HomeMy WebLinkAboutRS_Geotechnical_Report_190315_v1.pdfGeotechnical Engineering Services
Willow Crest Townhomes
Renton, Washington
for
Homestead Community Land Trust
c/o Third Place Design Co-operative
November 15, 2018
Geotechnical Engineering Services
Willow Crest Townhomes
Renton, Washington
for
Homestead Community Land Trust
c/o Third Place Design Co-operative
November 15, 2018
17425 NE Union Hill Road, Suite 250
Redmond, Washington 98052
425.861.6000
Prepared for:
Homestead Community Land Trust
c/o Third Place Design Co-operative
177 Western Avenue West, Suite 266
Seattle, Washington 98119
Geotechnical Engineering Services
Willow Crest Townhomes
Renton, Washington
File No. 23656-001-00
November 15, 2018
Attention: Suzanne Davis, LEED AP, NCARB
Prepared by:
GeoEngineers, Inc.
17 425 NE Union Hill Road, Suite 250
Redmond, Washington 98052
425.861.6000
Michael A. Gray, PE
Geotechnical Engineer
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Principal
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GEoENGINEER�
November 15, 2018 | Page i File No. 23656-001-00
Table of Contents
INTRODUCTION ..................................................................................................................................................... 1
Project Description ........................................................................................................................................... 1
Purpose and Scope .......................................................................................................................................... 1
FIELD EXPLORATIONS AND LABORATORY TESTING ......................................................................................... 1
Field Explorations ............................................................................................................................................. 1
Laboratory Testing ........................................................................................................................................... 1
Previous Studies .............................................................................................................................................. 2
SITE DESCRIPTIONS............................................................................................................................................. 2
Site Geology ..................................................................................................................................................... 2
Surface Conditions........................................................................................................................................... 2
Subsurface Conditions .................................................................................................................................... 2
Groundwater Conditions .................................................................................................................................. 3
CONCLUSIONS AND RECOMMENDATIONS ........................................................................................................ 3
Summary .......................................................................................................................................................... 3
Earthquake Engineering .................................................................................................................................. 4
2015 IBC Seismic Design Information .................................................................................................... 4
Liquefaction Potential ............................................................................................................................... 4
Ground Rupture ......................................................................................................................................... 4
Landslides ................................................................................................................................................. 5
Foundations ..................................................................................................................................................... 5
Foundation Design .................................................................................................................................... 5
Foundation Settlement ............................................................................................................................. 5
Lateral Resistance .................................................................................................................................... 6
Construction Considerations .................................................................................................................... 6
Footing Drains ........................................................................................................................................... 6
Slab-on-Grade Floors ....................................................................................................................................... 6
Pavement Recommendations ......................................................................................................................... 7
Subgrade Preparation ............................................................................................................................... 7
New Hot Mix Asphalt Pavement ............................................................................................................... 7
Portland Cement Concrete Pavement ..................................................................................................... 8
Asphalt-Treated Base ................................................................................................................................ 8
Earthwork ......................................................................................................................................................... 8
Clearing and Site Preparation .................................................................................................................. 9
Subgrade Preparation ............................................................................................................................... 9
Structural Fill ........................................................................................................................................... 10
Permanent Cut and Fill Slopes ............................................................................................................... 12
Utility Trenches ........................................................................................................................................ 12
Sedimentation and Erosion Control ....................................................................................................... 13
Excavations .................................................................................................................................................... 13
Temporary Cut Slopes ............................................................................................................................. 13
Drainage Considerations ............................................................................................................................... 14
November 15, 2018 | Page ii File No. 23656-001-00
Infiltration Considerations ............................................................................................................................. 14
RECOMMENDED ADDITIONAL GEOTECHNICAL SERVICES ............................................................................. 15
LIMITATIONS ....................................................................................................................................................... 15
REFERENCES ..................................................................................................................................................... 15
LIST OF FIGURES
Figure 1. Vicinity Map
Figure 2. Site Plan – Proposed Development
Figure 3. Compaction Criteria for Trench Backfill
APPENDICES
Appendix A. Field Explorations
Figure A-1. Key to Exploration Logs
Figures A-2 through A-7. Logs of Test Pits
Appendix B. Laboratory Testing
Figures B-1 and B-2. Sieve Analysis Results
Figure B-3. Compaction Test Results (TP-3)
Appendix C. Boring and Test Pit Logs from Previous Studies
Appendix D. Report Limitations and Guidelines for Use
November 15, 2018 | Page 1
File No. 23656-001-00
INTRODUCTION
This report presents the results of GeoEngineers, Inc.’s (GeoEngineers) geotechnical engineering services
for the Willow Crest Townhomes project located in Renton, Washington. The site is shown relative to
surrounding physical features on Figure 1, Vicinity Map and Figure 2, Site Plan.
Project Description
We understand that the proposed development will consist of three four-unit wood-frame townhomes
(12 total townhomes) constructed at existing grade. The development will also include new underground
utilities, access drive, sidewalks, and landscaping. Minor site grading is anticipated and no underground
structures are planned for the project.
Purpose and Scope
The purpose of our geotechnical engineering services is to evaluate soil and groundwater conditions as a
basis for developing design criteria for the geotechnical aspects of the proposed development. Field
explorations and laboratory testing were performed to identify and evaluate subsurface conditions at the
sites to develop engineering recommendations for use in design of the project. Our services were performed
in general accordance with our scope of services outlined in our Proposal dated October 2, 2018.
FIELD EXPLORATIONS AND LABORATORY TESTING
Field Explorations
The subsurface soil and groundwater conditions were evaluated by reviewing existing geotechnical
information and completing six test pits (GEI-TP-1 through GEI-TP-6) across the planned building locations.
The test pits were completed to depths of approximately 8 feet below the ground surface (bgs). The test
pits were completed on October 22, 2018 using a rubber-tracked backhoe. The approximate locations of
the explorations are shown on Figure 2. Descriptions of the field exploration program and the explorations
logs are presented in Appendix A.
Laboratory Testing
Soil samples were obtained during the exploration program and taken to our laboratory for further
evaluation. Selected samples were tested for the determination of moisture content, fines content, grain
size distribution (sieve analysis), and modified Proctor compaction tests. A description of the laboratory
testing and the test results are presented in Appendix B.
November 15, 2018 | Page 2 File No. 23656-001-00
Previous Studies
The exploration logs (borings and test pits) of selected explorations from previous subsurface studies in
vicinity of the proposed project were reviewed. Logs of relevant explorations reviewed for this study are
presented in Appendix C and approximate locations are shown on Figure 2. The existing subsurface
information includes:
■ “Report of Geotechnical Investigation, Proposed Residential Development, Edmonds and
Glennwood Ave NE, Renton, Washington,” prepared by Soil and Environmental Engineers, Inc., dated
January 10, 2011.
SITE DESCRIPTIONS
Site Geology
Our review of the geologic map for the area (Mullineaux 1965) and previous geotechnical reports completed
in the vicinity of the project site indicate that the proposed development is underlain by dense to very dense
glacial till at relatively shallow depths. Dense to very dense native glacial till was observed in all the test
pits completed at the site. Glacial till commonly consists of a very compact, poorly sorted, non-stratified
mixture of clay, silt, sand, gravel and cobbles. Glacial till commonly appears gray or blue on a fresh surface,
while weathered glacial till may be brown to yellow in color. The till was observed to contain cobbles in some
areas and commonly also includes large boulders. Additionally, test pit GEI-TP-4 encountered a boulder at
approximately 3.5 feet.
Surface Conditions
The location of the proposed townhomes consists of an undeveloped lot covered with vegetation. The lot is
relatively flat and slopes down from approximate Elevation 343 feet in the northeast corner to about
Elevation 330 feet in the southwest corner. Vegetation generally consists of blackberry brambles with
various deciduous trees spread across the site. An existing storm drain outfall is present in the southeast
corner of the site.
Subsurface Conditions
Shallow fill overlying loose to medium dense weathered glacial till and dense to very dense relatively
unweathered native glacial till was observed in all of our test pits completed at the planned townhome
locations. In general, the soils encountered in the test pits consisted of the following:
Fill: Fill consisting of loose to medium dense sand with silt and gravel exists across the site. The fill is
relatively thin and is typically less than 1 foot deep in the test pits completed at the project site.
Till: Glacial till was observed to the depths explored in all of the test pits. The glacial till is relatively
unweathered at a depth ranging from about 2.5 to 3.5 feet bgs and consists of gray dense to very dense
silty fine to medium sand with variable gravel content and occasional cobbles. Weathered glacial till exists
near the ground surface below the fill and above the relatively unweathered parent material and is typically
brown and loose to medium dense. The weathered till may be 1 to 3 feet thick across the site.
November 15, 2018 | Page 3 File No. 23656-001-00
Groundwater Conditions
No groundwater seepage was observed in the test pits completed on site. Additionally, previous
explorations completed to depths of 30 feet below site grades did not encounter groundwater.
Groundwater observations represent conditions observed during exploration and may not represent the
groundwater conditions throughout the year. We anticipate that perched groundwater will exist at the
contact between the glacial till and the overlying looser fill and weathered till, and within more permeable
layers within the native glacial till. Groundwater seepage is expected to fluctuate as a result of season,
precipitation, and other factors.
CONCLUSIONS AND RECOMMENDATIONS
Based on the results of our field exploration program, laboratory testing, and engineering analysis, we
conclude that development of the proposed development can be accomplished as planned. A summary of
primary geotechnical considerations for the site development and design of the proposed development is
provided in the subsequent sections.
Summary
■ The planned townhomes site is classified as Site Class C, in accordance with the 2015 International
Building Code (IBC).
