6)*100}(100-%ret)
% COBBLES 0.0 12.0"8.5 0.00 0.00 100.00 cobbles
% C GRAVEL 0.0 3.0"8.5 0.00 0.00 100.00 coarse gravel
% F GRAVEL 1.3 2.5" coarse gravel
% C SAND 2.7 2.0" coarse gravel
% M SAND 6.7 1.5"8.5 0.00 0.00 100.00 coarse gravel
% F SAND 6.5 1.0" coarse gravel
% FINES 82.8 0.75"8.5 0.00 0.00 100.00 fine gravel
% TOTAL 100.0 0.50" fine gravel
0.375"8.5 0.00 0.00 100.00 fine gravel
D10 (mm)#4 11.8 3.30 1.27 98.73 coarse sand
D30 (mm)#10 18.8 10.30 3.96 96.04 medium sand
D60 (mm)#20 medium sand
Cu #40 36.1 27.60 10.62 89.38 fine sand
Cc #60 fine sand
#100 47.4 38.90 14.96 85.04 fine sand
#200 53.1 44.60 17.15 82.85 fines
PAN 268.5 260.00 100.00 0.00 silt/clay
DESCRIPTION SILT with some sand
USCS ML
Prepared For:Reviewed By:KMW
Weston Heights, LLC
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.11101001000
%
P
A
S
S
I
N
G
Grain size in millimeters
12"3"2"1".75".375"#4 #10 #20 #40 #60 #100 #200
THE RILEY GROUP, INC.
17522 Bothell Way NE
Bothell, WA 98011
PHONE: (425) 415-0551
FAX: (425) 415-0311
GRAIN SIZE ANALYSIS
ASTM D421, D422, D1140, D2487, D6913
PROJECT TITLE Weston North SAMPLE ID/TYPE HA-2 S-2
PROJECT NO.2016-009 SAMPLE DEPTH 2'
TECH/TEST DATE PL 1/22/2106 DATE RECEIVED 1/22/2016
WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture
Wt Wet Soil & Tare (gm) (w1)322.0 Weight Of Sample (gm)238.0
Wt Dry Soil & Tare (gm)(w2)238.0 Tare Weight (gm) 8.4
Weight of Tare (gm)(w3)8.4 (W6) Total Dry Weight (gm)229.6
Weight of Water (gm)(w4=w1-w2)84.0 SIEVE ANALYSIS
Weight of Dry Soil (gm) (w5=w2-w3)229.6 Cumulative
Moisture Content (%) (w4/w5)*100 37 Wt Ret (Wt-Tare) (%Retained)% PASS
+Tare {(wt ret/w6)*100}(100-%ret)
% COBBLES 0.0 12.0"8.4 0.00 0.00 100.00 cobbles
% C GRAVEL 0.0 3.0"8.4 0.00 0.00 100.00 coarse gravel
% F GRAVEL 15.4 2.5" coarse gravel
% C SAND 11.7 2.0" coarse gravel
% M SAND 13.9 1.5"8.4 0.00 0.00 100.00 coarse gravel
% F SAND 21.6 1.0" coarse gravel
% FINES 37.4 0.75"8.4 0.00 0.00 100.00 fine gravel
% TOTAL 100.0 0.50" fine gravel
0.375"17.6 9.20 4.01 95.99 fine gravel
D10 (mm)#4 43.8 35.40 15.42 84.58 coarse sand
D30 (mm)#10 70.7 62.30 27.13 72.87 medium sand
D60 (mm)#20 medium sand
Cu #40 102.6 94.20 41.03 58.97 fine sand
Cc #60 fine sand
#100 133.2 124.80 54.36 45.64 fine sand
#200 152.1 143.70 62.59 37.41 fines
PAN 238.0 229.60 100.00 0.00 silt/clay
DESCRIPTION Silty SAND with some gravel
USCS SM
Prepared For:Reviewed By:KMW
Weston Heights, LLC
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.11101001000
%
P
A
S
S
I
N
G
Grain size in millimeters
12"3"2"1".75".375"#4 #10 #20 #40 #60 #100 #200