HomeMy WebLinkAboutRS_Geotechnical Report_170929_v1Cobalt
Geosciences
Limited Geotechnical Investigation
Proposed Residential Subdivision
532 Edmonds Avenue NE
Renton, Washington
March 13, 2017
LIMITED GEOTECHNICAL INVESTIGATION
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Table of Contents
1.0 INTRODUCTION ............................................................................................................. 1
2.0 PROJECT DESCRIPTION .............................................................................................. 1
3.0 SITE DESCRIPTION ....................................................................................................... 1
4.0 FIELD INVESTIGATION ............................................................................................... 2
4.1.1 Site Investigation Program ................................................................................... 2
5.0 SOIL AND GROUNDWATER CONDITIONS .............................................................. 2
5.1.1 Area Geology ........................................................................................................ 2
5.1.2 Groundwater ........................................................................................................ 3
6.0 GEOLOGIC HAZARDS ................................................................................................... 3
6.1 Erosion Hazard .............................................................................................................. 3
6.2 Seismic Hazard .................................................................................................... 3
7.0 DISCUSSION ................................................................................................................... 4
7.1.1 General................................................................................................................. 4
8.0 RECOMMENDATIONS .................................................................................................. 5
8.1.1 Site Preparation ................................................................................................... 5
8.1.2 Temporary Excavations ........................................................................................ 5
8.1.3 Erosion and Sediment Control.............................................................................. 6
8.1.4 Foundation Design ............................................................................................... 6
8.1.5 Infiltration Recommendations ............................................................................. 7
8.1.6 Slab-on-Grade ...................................................................................................... 8
8.1.7 Utilities ................................................................................................................ 8
8.1.8 Groundwater Influence on Construction .............................................................. 9
9.0 CONSTRUCTION FIELD REVIEWS ...........................................................................10
10.0 CLOSURE ...................................................................................................................11
LIST OF APPENDICES
Appendix A — Statement of General Conditions
Appendix B — Figures
Appendix C — Test Pit Logs
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P.O. Box 82243, Kenmore, WA 98028
1.0 Introduction
In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a limited
geotechnical investigation for the proposed 2-lot residential subdivision located at 532 Edmonds Avenue
NE in Renton, Washington (Figure 1).
The purpose of the geotechnical investigation was to identify subsurface conditions and to provide
preliminary geotechnical recommendations for foundation design, earthwork, soil compaction, utilities,
general pavement guidelines, and suitability of the on-site soils for use as fill.
The scope of work for the geotechnical investigation consisted of a site investigation followed by
engineering analyses to prepare this report. Recommendations presented herein pertain to various
geotechnical aspects of the proposed development, including foundation design, drainage, and earthwork.
2.0 Project Description
The project includes subdividing the tax parcel into two building lots, presumably followed by
development of the east lot with a new single family residence. The west lot will likely remain developed
with a single family residence (current development).
We anticipate that stormwater runoff will be directed into one or more infiltration drywells or trenches.
The location and depth of any system is unknown at this time.
We anticipate that foundation loads will be generally light and that site grading will include cuts and fills
on the order of 3 feet or less for foundation placement and driveway construction.
3.0 Site Description
The site is located at 532 Edmonds Avenue NE in Renton, Washington (Figure 1). The property consists
of one rectangular parcel (No. 7126300050) with a total area of 16,044 square feet.
The property is currently developed with a single family residence and asphalt driveway. The site is
vegetated with grasses, bushes, and sparse evergreen and deciduous trees.
The property slopes gently downward toward the west at variable magnitudes. The topographic relief
across the property is about 20 feet. There is a masonry retaining wall located in the central portion of the
site (east side of carport) and we understand that the new residence will be located at least 10 feet east of
this wall.
The site is bordered to the north by NE 5th Place, to the west by Edmonds Avenue East, and to the east and
south by single family residences.
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4.0 Field Investigation
4.1.1 Site Investigation Program
The geotechnical field investigation program was completed on February 9, 2017 and included excavating
and sampling two test pits within the property, where accessible.
The soils encountered were logged in the field and are described in accordance with the Unified Soil
Classification System (USCS).