■ The planned townhomes may be supported on conventional spread footings bearing on dense to very
dense undisturbed glacial till or on structural fill placed over these soils. Footings bearing on dense to
very dense undisturbed glacial till may be designed using an allowable soil bearing value of
6,000 pounds per square foot (psf). Footings bearing on structural fill placed over undisturbed dense
to very dense glacial till may be designed using an allowable bearing value of 3,000 psf. All existing fill,
highly weathered glacial till or otherwise unsuitable soils should be removed from below foundations
prior to constructing foundations or placing structural fill. The allowable bearing value may be increased
by one-third for short duration loads such as wind or seismic events.
■ Lateral foundation loads may be resisted by passive resistance on the sides of the footings and by
friction on the base of the footings. For footings supported and surrounded by either dense native soils
or compacted structural fill, a coefficient of friction of 0.35 and a passive resistance of 350 pounds per
cubic foot (pcf) may be used.
■ A subgrade modulus of 100 pounds per cubic inch (pci) may be used for design of the slabs-on-grade
for the townhomes. Concrete slabs-on-grade should be supported on a 4-inch-thick capillary break layer
overlain by a vapor retarder (in conditioned spaces or enclosed rooms, such as mechanical or storage
space).
■ The pavement section extending to the west and north from the southeast corner of the project site
may be supported on existing fill soils provided that the upper 2 feet of the fill is placed and compacted
as structural fill. A proof roll test can also be conducted to reduce excavation costs if native soils are
encountered within the upper 2 feet and to check that the soils can perform adequately under planned
loads. If any soft spots are observed, the upper 2 feet of subgrade soils should be removed and
replaced with at least 2 feet of structural fill compacted to at least 95 percent of the maximum dry
density (MDD) per ASTM International (ASTM) D 1557. Suitable on-site soils may be used as structural
November 15, 2018 | Page 4 File No. 23656-001-00
fill under the planned road and associated hardscape provided that earthwork is accomplished during
dry weather conditions in the summer months.
Earthquake Engineering
We evaluated the site for seismic hazards including liquefaction, lateral spreading, fault rupture and
earthquake-induced landsliding. Our evaluation indicates that the site does not have liquefiable soils
present and, therefore, also has no risk of liquefaction-induced lateral spreading. In addition, the site has
a low risk of fault rupture and earthquake-induced landsliding.
2015 IBC Seismic Design Information
For the planned townhomes, we recommend the IBC 2015 parameters for average field standard
penetration resistance, site class, short period spectral response acceleration (SS), 1-second period
spectral response acceleration (S1), and seismic coefficients FA and FV presented in Table 1.
TABLE 1. 2015 IBC SEISMIC PARAMETERS
2015 IBC Parameter Recommended Value
Average Field Standard Penetration Resistance >50
Site Class C
Short Period Spectral Response Acceleration, SS (percent g) 143.2
1-Second Period Spectral Response Acceleration, S1 (percent g) 53.8
Seismic Coefficient, FA 1.000
Seismic Coefficient, FV 1.300
Liquefaction Potential
Liquefaction is a phenomenon where soils experience a rapid loss of internal strength as a consequence
of strong ground shaking. Ground settlement, lateral spreading and/or sand boils may result from soil
liquefaction. Structures supported on liquefied soils could suffer foundation settlement or lateral
movement that could be severely damaging to the structures.
Conditions favorable to liquefaction occur in loose to medium dense, clean to moderately silty sand, which
is below the groundwater level. Based on our evaluation of the subsurface conditions observed in the
explorations, it is our opinion that potentially liquefiable soils are not present at the project site.
Ground Rupture
Ground rupture from lateral spreading is associated with liquefaction. Lateral spreading involves lateral
displacements of large volumes of liquefied soil, and can occur on near-level ground as blocks of surface
soils displace relative to adjacent blocks. In our opinion, ground rupture resulting from lateral spreading at
the site is unlikely because potentially liquefiable soils are not present at the site as discussed above.
Because of the thickness of the Quaternary sediments below the site, which are commonly more than
1,000 feet thick, the potential for surface fault rupture is considered low.
November 15, 2018 | Page 5 File No. 23656-001-00
Landslides
Because site topography is relatively flat and dense to very dense glacial till deposits occur at shallow
depths, it is our opinion that landsliding as a result of strong ground shaking is unlikely at the site.
Foundations
We recommend that the buildings be supported on shallow spread footings founded on the dense to very
dense native glacial till soil encountered in the explorations, or on properly compacted structural fill
extending down to medium dense to dense glacial till. The following recommendations for the buildings are
based on the subsurface conditions observed in the explorations and the site survey.
Foundation Design
For shallow foundation support, we recommend widths of at least 18 and 24 inches, respectively, for
continuous wall and isolated column footings supporting the proposed townhomes. The design frost depth
in the Puget Sound area is 12 inches, therefore, we recommend that the footings be founded at least
18 inches below lowest adjacent finished grade.
Unsuitable soils consisting of fill, topsoil, and/or highly weathered glacial soils will vary across the site and
must be removed from below planned footings. Based on our explorations, up to 3½ feet of fill and/or
looser weathered native soils exist under the proposed north building unit (GEI-TP-1 and GEI-TP-2),
approximately 3 feet under the central building unit (GEI-TP-3 and GEI-TP-4) and 2½ feet under the south
building unit (GEI-TP-5 and GEI-TP-6). Therefore, depending on the foundation locations and depths,
overexcavation under the footings may be necessary. For foundations supported on medium dense native
glacial till or structural fill extending down to medium dense to dense native glacial till, we recommend
footings be designed using a maximum allowable bearing pressure of 3,000 psf. A maximum allowable
bearing pressure of 6,000 psf may be used in design where foundations are bearing on dense to very dense
relatively unweathered glacial till or on controlled density fill (CDF) extending down to the dense to very
dense native till. All existing fill and looser native soils should be removed from below planned footings.
These allowable bearing pressures apply to the total dead and long-term live loads and may be increased
up to one-third for short-term live loads such as wind or seismic forces.
The overexcavated areas should be backfilled with: (1) CDF having a design strength of at least 200 pounds
per square inch (psi) where 6,000 psf bearing pressures are used or, (2) imported gravel borrow where
3,000 psf is used. Where structural fill is placed below footings, the fill should extend beyond the edges of
the foundations by the depth of the overexcavation, while the CDF should extend beyond the edges of the
foundations by half the depth of the excavation.
Foundation Settlement
We estimate that the post-construction settlement of footings founded on the very dense glacial till or
structural fill extending to the medium dense to very dense till, as recommended above, will be between
½ and 1 inch. Differential settlement between comparably loaded column footings or along a 25-foot
section of continuous wall footing should be less than ½ inch. We expect most of the footing settlements
will occur as loads are applied. Loose or disturbed soils not removed from footing excavations prior to
placing concrete will result in additional settlement.
November 15, 2018 | Page 6 File No. 23656-001-00
Lateral Resistance
Lateral loads can be resisted by passive resistance on the sides of the footings and by friction on the base
of the footings. Passive resistance should be evaluated using an equivalent fluid density of 350 pcf where
footings are poured neat against native soil or are surrounded by structural fill compacted to at least
95 percent of MDD, as recommended. Resistance to passive pressure should be calculated from the
bottom of adjacent floor slabs and paving or below a depth of 1 foot where the adjacent area is unpaved,
as appropriate. Frictional resistance can be evaluated using 0.35 for the coefficient of base friction against
footings. The above values incorporate a factor of safety of about 1.5.
If soils adjacent to footings are disturbed during construction, the disturbed soils must be recompacted,
otherwise the lateral passive resistance value must be reduced.
Construction Considerations
Immediately prior to placing concrete, all debris and loose soils that accumulated in the footing excavations
during forming and steel placement must be removed. Debris or loose soils not removed from the footing
excavations will result in increased settlement.
If wet weather construction is planned, we recommend that all footing subgrades be protected using a lean
concrete mud mat or 3 inches of compacted crushed base course. The mud mat or base course should be
placed the same day that the footing subgrade is excavated and approved for foundation support.
We recommend that all completed footing excavations be observed by a representative of our firm prior to
placing mud mat, reinforcing steel, and structural concrete. Our representative will confirm that the bearing
surface has been prepared in a manner consistent with our recommendations and that the subsurface
conditions are as expected.
Footing Drains
We recommend that perimeter footing drains be installed around each building. The perimeter drains
should be installed at the base of the exterior footings. The perimeter drains should be provided with
cleanouts and should consist of at least 4-inch-diameter perforated pipe placed on a 3-inch bed of drainage
material, and surrounded by 6 inches of drainage material enclosed in a non-woven geotextile fabric such
as TenCate Mirafi 140N (or approved equivalent) to prevent fine soil from migrating into the drain material.
We recommend against using flexible tubing for footing drainpipes. The perimeter drains should be sloped
to drain by gravity, if practicable, to a suitable discharge point, preferably a storm drain. We recommend
that the cleanouts be covered, and be placed in flush-mounted utility boxes. Water collected in roof
downspout lines must not be routed to the footing drain lines.
Slab-on-Grade Floors
We expect that the lower level concrete slab-on-grade can be supported on the medium dense to very dense
native soil encountered in our explorations or on properly compacted structural fill. A subgrade modulus of
100 pci may be used for design of the slabs-on-grade at the site. We recommend that an appropriate
capillary break and vapor retarder be installed below concrete slabs to reduce the risk of moisture migration
through the floor slab. This is especially important since zones of groundwater seepage may be present at
the planned floor slab level in more permeable layers above the dense native glacial till or in looser soils
on top of the dense glacial till.
November 15, 2018 | Page 7 File No. 23656-001-00
Prior to placing the gravel layer, the subgrade should be proofrolled as described previously in the
“Earthwork” section of this report. If necessary, the building slab subgrades should be recompacted to a
firm and unyielding condition.
We recommend that concrete slabs-on-grade be constructed on a gravel layer to provide uniform support
and drainage and to act as a capillary break. The gravel layer below slabs-on-grade should consist of at
least 4 inches of clean crushed gravel with a maximum particle size of 1 inch and negligible sand or silt in
accordance with Washington State Department of Transportation (WSDOT) Standard Specification
9-03.1(4)C American Association of State Highway and Transportation Officials (AASHTO) Grading No. 67.
If prevention of moisture migration through the slab is essential, a vapor retarder such as heavy plastic
sheeting should be installed between the slab and the gravel layer. It may also be prudent to apply a sealer
to the slab to further retard the migration of moisture through the floor. We recommend that the plastic
sheet be placed over the capillary break layer.
Pavement Recommendations
Recommendations for typical pavements (asphalt and concrete) are provided in the following sections. The
City of Renton may have standard pavement sections that could apply to the site, therefore the project civil
engineer should review the City’s standards, if applicable.
Subgrade Preparation
We recommend the subgrade soils in new pavement areas be prepared and evaluated as described in the
“Earthwork” section of this report. All new pavement and hardscape areas should be supported on
subgrade soils that have been proof rolled or probed as described in the “Clearing and Site Preparation”
section of this report. If the exposed subgrade soils are loose or soft, it may be necessary to excavate
localized areas and replace them with structural fill or gravel base course. Pavement subgrade conditions
should be observed during construction and prior to placing the subbase materials in order to evaluate the
presence of zones of unsuitable subgrade soils and the need for overexcavation and replacement of these
zones.
New Hot Mix Asphalt Pavement
In light-duty pavement areas (e.g., automobile parking), we recommend a pavement section consisting of
at least a 2½ -inch thickness of ½-inch hot-mix asphalt (HMA) per WSDOT Sections 5-04 and 9-03,
over a 4-inch thickness of densely compacted crushed surfacing base course (CSBC) per WSDOT Section
9-03.9(3). In heavy-duty pavement areas (such as the driveway), we recommend a pavement section
consisting of at least a 3-inch thickness of ½-inch HMA over a 6-inch thickness of densely compacted CSBC.
The base course should be compacted to at least 95 percent of the MDD obtained using ASTM D 1557.
We recommend that proof rolling of the subgrade and compacted base course be observed by a
representative from our firm prior to paving. Soft or yielding zones observed during proof rolling may require
overexcavation and replacement with compacted structural fill.
The pavement sections recommended above are based on our experience. Thicker asphalt sections may
be needed in accordance with the City of Renton or based on the actual traffic data, truck loads, and
intended use. All paved and landscaped areas should be graded so that surface drainage is directed to
appropriate catch basins.
November 15, 2018 | Page 8 File No. 23656-001-00
Portland Cement Concrete Pavement
Portland cement concrete (PCC) sections may be considered for areas where concentrated heavy loads
may occur. We recommend that these pavements consist of at least 6 inches of PCC over 6 inches of CSBC.
A thicker concrete section may be needed based on the actual load data for use of the area. If the concrete
pavement will have doweled joints, we recommend that the concrete thickness be increased by an amount
equal to the diameter of the dowels. The base course should be compacted to at least 95 percent of the
MDD.
We recommend PCC pavements incorporate construction joints and/or crack control joints spaced at
maximum distances of 12 feet apart, center-to-center, in both the longitudinal and transverse directions.
Crack control joints may be created by placing an insert or groove into the fresh concrete surface during
finishing, or by saw cutting the concrete after it has initially set up. We recommend the depth of the crack
control joints be approximately one fourth the thickness of the concrete; or about 1½ inches deep for the
recommended concrete thickness of 6 inches. We also recommend the crack control joints be sealed with
an appropriate sealant to help restrict water infiltration into the joints.
Asphalt-Treated Base
If pavements are constructed during the wet seasons, consideration may be given to covering the areas to
be paved with asphalt-treated base (ATB) for protection. Light-duty pavement areas should be surfaced with
3 inches of ATB, and heavy-duty pavement areas should be surfaced with 6 inches of ATB. Thicker ATB
sections may be needed based on construction equipment loads. Prior to placement of the final pavement
sections, we recommend the ATB surface be evaluated and areas of ATB pavement failure be removed and
the subgrade repaired. If ATB is used and is serviceable when final pavements are constructed, the CSBC
can be eliminated, and the design PCC or asphalt concrete pavement thickness can be placed directly over
the ATB.
Earthwork
Based on the subsurface soil conditions encountered in the explorations, we expect that the soils at the
site may be excavated using conventional heavy-duty construction equipment. Very dense glacial till was
encountered at relatively shallow depths at the planned building locations; therefore, glacial till soils within
deeper portions of excavations may require a large excavator to accomplish the excavations. Cobbles were
observed in most of the test pits and glacial till deposits in the area commonly contain boulders that may
be encountered during excavation. Accordingly, the contractor should be prepared to deal with boulders, if
encountered.
The glacial till contains sufficient fines (material passing the U.S. standard No. 200 sieve) to be highly
moisture-sensitive and susceptible to disturbance, especially when wet. Ideally, earthwork should be
undertaken during extended periods of dry weather when the surficial soils will be less susceptible to
disturbance and provide better support for construction equipment. Dry weather construction will help
reduce earthwork costs and increase the potential for using the native soils as structural fill.
Trafficability on the site is not expected to be difficult during dry weather conditions. However, the fill and
native soils will be susceptible to disturbance from construction equipment during wet weather conditions
and pumping and rutting of the exposed soils under equipment loads may occur.
November 15, 2018 | Page 9 File No. 23656-001-00
Clearing and Site Preparation
Areas to be developed or graded should be cleared of surface and subsurface deleterious matter including
any debris, shrubs, trees and associated stumps and roots. Graded areas should be stripped of organic
soils.
The organic soils can be stockpiled and used later for landscaping purposes or may be spread over
disturbed areas following completion of grading. If spread out, the organic strippings should be in a layer
less than 1-foot thick, should not be placed on slopes greater than 3H:1V (horizontal to vertical) and should
be track-rolled to a uniformly compacted condition. Materials that cannot be used for landscaping or
protection of disturbed areas should be removed from the project site.
Undocumented fill may be present in various areas of the site and will be required to be removed under
building foundations and within the upper two feet of pavement, hardscape and slab subgrade levels.
Where existing fill and looser native soils are removed, they may be reused and recompacted as structural
fill, if conditions allow. If medium dense to dense native soils are encountered below slab subgrade,
additional excavation is not required. If old fill is encountered below slab subgrade, the fill should be
evaluated and possibly removed up to 2 feet below slab subgrade or until medium dense to dense native
soils are encountered (less than 2 feet below slab subgrade). Excavations for slab subgrade preparation
likely do not need to extend more than 2 feet below slab subgrade. The upper two feet below pavement
subgrade should also be removed and replaced as structural fill; however, if existing fill soils are suitable
and adequately compacted based on evaluations after the pavement is removed, the contractor can
perform a proof roll on the exposed surface at or below slab subgrade level, and if approved by the
geotechnical engineer, the fill may be left in place.
Subgrade Preparation
Prior to placing new fills, pavement base course materials or gravel below on-grade floor slabs, subgrade
areas should be proof rolled to locate any soft or pumping soils. Prior to proof rolling, all unsuitable soils
should be removed from below the building footprints. Proof rolling can be completed using a piece of heavy
tire-mounted equipment such as a loaded dump truck. During wet weather, the exposed subgrade areas
should be probed to determine the extent of soft soils. If soft or pumping soils are observed, they should
be removed and replaced with compacted structural fill.
If deep pockets of soft or pumping soils are encountered outside the building areas, it may be possible to
limit the depth of overexcavation by placing a non-woven geotextile fabric such as TenCate Mirafi 500X (or
equivalent) on the overexcavated subgrade prior to placing structural fill. The geotextile will provide
additional support by bridging over the soft material and will help reduce fines contamination into the
structural fill.
After completing the proof rolling, the subgrade areas should be recompacted to a firm and unyielding
condition, if possible. The degree of compaction that can be achieved will depend on when the construction
is performed. If the work is performed during dry weather conditions, we recommend that all subgrade
areas be recompacted to at least 95 percent of the MDD in accordance with the ASTM D 1557 test
procedure (modified Proctor). If the work is performed during wet weather conditions, it may not be possible
to recompact the subgrade to 95 percent of the MDD. In this case, we recommend that the subgrade be
compacted to the extent possible without causing undue heaving or pumping of the subgrade soils.
November 15, 2018 | Page 10 File No. 23656-001-00
Subgrade disturbance or deterioration could occur if the subgrade is wet and cannot be dried. If the
subgrade deteriorates during proof rolling or compaction, it may become necessary to modify the proof
rolling, compaction criteria, or methods.
Structural Fill
All fill, whether existing on-site glacial till soil or imported soil, that will support building foundations and
floor slabs, pavement and hardscape areas, or be placed in utility trenches should generally meet the
criteria for structural fill presented below. The suitability of soil for use as structural fill depends on its
gradation and moisture content.
Materials
Materials used on the project site, under buildings, pavement, hardscape areas, and to backfill utility
trenches are classified as structural fill for the purpose of this report. Structural fill material quality varies
depending upon its use as described below:
1. Structural fill placed below all building elements (except footing designed for greater than 3,000 psf
bearing pressure) and during wet weather conditions should consist of imported Gravel Borrow, as
described in Section 9-03.14(1) of the 2018 WSDOT Standard Specifications, with the additional
restriction that the fines content be limited to no more than 5 percent. On-site soils may be used as
structural fil provided it is placed during the summer months, is properly moisture conditioned to within
2 percent of the optimum moisture content, and can be compacted to at least 95 percent of the MDD.