A Cobalt Geosciences field representative conducted the explorations, classified the encountered soils,
kept a detailed log of each test pit, and observed and recorded pertinent site features.
The results of the test pit explorations are presented in Appendix C.
5.0 Soil and Groundwater Conditions
5.1.1 Area Geology
The site lies within the Puget Lowland. The lowland is part of a regional north-south trending trough that
extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington,
this lowland is glacially carved, with a depositional and erosional history including at least four separate
glacial advances/retreats. The Puget Lowland is bounded to the west by the Olympic Mountains and to
the east by the Cascade Range. The lowland is filled with glacial and non-glacial sediments consisting of
interbedded gravel, sand, silt, till, and peat lenses.
The Composite Geologic Map of King County, indicates that the site is located near the contacts of Vashon
Glacial Till and Vashon Recessional Outwash.
Vashon Recessional Outwash consists of normally consolidated sand and gravel with variable amounts of
silt deposited during the most recent glacial retreat. These deposits are commonly underlain by Vashon
Glacial Till.
Vashon Glacial Till is typically characterized by an unsorted, non-stratified mixture of clay, silt, sand,
gravel, cobbles and boulders in variable quantities. These materials are typically dense and relatively
impermeable. The poor sorting reflects the mixing of the materials as these sediments were overridden
and incorporated by the glacial ice.
Test Pit TP-1
Test Pit TP-1 encountered approximately 8 inches of topsoil and vegetation underlain by approximately
2.5 feet of loose, silty-fine to medium grained sand. This layer was underlain by approximately 3 feet of
loose to medium dense, fine to medium grained sand with gravel and trace silt (Recessional Outwash).
This layer was underlain by medium dense, fine to medium grained sand with local pieces of cemented
silty-sand which continued to the termination depth of the test pit. Fine roots extended to about 3 feet
below existing grade in this test pit and soil mottling was observed below about 5 feet.
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Test Pits TP-2
Test Pits TP-2 encountered approximately 6 inches of topsoil and vegetation underlain by approximately
2 feet of loose, silty-fine to medium grained sand. This layer was underlain by loose to medium dense,
fine to medium grained sand with gravel and trace silt (Recessional Outwash), which continued to the
termination depth of the test pit.
Overall Soil Conditions
Based on the explorations conducted, the site is underlain by variable thicknesses of recessional outwash
sands underlain by dense to very dense glacial till. The outwash appears to be at least 8 feet thick within
the property; however, glacial till may be encountered at shallower depths locally.
5.1.2 Groundwater
At the time of our investigation, groundwater was not encountered in either test pit. We anticipate that
light amounts of perched groundwater may develop during the wet season between the recessional
outwash, fill, or weathered glacial till and the underlying unweathered glacial till. Soil mottling was
observed in TP-2 about 5 feet below grade.
Water table elevations often fluctuate over time. The groundwater level will depend on a variety of factors
that may include seasonal precipitation, irrigation, land use, climatic conditions and soil permeability.
Water levels at the time of the field investigation may be different from those encountered during the
construction phase of the project.
6.0 Geologic Hazards
6.1 Erosion Hazard
The Natural Resources Conservation Services (NRCS) maps for King County indicate that the site is
underlain by Indianola Loamy Sand. These soils have a “Moderate” to “Severe” erosion potential in a
disturbed state.
It is our opinion that soil erosion potential at this project site can be reduced through landscaping and
surface water runoff control. Typically erosion of exposed soils will be most noticeable during periods of
rainfall and may be controlled by the use of normal temporary erosion control measures, such as silt
fences, hay bales, mulching, control ditches and diversion trenches. The typical wet weather season, with
regard to site grading, is from October 31st to April 1st. Erosion control measures should be in place before
the onset of wet weather.
6.2 Seismic Hazard
The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the 2015
International Building Code (2015 IBC). A Site Class D applies to an overall profile consisting of medium
dense to very dense soils within the upper 100 feet.
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We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values
for SS, S1, Fa, and Fv. The USGS website includes the most updated published data on seismic conditions.