2. CDF having a design strength of at least 200 psi should be used under all foundations designed for
greater than 3,000 psf bearing pressure.
3. Structural fill placed to construct embankment and parking areas and to backfill utility trenches may
consist of on-site fill and glacial till provided that the soils are moisture conditioned for the required
compaction. On-site till soils may be suitable for use as structural fill during dry weather conditions in
areas needing 95 percent compaction. If structural fill is placed during wet weather, the structural fill
should consist of imported gravel borrow.
4. Structural fill placed as CSBC below pavements should conform to Section 9-03.9(3) of the 2018
WSDOT Standard Specifications.
5. Structural fill placed as capillary break below slabs should consist of 1-inch minus clean crushed gravel
with negligible sand or silt in conformance with Section 9-03.1(4)C, grading No. 67 of the 2018 WSDOT
Standard Specifications.
Reuse of On-site Native Soils
The existing fill and till soils contain a high percentage of fines and will be sensitive to changes in moisture
content and difficult to handle and compact during wet weather.
The existing fill (free of organic debris) and till deposits are expected to be suitable for structural fill in areas
requiring compaction to at least 95 percent of MDD (per ASTM D 1557), provided the work is accomplished
during the normally dry season (June through September) and that the soil can be properly moisture
conditioned to within 2 percent of the optimum moisture content. Imported structural fill consisting of sand
and gravel (WSDOT gravel borrow) should be planned under all building foundation elements, especially if
construction occurs during wet weather.
November 15, 2018 | Page 11 File No. 23656-001-00
The use of existing on-site fill and till soils as structural fill during wet weather should be planned only for
areas requiring compaction to 90 percent of MDD, as long as the soils are properly protected from wet
weather, not placed during periods of precipitation, and that they can be dried if needed to achieve proper
compaction. The contractor should plan to cover and maintain all fill stockpiles with plastic sheeting if it
will be used as structural fill. The reuse of on-site soils is highly dependent on the skill of the contractor and
schedule, and we will work with the design team and contractor to maximize the reuse of on-site till soils
during the wet and dry seasons.
Fill Placement and Compaction Criteria
Structural fill should be mechanically compacted to a firm, non-yielding condition. Structural fill should be
placed in loose lifts not exceeding 12 inches in thickness when using heavy compaction equipment and
not more than 6 inches when using hand-operated compaction equipment. The actual thickness will be
dependent on the structural fill material used and the type and size of compaction equipment. Each lift
should be moisture conditioned to within about 2 percent of the optimum moisture content to achieve
proper compaction to the specified density before placing subsequent lifts. Compaction of all structural fill
at the site should be in accordance with the ASTM D 1557 (modified Proctor) test method. Structural fill
should be compacted to the following criteria:
1. Structural fill placed below floor slabs and foundations should be compacted to 95 percent of the MDD.
2. Structural fill in new pavement and hardscape areas, including utility trench backfill, should be
compacted to at least 90 percent of the MDD, except that the upper 2 feet of fill below final subgrade
should be compacted to at least 95 percent of the MDD, see Figure 3, Compaction Criteria for Trench
Backfill.
3. Structural fill placed as CSBC below pavements should be compacted to 95 percent of the MDD.
4. Non-structural fill, such as fill placed in landscape areas, should be compacted to at least 90 percent
of the MDD.
Weather Considerations
Disturbance of near-surface soils should be expected if earthwork is completed during periods of wet
weather. During dry weather, the soils will: (1) be less susceptible to disturbance, (2) provide better support
for construction equipment, and (3) be more likely to meet the required compaction criteria.
The wet weather season generally begins in October and continues through May in western Washington;
however, periods of wet weather may occur during any month of the year. For earthwork activities during
wet weather, we recommend that the following steps be taken:
■ The ground surface in and around the work area should be sloped so that surface water is directed
away from the work area. The ground surface should be graded so that areas of ponded water do not
develop. Measures should be taken by the contractor to prevent surface water from collecting in
excavations and trenches. Measures should be implemented to remove surface water from the work
area.
■ Earthwork activities should not take place during periods of moderate to heavy precipitation.
■ Slopes with exposed soils should be covered with plastic sheeting.
November 15, 2018 | Page 12 File No. 23656-001-00
■ The contractor should take necessary measures to prevent on-site soils and soils to be used as fill from
becoming wet or unstable. These measures may include the use of plastic sheeting, sumps with pumps,
and grading. The site soils should not be left uncompacted and exposed to moisture. Sealing the
surficial soils by rolling with a smooth-drum roller prior to periods of precipitation will help reduce the
extent that these soils become wet or unstable.
■ The contractor should cover all soil stockpiles that will be used as structural fill with plastic sheeting.
■ Construction traffic should be restricted to specific areas of the site, preferably areas that are surfaced
with the existing asphalt or working pad materials not susceptible to wet weather disturbance.
■ Construction activities should be scheduled so that the length of time that soils are left exposed to
moisture is reduced to the extent practical.
Routing of equipment on the existing fill and native till subgrade soils during the wet weather months will
be difficult and the subgrade will likely become highly disturbed and rutted. In addition, a significant amount
of mud can be produced by routing equipment directly on the glacial soils in wet weather. Therefore, to
protect the subgrade soils and to provide an adequate wet weather working surface for the contractor’s
equipment and labor, we recommend that the contractor protect exposed subgrade soils with sand and
gravel, crushed gravel, or ATB.
Permanent Cut and Fill Slopes
We recommend that permanent cut or fill slopes be constructed at inclinations of 2H:1V or flatter, and be
blended into existing slopes with smooth transitions. To achieve uniform compaction, we recommend that
fill slopes be overbuilt slightly and subsequently cut back to expose well compacted fill. It is our experience
that permanent cut slopes made in dense to very dense glacial till are difficult to establish vegetation on
and difficult to place and maintain topsoil on. Therefore, 3H:1V or flatter permanent cut slopes should be
considered for landscape purposes if site conditions allow for their use.
To reduce erosion, newly constructed slopes should be planted or hydroseeded shortly after completion of
grading. Until the vegetation is established, some sloughing and raveling of the slopes should be expected.
This may necessitate localized repairs and reseeding. Temporary covering, such as clear heavy plastic
sheeting, jute fabric, or erosion control blankets (such as American Excelsior Curlex 1 or North American
Green SC150) could be used to protect the slopes during periods of rainfall.
Utility Trenches
Trench excavation, pipe bedding, and trench backfilling should be completed using the general procedures
described in the 2018 WSDOT Standard Specifications or other suitable procedures specified by the project
civil engineer. The native glacial deposits and fill soils encountered at the site are generally of low corrosivity
based on our experience in the Puget Sound area.
Utility trench backfill should consist of structural fill and should be placed in loose lifts not exceeding
12 inches in thickness when using heavy compaction equipment and not more than 6 inches when using
hand-operated compaction equipment such that adequate compaction can be achieved throughout the lift.
Each lift must be compacted prior to placing the subsequent lift. The backfill should be compacted in
accordance with the criteria discussed above. Figure 3 illustrates recommended trench compaction criteria
under pavement and non-structural areas.
November 15, 2018 | Page 13 File No. 23656-001-00
Sedimentation and Erosion Control
In our opinion, the erosion potential of the on-site soils is low to moderate. Construction activities including
stripping and grading will expose soils to the erosional effects of wind and water. The amount and potential
impacts of erosion are partly related to the time of year that construction actually occurs. Wet weather
construction will increase the amount and extent of erosion and potential sedimentation.
Erosion and sedimentation control measures may be implemented by using a combination of interceptor
swales, straw bale barriers, silt fences and straw mulch for temporary erosion protection of exposed soils.
All disturbed areas should be finish graded and seeded as soon as practicable to reduce the risk of erosion.
Erosion and sedimentation control measures should be installed and maintained in accordance with the
requirements of the City of Renton.
Excavations
We anticipate that excavations are limited and will be primarily associated with footing excavations and
underground utilities. These cuts can likely be made as temporary open cut slopes depending on site
constraints. The stability of open cut slopes is a function of soil type, groundwater seepage, slope
inclination, slope height and nearby surface loads. The use of inadequately designed open cuts could
impact the stability of adjacent work areas, existing utilities, and endanger personnel.
The contractor performing the work has the primary responsibility for protection of workmen and adjacent
improvements. In our opinion, the contractor will be in the best position to observe subsurface conditions
continuously throughout the construction process and to respond to variable soil and groundwater
conditions. Therefore, the contractor should have the primary responsibility for deciding whether or not to
use open cut slopes for much of the excavations rather than some form of temporary excavation support,
and for establishing the safe inclination of the cut slope. Acceptable slope inclinations for utilities and
ancillary excavations should be determined during construction. Because of the diversity of construction
techniques and available shoring systems, the design of temporary shoring is most appropriately left up to
the contractor proposing to complete the installation. Temporary cut slopes and shoring must comply with
the provisions of Title 296 WAC, Part N, “Excavation, Trenching and Shoring.”
The excavations for the buildings and utilities will be completed primarily in loose to medium dense fill and
dense to very dense glacial till deposits. The following sections summarize the general excavation
recommendations.
Temporary Cut Slopes
For planning purposes, temporary unsupported cut slopes more than 4 feet high may be inclined at 1H:1V
maximum steepness within the dense to very dense glacial till (below a depth of about 3 feet) and 1½H:IV
maximum steepness in the overlying fill (upper 3 feet). If significant seepage is present on the cut face then
the cut slopes may have to be flattened. However, temporary cuts should be discussed with the
geotechnical engineer during final design development to evaluate suitable cut slope inclinations for the
various portions of the excavation. The contractor should scale slopes cut at 1H:1V to remove loose
materials and cobbles.
The above guidelines assume that surface loads such as traffic, construction equipment, stockpiles or
building supplies will be kept away from the top of the cut slopes a sufficient distance so that the stability
November 15, 2018 | Page 14 File No. 23656-001-00
of the excavation is not affected. We recommend that this distance be at least 5 feet from the top of the
cut for temporary cuts made at 1H:1V or flatter, and no closer than a distance equal to one-half the height
of the slope for cuts made steeper than 1H:IV.
Water that enters the excavation must be collected and routed away from prepared subgrade areas. We
expect that this may be accomplished by installing a system of drainage ditches and sumps along the toe
of the cut slopes. Some sloughing and raveling of the cut slopes should be expected. Temporary covering,
such as heavy plastic sheeting with appropriate ballast, should be used to protect these slopes during
periods of wet weather. Surface water runoff from above cut slopes should be prevented from flowing over
the slope face by using berms, drainage ditches, swales or other appropriate methods.
If temporary cut slopes experience excessive sloughing or raveling during construction, it may become
necessary to modify the cut slopes to maintain safe working conditions. Slopes experiencing problems can
be flattened, regraded to add intermediate slope benches, or additional dewatering can be provided if the
poor slope performance is related to groundwater seepage.
Drainage Considerations
We anticipate shallow groundwater seepage may enter excavations for utilities depending on the time of
year construction takes place, especially in the winter months. However, we expect that this seepage water
can be handled by digging interceptor trenches in the excavations and pumping from sumps. The seepage
water, if not intercepted and removed from the excavations, will make it difficult to place and compact
structural fill and may destabilize cut slopes.
All paved and landscaped areas should be graded so that surface drainage is directed away from the
buildings to appropriate catch basins.
Water collected in roof downspout lines must not be routed to the footing drain lines. Collected downspout
water should be routed to appropriate discharge points in separate pipe systems.
Infiltration Considerations
Sieve analyses were performed on selected soil samples collected from the test pits that were completed
as part of this study. The soil samples typically consisted of native weathered or relatively unweathered
glacial till. The design infiltration value described below is based on the results of the grain size analyses,
the United States Department of Agriculture (USDA) Textural Triangle, and the Washington State
Department of Ecology Storm Water Management Manual (2005). The grain size analyses are presented
in Appendix B.
Based on our analysis, it is our opinion that the on-site native glacial till soils have a very low infiltration
capacity. The majority of the soils across the site contain significant fines, which limits the infiltration
capacity. The results of the sieve analyses indicated that the fines content (material passing the U.S.
No. 200 sieve) typically ranges from 30 to 35 percent. Due to the density, high fines content, and relative
impermeability of the glacial till, infiltration should be assumed to be very low when designing infiltration
systems. We recommend a preliminary infiltration rate of not more than 0.2 inches per hour be used for
design of the infiltration facilities. Depending on the depth of proposed infiltration facilities, the infiltration
rate will vary; however, we recommend site specific pilot infiltration testing be performed to determine the
design infiltration rate if specific infiltration facilities are being considered.
November 15, 2018 | Page 15 File No. 23656-001-00
RECOMMENDED ADDITIONAL GEOTECHNICAL SERVICES
Throughout this report, recommendations are provided where we consider additional geotechnical services
to be appropriate. These additional services are summarized below:
■ GeoEngineers should be retained to review the project plans and specifications when complete to
confirm that our design recommendations have been implemented as intended.
■ During construction, GeoEngineers should observe and evaluate the suitability of the foundation
subgrades, evaluate the suitability of floor slab and pavement subgrades, observe installation of
subsurface drainage measures including footing drains, observe and test structural backfill, and
provide a summary letter of our construction observation services. The purposes of GeoEngineers
construction phase services are to confirm that the subsurface conditions are consistent with those
observed in the explorations and other reasons described in Appendix D, Report Limitations and
Guidelines for Use.
LIMITATIONS
We have prepared this report for use by Homestead Community Land Trust and members of the project
team for use in design of this project.
Within the limitations of scope, schedule and budget, our services have been executed in accordance with
generally accepted practices in the field of geotechnical engineering in this area at the time this report was
prepared. No warranty or other conditions, express or implied, should be understood.
Please refer to Appendix D for additional information pertaining to use of this report.
REFERENCES
International Code Council, 2015, “International Building Code.”
Mullineaux, D. R., 1965, “Geologic Map of the Renton Quadrangle, King County, Washington.”
Soil & Environmental Engineers, Inc., 2011, “Report of Geotechnical Investigation, Proposed Residential
Development, Edmonds and Glennwood Ave NE, Renton, Washington.”
United States Geological Survey – Earthquake Hazards Program Software, “U.S. Seismic Design Maps,”
2008 data, 2012/2015 IBC, https://earthquake.usgs.gov/designmaps/us/application.php.
Washington State Department of Transportation, 2018, “Standard Specifications for Road, Bridge and
Municipal Construction.”
FIGURES
µ
SITE
Vicinity Map
Figure 1
Willow Crest Townhomes Renton, Washington
2,000 2,0000
Feet
Data Source: Mapbox Open Street Map, 2018
Notes:1. The locations of all features shown are approximate.2. This drawing is for information purposes. It is intended to assist inshowing features discussed in an attached document. GeoEngineers, Inc.cannot guarantee the accuracy and content of electronic files. The masterfile is stored by GeoEngineers, Inc. and will serve as the official record ofthis communication.
Projection: NAD 1983 UTM Zone 10N
P:\23\23656001\GIS\2365600100_F01_VicinityMap.mxd Date Exported: 10/17/18 by cchelf
310315320325 330335340345308309311312313314316317318319321322323324326
3
2
7 328329331332333 3343363373383393413423
4
3
3
4
4 3463053103153203253303353403453453
0
1
3
0
2
3
03 3043063073083093113123133143163173183193213223233243263
2
7
3
2
8
3
2
9 3313323333
3
4 336337338339341342343344345344346343
3443
2
0
325 33033534031
8
31
9 32132
2
32
3
324 3263273283293313323333343343343363373373373
3
8
3393413
4
2 342342
343
295
300
3
0
5
3
1
0
292
293
294296297
298
299
301
302
30
3
30
4
3
0
63073
0
8
3
0
9
31
1
312
3103153203253303353
4
0
3
4
5
3093113123133143163173183193213223233243263
27 328329331332333334336337338
3
3
9
34134234334
4
3
4
6
347
340341342343345343344345346345342343344346 3
4
7
34
7347
3473473463473473
4
7
Edmonds Ave NEGlenwood Ave NEGEI-TP-1
GEI-TP-2
GEI-TP-3
GEI-TP-4
GEI-TP-5
GEI-TP-6
B-1
B-2
TP-1
TP-2
TP-3
TP-4 TP-5
TP-6
Figure 2
Site Plan - Proposed Development
Willow Crest Townhomes Renton,
Washington
W E
N
S
P:\23\23656001\CAD\00\GeoTech\2365600100_F02_Site Plan.dwg TAB:F02 Date Exported: 10/31/18 - 10:19 by hmaraLegendNotes:
1. The locations of all features shown are approximate.
2. This drawing is for information purposes. It is intended to
assist in showing features discussed in an attached document.
GeoEngineers, Inc. cannot guarantee the accuracy and content
of electronic files. The master file is stored by GeoEngineers,
Inc. and will serve as the official record of this communication.
Data Source: Base survey by Lank Tree Land Surveying dated
10/17/18. Proposed site features from Third Place Design
Co-Operative dated 10/7/18.
Projection: WA State Plane, North Zone, NAD83, US Foot Feet
040 40
Test Pit by GeoEngineers, 2018 (Current Study)GEI-TP-1
Boring by Soil & Environmental Engineers, 2011B-1
Test Pit by Soil & Environmental Engineers, 2011TP-1
Site Boundary
4 Unit
Town Homes
4 Unit
Town Homes
4 Unit
Town Homes
Figure 3
P:\23\23656001\CAD\00\GeoTech\2365600100_F03_Compaction Criteria.dwg TAB:F03 Date Exported: 10/19/18 - 13:02 by hmara95
90 90
95
90
Pipe
Varies
Varies
(See Note 1)
2 Feet
Varies
(Modified Proctor)
Pipe Bedding
Trench Backfill
Base Course
Concrete or Asphalt Pavement
Maximum Dry Density, by Test Method ASTM D1557
Recommended Compaction as a Percentage of
Legend
95
Notes:
1. All backfill under building areas should be compacted to at
least 95 percent per ASTM D1557.
Non-structural
Areas
Hardscape Or
Pavement
Areas
Ground Surface
Not To Scale
Compaction Criteria
for Trench Backfill
Willow Crest Townhomes
Renton, Washington
APPENDICES
APPENDIX A
Field Explorations
November 15, 2018 | Page A-1 File No. 23656-001-00
APPENDIX A
FIELD EXPLORATIONS
Subsurface soil and groundwater conditions were evaluated by completing six test pits (GEI-TP-1 through
GEI-TP-6) at the approximate locations shown on Figure 2, Site Plan. Locations of the test pits were
determined in the field by pacing and tape measuring distances from the test pit locations to existing site
features. Ground surface elevations were interpolated from a site topographic map.
Test pits (GEI-TP-1 through GEI-TP-6) were completed on October 22, 2018 at the approximate locations
shown on Figure 2. The test pits were excavated to depths of about 8 feet below the existing ground surface
(bgs). The test pits were completed using a mini rubber track mounted Takeuchi TB138BFR excavator
owned and operated by Kelly’s Excavating.