The site specific seismic design parameters and adjusted maximum spectral response acceleration
parameters are as follows:
PGA (Peak Ground Acceleration, in percent of g)
SS 142.5% of g
S1 53.40% of g
FA 1.00
FV 1.50
Additional seismic considerations include liquefaction potential and amplification of ground motions by
soft/loose soil deposits. The liquefaction potential is highest for loose sand with a high groundwater table.
The relatively dense soil deposits that underlie the site have a relatively low potential for liquefaction. We
do recommend recompaction of loose to medium dense sands below all footing elements prior to
foundation placement.
7.0 DISCUSSION
7.1.1 General
It is our opinion that a future single family residence may be supported on a shallow foundation system
bearing on medium dense or firmer native soils, re-compacted native soils, or on structural fill placed on
native soils per the recommendations in Section 8.1.1 and 8.1.4 of this report.
The near surface soils include loose to medium dense sand with gravel, medium dense silty-sand with
gravel which will require re-compaction per section 8.1.1 and 8.1.4 prior to foundation placement. We
recommend that a qualified geotechnical engineer or geologist monitor footing excavation work and
provide area-specific recommendations for footing subgrade preparation.
All excavations within the building footprint should be backfilled and compacted according to the
recommendations in this report. Any filled areas beneath foundation elements should extend a lateral
distance equal to the depth of the overexcavation in all directions from the faces of the footings. Soils
below foundation elements should be compacted to at least 95 percent of the modified proctor or consist
of medium dense or firmer native soils.
Infiltration of stormwater utilizing drywells or trenches is feasible. However, we recommend that any
system be placed in the east or south portions of the new building lot. Systems should not be located
within 25 feet of the masonry carport wall.
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8.0 Recommendations
8.1.1 Site Preparation
Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic-rich soil.
Based on observations from the site investigation program, it is anticipated that the stripping depth will
range from 6 to 12 inches. The excavated material is not suitable as fill material within the proposed
building envelope but could be used as fill material in non-settlement sensitive areas such as landscaping
regions. In these non-settlement sensitive areas, the fill should be placed in maximum 12 inch thick lifts
that should be compacted to at least 90 percent of the modified proctor (ASTM D 1557 Test Method)
maximum dry density.
All existing foundation elements and any undocumented fill should be removed and backfilled with
suitable structural fill compacted to at least 95 percent of the modified proctor up to planned subgrade
elevations.
The native soils below the vegetation and topsoil consist of recessional outwash and at depth by glacial till.
These materials are generally considered suitable for use as structural fill provided they are within 3
percent of the optimum moisture content. It should be noted that glacial till soil materials are typically
suitable for structural fill during the summer months only if they can be dried to optimum moisture levels.
Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of 3 inches
and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve). Structural fill should be
placed in maximum lift thicknesses of 12 inches and should be compacted to a minimum of 95 percent of
the modified proctor maximum dry density, as determined by the ASTM D 1557 test method.
8.1.2 Temporary Excavations
Based on our understanding of the project, we anticipate that the grading could include local cuts on the
order of approximately 4 feet or less for foundation placement. These excavations should be sloped no
steeper than 1H:1V (Horizontal:Vertical) in native soils. If an excavation is subject to heavy vibration or
surcharge loads, we recommend that the excavations be sloped no steeper than 1.5H:1V, where room
permits. Excavations that extend below 4 feet during the wet season (October through May) should be
sloped no steeper than 1.5H:1V and 2H:1V if subject to surcharge loads.
Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part N,
Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a qualified
person during construction activities and the inspections should be documented in daily reports. The
contractor is responsible for maintaining the stability of the temporary cut slopes and reducing slope
erosion during construction.
Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather, and the
slopes should be closely monitored until the permanent retaining systems or slope configurations are
complete. Materials should not be stored or equipment operated within 10 feet of the top of any
temporary cut slope.
Soil conditions may not be completely known from the geotechnical investigation. In the case of
temporary cuts, the existing soil conditions may not be completely revealed until the excavation work
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exposes the soil. Typically, as excavation work progresses the maximum inclination of temporary slopes
will need to be re-evaluated by the geotechnical engineer so that supplemental recommendations can be
made. Soil and groundwater conditions can be highly variable. Scheduling for soil work will need to be
adjustable, to deal with unanticipated conditions, so that the project can proceed and required deadlines
can be met.
If any variations or undesirable conditions are encountered during construction, we should be notified so
that supplemental recommendations can be made. If room constraints or groundwater conditions do not
permit temporary slopes to be cut to the maximum angles allowed by the WAC, temporary shoring
systems may be required. The contractor should be responsible for developing temporary shoring
systems, if needed. We recommend that Cobalt Geosciences and the project structural engineer review
temporary shoring designs prior to installation, to verify the suitability of the proposed systems.
8.1.3 Erosion and Sediment Control
Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to wetlands,
streams, lakes, drainage systems, and adjacent properties. Erosion and sediment control measures
should be implemented and these measures should be in general accordance with local regulations. At a
minimum, the following basic recommendations should be incorporated into the design of the erosion
and sediment control features for the site:
Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance of the
site soils, to take place during the dry season (generally May through September). However, provided
precautions are taken using Best Management Practices (BMP’s), grading activities can be completed
during the wet season (generally October through April).
All site work should be completed and stabilized as quickly as possible.
Additional perimeter erosion and sediment control features may be required to reduce the possibility
of sediment entering the surface water. This may include additional silt fences, silt fences with a
higher Apparent Opening Size (AOS), construction of a berm, or other filtration systems.
Any runoff generated by dewatering discharge should be treated through construction of a sediment
trap if there is sufficient space. If space is limited other filtration methods will need to be
incorporated.
8.1.4 Foundation Design
A future single family residence located in the new lot may be supported on a shallow spread footing
foundation system bearing on re-compacted native soils or on properly compacted structural fill placed on
the suitable, re-compacted native soils. If structural fill is used to support foundations, then the zone of
structural fill should extend beyond the faces of the footing a lateral distance at least equal to the
thickness of the structural fill.
We recommend re-compaction of the upper 3 feet of native soils below proposed footing elevations due to
localized loose soil conditions (where recessional outwash is present). The width of compaction should
extend at least 3 feet from the edges of all footings. Soils should be compacted to at least 95 percent of the
modified proctor.
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If undocumented fill is encountered below foundation elements, it should be removed and replaced with
suitable native soils or imported structural fill. As noted above, overexcavations should extend laterally
from the footing edges a distance equal to the depth of the overexcavation.
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 structure. Provided that the
footings are supported as recommended above, a net allowable bearing pressure of 2,000 pounds per
square foot (psf) may be used for design.
A 1/3 increase in the above value may be used for short duration loads, such as those imposed by wind
and seismic events. Structural fill placed on bearing, native subgrade should be compacted to at least 95
percent of the maximum dry density based on ASTM Test Method D1557. Footing excavations should be
inspected to verify that the foundations will bear on suitable material.
Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or adjacent
exterior grade, whichever is lower. Interior footings should have a minimum depth of 12 inches below pad
subgrade (soil grade) or adjacent exterior grade, whichever is lower.
If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch.
Differential settlement, along a 25-foot exterior wall footing, or between adjoining column footings,
should be less than ½ inch. This translates to an angular distortion of 0.002. Most settlement is
expected to occur during construction, as the loads are applied. However, additional post-construction
settlement may occur if the foundation soils are flooded or saturated. All footing excavations should be
observed by a qualified geotechnical consultant.
Resistance to lateral footing displacement can be determined using an allowable friction factor of 0.35
acting between the base of foundations and the supporting subgrades. Lateral resistance for footings can
also be developed using an allowable equivalent fluid passive pressure of 275 pounds per cubic foot (pcf)
acting against the appropriate vertical footing faces (neglect the upper 12 inches below grade in exterior
areas). The allowable friction factor and allowable equivalent fluid passive pressure values include a
factor of safety of 1.5. The frictional and passive resistance of the soil may be combined without reduction
in determining the total lateral resistance. A 1/3 increase in the above values may be used for short
duration transient loads.