The test pits were continuously monitored by a geotechnical engineer from our firm who evaluated and
classified the soils encountered, obtained representative soil samples, and observed groundwater
conditions (if present). Our representative maintained a detailed log of each test pit. Disturbed samples of
representative soil types were obtained from the excavator bucket at representative depths.
Soils encountered in the test pits were classified in the field in general accordance with ASTM D 2488, the
Standard Practice for Classification of Soils, Visual-Manual Procedure, which is summarized in Figure A-1.
Logs of the test pits are provided in Figures A-2 through A-7.
Measured groundwater level in exploration,
well, or piezometer
Measured free product in well or piezometer
Distinct contact between soil strata
Approximate contact between soil strata
Contact between geologic units
SYMBOLS TYPICAL
DESCRIPTIONS
GW
GP
SW
SP
SM
FINE
GRAINED
SOILS
SILTS AND
CLAYS
NOTE: Multiple symbols are used to indicate borderline or dual soil classifications
MORE THAN 50%
RETAINED ON
NO. 200 SIEVE
MORE THAN 50%
PASSING
NO. 200 SIEVE
GRAVEL
AND
GRAVELLY
SOILS
SC
LIQUID LIMIT
LESS THAN 50
(APPRECIABLE AMOUNT
OF FINES)
(APPRECIABLE AMOUNT
OF FINES)
COARSE
GRAINED
SOILS
MAJOR DIVISIONS GRAPH LETTER
GM
GC
ML
CL
OL
SILTS AND
CLAYS
SANDS WITH
FINES
SAND
AND
SANDY
SOILS
MH
CH
OH
PT
(LITTLE OR NO FINES)
CLEAN SANDS
GRAVELS WITH
FINES
CLEAN GRAVELS
(LITTLE OR NO FINES)
WELL-GRADED GRAVELS, GRAVEL -SAND MIXTURES
CLAYEY GRAVELS, GRAVEL - SAND -CLAY MIXTURES
WELL-GRADED SANDS, GRAVELLYSANDS
POORLY-GRADED SANDS, GRAVELLYSAND
SILTY SANDS, SAND - SILT MIXTURES
CLAYEY SANDS, SAND - CLAYMIXTURES
INORGANIC SILTS, ROCK FLOUR,CLAYEY SILTS WITH SLIGHTPLASTICITY
INORGANIC CLAYS OF LOW TOMEDIUM PLASTICITY, GRAVELLYCLAYS, SANDY CLAYS, SILTY CLAYS,LEAN CLAYS
ORGANIC SILTS AND ORGANIC SILTYCLAYS OF LOW PLASTICITY
INORGANIC SILTS, MICACEOUS ORDIATOMACEOUS SILTY SOILS
INORGANIC CLAYS OF HIGHPLASTICITY
ORGANIC CLAYS AND SILTS OFMEDIUM TO HIGH PLASTICITY
PEAT, HUMUS, SWAMP SOILS WITHHIGH ORGANIC CONTENTSHIGHLY ORGANIC SOILS
SOIL CLASSIFICATION CHART
MORE THAN 50%
OF COARSE
FRACTION RETAINED
ON NO. 4 SIEVE
MORE THAN 50%
OF COARSE
FRACTION PASSING
ON NO. 4 SIEVE
SILTY GRAVELS, GRAVEL - SAND -SILT MIXTURES
POORLY-GRADED GRAVELS,GRAVEL - SAND MIXTURES
LIQUID LIMIT GREATER
THAN 50
Continuous Coring
Bulk or grab
Direct-Push
Piston
Shelby tube
Standard Penetration Test (SPT)
2.4-inch I.D. split barrel
Contact between soil of the same geologic
unit
Material Description Contact
Graphic Log Contact
NOTE: The reader must refer to the discussion in the report text and the logs of explorations for a proper understanding of subsurface conditions.
Descriptions on the logs apply only at the specific exploration locations and at the time the explorations were made; they are not warranted to be
representative of subsurface conditions at other locations or times.
Groundwater Contact
Blow count is recorded for driven samplers as the number of
blows required to advance sampler 12 inches (or distance noted).
See exploration log for hammer weight and drop.
"P" indicates sampler pushed using the weight of the drill rig.
"WOH" indicates sampler pushed using the weight of the
hammer.
Key to Exploration Logs
Figure A-1
Sampler Symbol Descriptions
ADDITIONAL MATERIAL SYMBOLS
NS
SS
MS
HS
No Visible Sheen
Slight Sheen
Moderate Sheen
Heavy Sheen
Sheen Classification
SYMBOLS
Asphalt Concrete
Cement Concrete
Crushed Rock/
Quarry Spalls
Topsoil
GRAPH LETTER
AC
CC
SOD Sod/Forest Duff
CR
DESCRIPTIONS
TYPICAL
TS
Laboratory / Field Tests
%F
%G
AL
CA
CP
CS
DD
DS
HA
MC
MD
Mohs
OC
PM
PI
PP
SA
TX
UC
VS
Percent fines
Percent gravel
Atterberg limits
Chemical analysis
Laboratory compaction test
Consolidation test
Dry density
Direct shear
Hydrometer analysis
Moisture content
Moisture content and dry density
Mohs hardness scale
Organic content
Permeability or hydraulic conductivity
Plasticity index
Pocket penetrometer
Sieve analysis
Triaxial compression
Unconfined compression
Vane shear
Blackberry brambles
Dark brown fine to medium sand with silt, occasional gravel, roots
(loose, moist) (fill)
Light brown silty fine to medium sand with gravel, occasional cobbles,
trace roots (medium dense, moist) (weathered glacial till)
Gray silty fine to medium sand with gravel (very dense, moist) (glacial
till)
WD
SP-SM
SM
SM
1
SA
2
%F
3
4
4
3
Pocket Pen / Probe Penetration
0.0 kg/cm2 / 6 inches
0.5 kg/cm2 / 4 inches
>4.5 kg/cm2 / ½ inch
>4.5 kg/cm2 / <½ inch
21
30
Notes: See Figure A-1 for explanation of symbols.
The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.
Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth.Date:11/5/18 Path:W:\PROJECTS\23\23656001\GINT\2365600100.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number:
Project Location:
Project:
Renton, Washington
23656-001-00
Log of Test Pit GEI-TP-1
Willow Crest Townhomes
Figure A-2Elevation (feet)339338337336335334333332Depth (feet)1
2
3
4
5
6
7
8 Testing SampleGraphic LogSAMPLE
MATERIAL
DESCRIPTION
GroupClassificationSample NameTestingMoistureContent (%)REMARKS
FinesContent (%)Date
Excavated
Surface Elevation (ft)
Vertical Datum
Coordinate System
Horizontal Datum
Easting (X)
Northing (Y)
Total
Depth (ft)10/22/2018 8
340
NAVD88
1306462
186084
WA State Plane North
NAD83 (feet)
AJF
Checked By MAG
Groundwater not observed
Caving not observedEquipment Takeuchi TB138FR
Logged By Excavator Kelly's Excavating, Inc.
Blackberry brambles
Dark brown fine to medium sand with silt, roots (loose, moist) (fill)
Brown silty coarse gravel with sand and occasional cobbles, roots
(medium dense to dense, moist) (weathered glacial till)
No roots below 2 feet
Gray silty fine sand with occasional gravel and cobbles (very dense,
moist) (glacial till)
WD
SP-SM
GM
SM
1
SA
2
3
4
3
Pocket Pen / Probe Penetration
0.0 kg/cm2 / 8 inches
1.0 kg/cm2 / 3 inches
>4.5 kg/cm2 / 1 inch
>4.5 kg/cm2 / ¼ inch
17
Notes: See Figure A-1 for explanation of symbols.
The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.
Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth.Date:11/5/18 Path:W:\PROJECTS\23\23656001\GINT\2365600100.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number:
Project Location:
Project:
Renton, Washington
23656-001-00
Log of Test Pit TEI-TP-2
Willow Crest Townhomes
Figure A-3Elevation (feet)339338337336335334333332Depth (feet)1
2
3
4
5
6
7
8 Testing SampleGraphic LogSAMPLE
MATERIAL
DESCRIPTION
GroupClassificationSample NameTestingMoistureContent (%)REMARKS
FinesContent (%)Date
Excavated
Surface Elevation (ft)
Vertical Datum
Coordinate System
Horizontal Datum
Easting (X)
Northing (Y)
Total
Depth (ft)10/22/2018 8
340
NAVD88
1306453
186046
WA State Plane North
NAD83 (feet)
AJF
Checked By MAG
Groundwater not observed
Caving not observedEquipment Takeuchi TB138FR
Logged By Excavator Kelly's Excavating, Inc.
Blackberry brambles
Dark brown fine to medium sand with silt and occasional gravel, roots
(loose, moist) (fill)
Light brown silty fine sand with gravel and occasional cobbles, roots
(loose to medium dense, moist) (weathered glacial till)
No roots below 2 feet
Light gray silty fine to medium sand with occasional gravel and cobbles
(very dense, moist) (glacial till)
Gray fine to medium sand with silt, gravel and occasional cobbles (very
dense, moist)
WD
SP-SM
SM
SM
SP-SM
1
SA
2
3
4
5
Pocket Pen / Probe Penetration
0.0 kg/cm2 / 12 inches
2.0 kg/cm2 / 3 inches
>4.5 kg/cm2 / ½ inch
>4.5 kg/cm2 / ¼ inch
32
Notes: See Figure A-1 for explanation of symbols.
The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.
Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth.Date:11/5/18 Path:W:\PROJECTS\23\23656001\GINT\2365600100.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number:
Project Location:
Project:
Renton, Washington
23656-001-00
Log of Test Pit GEI-TP-3
Willow Crest Townhomes
Figure A-4Elevation (feet)339338337336335334333332Depth (feet)1
2
3
4
5
6
7
8 Testing SampleGraphic LogSAMPLE
MATERIAL
DESCRIPTION
GroupClassificationSample NameTestingMoistureContent (%)REMARKS
FinesContent (%)Date
Excavated
Surface Elevation (ft)
Vertical Datum
Coordinate System
Horizontal Datum
Easting (X)
Northing (Y)
Total
Depth (ft)10/22/2018 8
340
NAVD88
1306422
185979
WA State Plane North
NAD83 (feet)
AJF
Checked By MAG
Groundwater not observed
Caving not observedEquipment Takeuchi TB138FR
Logged By Excavator Kelly's Excavating, Inc.
Blackberry brambles
Dark brown fine to medium sand with silt and occasional gravel, roots
(loose, moist) (fill)
Light brown silty fine sand with gravel and occasional cobbles (loose to
medium dense, moist) (weathered glacial till)
Light gray silty fine to medium sand with gravel and occasional
cobbles; partially cemented (very dense, moist) (glacial till)
Boulder encountered at 3½ feet
WD
SP-SM
SM
SM
1
2
SA
3
4
6
Pocket Pen / Probe Penetration
0.0 kg/cm2 / 12 inches
2.25 kg/cm2 / 4 inches
>4.5 kg/cm2 / 1 inch
>4.5 kg/cm2 / ¼ inch
35
Notes: See Figure A-1 for explanation of symbols.
The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.
Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth.Date:11/5/18 Path:W:\PROJECTS\23\23656001\GINT\2365600100.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number:
Project Location:
Project:
Renton, Washington
23656-001-00
Log of Test Pit GEI-TP-4
Willow Crest Townhomes
Figure A-5Elevation (feet)339338337336335334333332Depth (feet)1
2
3
4
5
6
7
8 Testing SampleGraphic LogSAMPLE
MATERIAL
DESCRIPTION
GroupClassificationSample NameTestingMoistureContent (%)REMARKS
FinesContent (%)Date
Excavated
Surface Elevation (ft)
Vertical Datum
Coordinate System
Horizontal Datum
Easting (X)
Northing (Y)
Total
Depth (ft)10/22/2018 8
340
NAVD88
1306466
185974
WA State Plane North
NAD83 (feet)
AJF
Checked By MAG
Groundwater not observed
Caving not observedEquipment Takeuchi TB138FR
Logged By Excavator Kelly's Excavating, Inc.
Blackberry brambles
Brown fine to medium sand with silt and occasional gravel (loose,
moist) (fill)
Light brown silty fine sand with gravel and cobbles, roots (loose to
medium dense, moist) (weathered glacial till)
Gray silty fine sand with gravel and occasional cobbles; partially
cemented (dense to very dense, moist) (glacial till)
WD
SP-SM
SM
SM
1
%F
2
3
4
8
Pocket Pen / Probe Penetration
0.0 kg/cm2 / 12 inches
1.5 kg/cm2 / 5 inches
2.5 kg/cm2 / 2 inches
>4.5 kg/cm2 / ¼ inch
26
Notes: See Figure A-1 for explanation of symbols.
The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.
Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth.Date:11/5/18 Path:W:\PROJECTS\23\23656001\GINT\2365600100.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number:
Project Location:
Project:
Renton, Washington
23656-001-00
Log of Test Pit GEI-TP-5
Willow Crest Townhomes
Figure A-6Elevation (feet)339338337336335334333332Depth (feet)1
2
3
4
5
6
7
8 Testing SampleGraphic LogSAMPLE
MATERIAL
DESCRIPTION
GroupClassificationSample NameTestingMoistureContent (%)REMARKS
FinesContent (%)Date
Excavated
Surface Elevation (ft)
Vertical Datum
Coordinate System
Horizontal Datum
Easting (X)
Northing (Y)
Total
Depth (ft)10/22/2018 8
340
NAVD88
1306422
185911
WA State Plane North
NAD83 (feet)
AJF
Checked By MAG
Groundwater not observed
Caving not observedEquipment Takeuchi TB138FR
Logged By Excavator Kelly's Excavating, Inc.
Blackberry brambles
Brown fine to medium sand with silt and occasional gravel (loose,
moist) (fill)
Light brown silty fine to medium sand with gravel and cobbles, roots
(loose to medium dense, moist) (weathered till)
Gray silty fine to medium sand with gravel and occasional cobbles
(dense to very dense, moist) (glacial till)
WD
SP-SM
SM
SM
1
2
SA
3
4
5
Pocket Pen / Probe Penetration
0.0 kg/cm2 / 12 inches
1.5 kg/cm2 / 5 inches
4.0 kg/cm2 / 1½ inches
>4.5 kg/cm2 / ¼ inch
33
Notes: See Figure A-1 for explanation of symbols.
The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to ½ foot.
Coordinates Data Source: Horizontal approximated based on Aerial Imagery. Vertical approximated based on Google Earth.Date:11/5/18 Path:W:\PROJECTS\23\23656001\GINT\2365600100.GPJ DBLibrary/Library:GEOENGINEERS_DF_STD_US_JUNE_2017.GLB/GEI8_TESTPIT_1P_GEOTEC_%FSheet 1 of 1Project Number:
Project Location:
Project:
Renton, Washington
23656-001-00
Log of Test Pit GEI-TP-6
Willow Crest Townhomes
Figure A-7Elevation (feet)339338337336335334333332Depth (feet)1
2
3
4
5
6
7
8 Testing SampleGraphic LogSAMPLE
MATERIAL
DESCRIPTION
GroupClassificationSample NameTestingMoistureContent (%)REMARKS
FinesContent (%)Date
Excavated
Surface Elevation (ft)
Vertical Datum
Coordinate System
Horizontal Datum
Easting (X)
Northing (Y)
Total
Depth (ft)10/22/2018 8
340
NAVD88
1306474
185878
WA State Plane North
NAD83 (feet)
AJF
Checked By MAG
Groundwater not observed
Caving not observedEquipment Takeuchi TB138FR
Logged By Excavator Kelly's Excavating, Inc.
APPENDIX B
Laboratory Testing
November 15, 2018 | Page B-1 File No. 23656-001-00
APPENDIX B
LABORATORY TESTING
Soil samples obtained from the test pits were transported to our laboratory and examined to confirm or
modify field classifications, as well as to evaluate engineering properties of the soil. Representative
samples were selected for laboratory testing consisting of moisture content, percent fines (material passing
the U.S. No. 200 sieve), grain size determinations (sieve analysis), and modified Proctor testing. The tests
were performed in general accordance with test methods of the ASTM International (ASTM) or other
applicable procedures.
Soil Classifications
Soil samples obtained from the test pits were visually classified in the field and/or in our laboratory using
a system based on the Unified Soil Classification System (USCS) and ASTM classification methods. ASTM
test method D 2488 was used to visually classify the soil samples, while ASTM D 2487 was used to classify
the soils based on laboratory tests results. These classification procedures are incorporated in the test pit
logs shown in Figures A-2 through A-7 in Appendix A.
Moisture Content Determinations
Moisture contents tests were completed in general accordance with ASTM D 2216 for representative
samples obtained from the test pits. The test results are presented on the test pit logs in Appendix A at the
respective sample depth.
Percent Fines Tests
Tests to evaluate the percent fines (particles passing the No. 200 sieve) were completed using
ASTM D 1140. The wet sieve method was used to determine the percentage of soil particles larger than
the U.S. No. 200 sieve opening. The results of the percent fines tests are presented on the test pit logs at
the depths at which the samples were obtained.
Sieve Analysis
Sieve analyses were performed on selected samples in general accordance with ASTM D 422. The wet
sieve analysis method was used to estimate the percentage of soil greater than the U.S. No. 200 mesh
sieve. The results of the sieve analyses were plotted, classified in general accordance with the USCS, and
presented on Figures B-1 and B-2.
Modified Proctor
The modified Proctor tests were completed in general accordance with ASTM D1557. The results of the
modified Proctor testing are presented on Figure B-3.
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.11101001000PERCENT PASSING BY WEIGHT GRAIN SIZE IN MILLIMETERS
U.S. STANDARD SIEVE SIZE
SAND SILT OR CLAYCOBBLES
GRAVEL
COARSE MEDIUM FINECOARSEFINE
Boring Number
Depth
(feet)Soil Description
TP-1
TP-2
TP-3
TP-4
2
2
1.5
4
Silty fine to medium sand with gravel (SM)
Silty coarse gravel with sand (GM)
Silty fine sand with gravel (SM)
Silty fine to medium sand with gravel (SM)
Symbol
Moisture
(%)
4
3
5
6
3/8”3”1.5”#4 #10 #20 #40 #60 #1003/4”Figure B-1Sieve Analysis ResultsWillow Crest Townhomes Renton, Washington23656-001-00 Date Exported: 10/31/18
Note:This report may not be reproduced,except in full,without written approval of GeoEngineers,Inc.Test results are applicable only to the specific sample on which they were
performed,and should not be interpreted as representative of any other samples obtained at other times,depths or locations,or generated by separate operations or processes.
The grain size analysis results were obtained in general accordance with ASTM D 6913.GeoEngineers 17425 NE Union Hill Road Ste 250,Redmond,WA 98052
#200
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.11101001000PERCENT PASSING BY WEIGHT GRAIN SIZE IN MILLIMETERS
U.S. STANDARD SIEVE SIZE
SAND SILT OR CLAYCOBBLES
GRAVEL
COARSE MEDIUM FINECOARSEFINE
Boring Number
Depth
(feet)Soil Description
TP-6 4 Silty fine to medium sand with gravel (SM)
Symbol
Moisture
(%)
5
3/8”3”1.5”#4 #10 #20 #40 #60 #1003/4”Figure B-2Sieve Analysis ResultsWillow Crest Townhomes Renton, Washington23656-001-00 Date Exported: 10/31/18
Note:This report may not be reproduced,except in full,without written approval of GeoEngineers,Inc.Test results are applicable only to the specific sample on which they were
performed,and should not be interpreted as representative of any other samples obtained at other times,depths or locations,or generated by separate operations or processes.
The grain size analysis results were obtained in general accordance with ASTM D 6913.GeoEngineers 17425 NE Union Hill Road Ste 250,Redmond,WA 98052
#200
Figure B-3
Compaction Test Results (TP-3)
Willow Crest Townhomes
Renton, Washington
23656-001-00 Date Exported: 10/30/18Note:This report may not be reproduced,except in full,without written approval
of GeoEngineers,Inc.Test results are applicable only to the specific
sample on which they were performed,and should not be interpreted as
representative of any other samples obtained at other times,depths or
locations,or generated by separate operations or processes.
The Proctor results were obtained in general accordance with
ASTM D 1557.
Boring
Number Soil Description
Optimum
Moisture
(%)
Maximum
Dry Density
(pcf)
Uncorrected TP-3 Silty fine sand with gravel (SM)11.8 120.0
Symbol
100
105
110
115
120
125
130
135
140
0 5 10 15 20
MOISTURE CONTENT (%)DRY DENSITY (pcf)100%
Saturation
(Gs=2.65)
Depth
(feet)
1.5
APPENDIX C
Boring and Test Pit Logs from Previous Studies
November 15, 2018 | Page C-1 File No. 23656-001-00
APPENDIX C
BORING AND TEST PIT LOGS FROM PREVIOUS STUDIES
Included in Appendix C are the boring and test pit logs from available previous studies completed in the
immediate vicinity of the project site.
■ The logs of two borings (B-1 and B-2) and six test pits (TP-1 through TP-6) completed by Soil and
Environmental Engineers, Inc., in 2010 for the Proposed Development at Edmonds Avenue NE and
Glennwood Avenue NE project.
APPENDIX D
Report Limitations and Guidelines for Use
November 15, 2018 | Page D-1
File No. 23656-001-00
APPENDIX D
REPORT LIMITATIONS AND GUIDELINES FOR USE 1
This appendix provides information to help you manage your risks with respect to the use of this report.
Geotechnical Services Are Performed for Specific Purposes, Persons and Projects
This report has been prepared for the exclusive use of Homestead Community Land Trust and other
project team members for the Willow Crest Townhomes project. This report is not intended for use by
others, and the information contained herein is not applicable to other sites.
GeoEngineers structures our services to meet the specific needs of our clients. For example, a geotechnical
or geologic study conducted for a civil engineer or architect may not fulfill the needs of a construction
contractor or even another civil engineer or architect that are involved in the same project. Because each
geotechnical or geologic study is unique, each geotechnical engineering or geologic report is unique,
prepared solely for the specific client and project site. Our report is prepared for the exclusive use of our
Client. No other party may rely on the product of our services unless we agree in advance to such reliance
in writing. This is to provide our firm with reasonable protection against open-ended liability claims by third
parties with whom there would otherwise be no contractual limits to their actions. Within the limitations of
scope, schedule and budget, our services have been executed in accordance with our Agreement with the
Client and generally accepted geotechnical practices in this area at the time this report was prepared. This
report should not be applied for any purpose or project except the one originally contemplated.
A Geotechnical Engineering or Geologic Report Is Based on a Unique Set of Project-specific
Factors
This report has been prepared for the Willow Crest Townhomes project in Renton, Washington.
GeoEngineers considered a number of unique, project-specific factors when establishing the scope of
services for this project and report. Unless GeoEngineers specifically indicates otherwise, do not rely on
this report if it was:
■not prepared for you,
■not prepared for your project,
■not prepared for the specific site explored, or
■completed before important project changes were made.
For example, changes that can affect the applicability of this report include those that affect:
■the function of the proposed structure;
■elevation, configuration, location, orientation or weight of the proposed structure;
1 Developed based on material provided by ASFE, Professional Firms Practicing in the Geosciences; www.asfe.org .
November 15, 2018 | Page D-2 File No. 23656-001-00
■ composition of the design team; or
■ project ownership.
If important changes are made after the date of this report, GeoEngineers should be given the opportunity
to review our interpretations and recommendations and provide written modifications or confirmation, as
appropriate.
Subsurface Conditions Can Change
This geotechnical or geologic report is based on conditions that existed at the time the study was performed.
The findings and conclusions of this report may be affected by the passage of time, by manmade events
such as construction on or adjacent to the site, or by natural events such as floods, earthquakes, slope
instability or groundwater fluctuations. Always contact GeoEngineers before applying a report to determine
if it remains applicable.
Most Geotechnical and Geologic Findings Are Professional Opinions
Our interpretations of subsurface conditions are based on field observations from widely spaced sampling
locations at the site. Site exploration identifies subsurface conditions only at those points where subsurface
tests are conducted or samples are taken. GeoEngineers reviewed field and laboratory data and then
applied our professional judgment to render an opinion about subsurface conditions throughout the site.
Actual subsurface conditions may differ, sometimes significantly, from those indicated in this report. Our
report, conclusions and interpretations should not be construed as a warranty of the subsurface conditions.
Geotechnical Engineering Report Recommendations Are Not Final
Do not over-rely on the preliminary construction recommendations included in this report. These
recommendations are not final, because they were developed principally from GeoEngineers’ professional
judgment and opinion. GeoEngineers’ recommendations can be finalized only by observing actual
subsurface conditions revealed during construction. GeoEngineers cannot assume responsibility or liability
for this report's recommendations if we do not perform construction observation.
Sufficient monitoring, testing and consultation by GeoEngineers should be provided during construction to
confirm that the conditions encountered are consistent with those indicated by the explorations, to provide
recommendations for design changes should the conditions revealed during the work differ from those
anticipated, and to evaluate whether or not earthwork activities are completed in accordance with our
recommendations. Retaining GeoEngineers for construction observation for this project is the most
effective method of managing the risks associated with unanticipated conditions.
A Geotechnical Engineering or Geologic Report Could Be Subject to Misinterpretation
Misinterpretation of this report by other design team members can result in costly problems. You could
lower that risk by having GeoEngineers confer with appropriate members of the design team after
submitting the report. Also retain GeoEngineers to review pertinent elements of the design team's plans
and specifications. Contractors can also misinterpret a geotechnical engineering or geologic report. Reduce
that risk by having GeoEngineers participate in pre-bid and preconstruction conferences, and by providing
construction observation.
November 15, 2018 | Page D-3 File No. 23656-001-00
Do Not Redraw the Exploration Logs
Geotechnical engineers and geologists prepare final boring and testing logs based upon their interpretation
of field logs and laboratory data. To prevent errors or omissions, the logs included in a geotechnical
engineering or geologic report should never be redrawn for inclusion in architectural or other design
drawings. Only photographic or electronic reproduction is acceptable, but recognize that separating logs
from the report can elevate risk.
Give Contractors a Complete Report and Guidance
Some owners and design professionals believe they can make contractors liable for unanticipated
subsurface conditions by limiting what they provide for bid preparation. To help prevent costly problems,
give contractors the complete geotechnical engineering or geologic report, but preface it with a clearly
written letter of transmittal. In that letter, advise contractors that the report was not prepared for purposes
of bid development and that the report's accuracy is limited; encourage them to confer with GeoEngineers
and/or to conduct additional study to obtain the specific types of information they need or prefer. A pre-bid
conference can also be valuable. Be sure contractors have sufficient time to perform additional study. Only
then might an owner be in a position to give contractors the best information available, while requiring them
to at least share the financial responsibilities stemming from unanticipated conditions. Further, a
contingency for unanticipated conditions should be included in your project budget and schedule.
Contractors Are Responsible for Site Safety on Their Own Construction Projects
Our geotechnical recommendations are not intended to direct the contractor’s procedures, methods,
schedule or management of the work site. The contractor is solely responsible for job site safety and for
managing construction operations to minimize risks to on-site personnel and to adjacent properties.
Read These Provisions Closely
Some clients, design professionals and contractors may not recognize that the geoscience practices
(geotechnical engineering or geology) are far less exact than other engineering and natural science
disciplines. This lack of understanding can create unrealistic expectations that could lead to
disappointments, claims and disputes. GeoEngineers includes these explanatory “limitations” provisions in
our reports to help reduce such risks. Please confer with GeoEngineers if you are unclear how these “Report
Limitations and Guidelines for Use” apply to your project or site.
Geotechnical, Geologic and Environmental Reports Should Not Be Interchanged
The equipment, techniques and personnel used to perform an environmental study differ significantly from
those used to perform a geotechnical or geologic study and vice versa. For that reason, a geotechnical
engineering or geologic report does not usually relate any environmental findings, conclusions or
recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated
contaminants. Similarly, environmental reports are not used to address geotechnical or geologic concerns
regarding a specific project.
November 15, 2018 | Page D-4 File No. 23656-001-00
Biological Pollutants
GeoEngineers’ Scope of Work specifically excludes the investigation, detection, prevention or assessment
of the presence of Biological Pollutants. Accordingly, this report does not include any interpretations,
recommendations, findings, or conclusions regarding the detecting, assessing, preventing or abating of
Biological Pollutants and no conclusions or inferences should be drawn regarding Biological Pollutants, as
they may relate to this project. The term “Biological Pollutants” includes, but is not limited to, molds, fungi,
spores, bacteria, and viruses, and/or any of their byproducts.
If Client desires these specialized services, they should be obtained from a consultant who offers services
in this specialized field.