Care should be taken to prevent wetting or drying of the bearing materials during construction. Any
extremely wet or dry materials, or any loose or disturbed materials at the bottom of the footing
excavations, should be removed prior to placing concrete. The potential for wetting or drying of the
bearing materials can be reduced by pouring concrete as soon as possible after completing the footing
excavation and evaluating the bearing surface by the geotechnical engineer or his representative.
8.1.5 Infiltration Recommendations
We understand that some portion of stormwater runoff will flow into infiltration trenches or drywells. We
should be provided with the final system designs in order to determine if they are consistent with our
recommendations.
The soils encountered in the test pits consisted of generally medium grained sand with variable amounts
of silt. We recommend that any trench extend into the cleaner outwash, which was encountered about 2.5
to 3 feet below existing grades. Due to soil mottling and the possibility of shallow perched groundwater,
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we recommend that any drywells extend no deeper than 5 feet below grade. Any system should be located
along the east property line.
We should be provided with final plans for review to determine if the intent of our recommendations has
been incorporated or if additional modifications are needed. Verification testing of infiltration systems
should be performed during construction.
8.1.6 Slab-on-Grade
We recommend that the upper 24 inches of the existing soils within any proposed slab areas be re-
compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method).
Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor barrier could
result in curling of the concrete slab at joints. Floor covers sensitive to moisture typically requires the
usage of a vapor barrier. A materials or structural engineer should be consulted regarding the detailing of
the vapor barrier below concrete slabs. Exterior slabs typically do not utilize vapor barriers.
The American Concrete Institutes ACI 360R-06 Design of Slabs on Grade and ACI 302.1R-04 Guide for
Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor
slab detailing.
Slabs on grade may be designed using a coefficient of subgrade reaction of 180 pounds per cubic inch (pci)
assuming the slab-on-grade base course is underlain by structural fill placed and compacted as outlined in
Section 8.1.
A perimeter drainage system is recommended unless interior slab areas are elevated a minimum of 12
inches above adjacent exterior grades. If installed, a perimeter drainage system should consist of a 4 inch
diameter perforated drain pipe surrounded by a minimum 6 inches of drain rock wrapped in a non-woven
geosynthetic filter fabric to reduce migration of soil particles into the drainage system. The perimeter
drainage system should discharge by gravity flow to a suitable stormwater system.
Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate surface
water flow away from these buildings and preferably with a relatively impermeable surface cover
immediately adjacent to the buildings.
8.1.7 Utilities
Utility trenches should be excavated according to accepted engineering practices following OSHA
(Occupational Safety and Health Administration) standards, by a contractor experienced in such work.
The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench
walls should be reduced; cyclic wetting and drying of excavation side slopes should be avoided.
Depending upon the location and depth of some utility trenches, groundwater flow into open excavations
could be experienced, especially during or shortly following periods of precipitation.
In general, sandy soils were encountered at shallow depths in the explorations at this site. These soils
have low cohesion and have a tendency to cave or slough in excavations. Shoring or sloping back trench
sidewalls is required within these soils.
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All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility trench
backfill placed in or adjacent to buildings and exterior slabs should be compacted to at least 95 percent of
the maximum dry density based on ASTM Test Method D1557. The upper 5 feet of utility trench backfill
placed in pavement areas should be compacted to at least 95 percent of the maximum dry density based
on ASTM Test Method D1557. Below 5 feet, utility trench backfill in pavement areas should be compacted
to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. Pipe bedding
should be in accordance with the pipe manufacturer's recommendations.
The contractor is responsible for removing all water-sensitive soils from the trenches regardless of the
backfill location and compaction requirements. Depending on the depth and location of the proposed
utilities, we anticipate the need to re-compact existing fill soils below the utility structures and pipes. The
contractor should use appropriate equipment and methods to avoid damage to the utilities and/or
structures during fill placement and compaction procedures.
8.1.8 Groundwater Influence on Construction
At the time of our investigation, groundwater was not encountered in any of the explorations. Based on
the soil conditions and area geology, we do not expect significant amounts of groundwater to be
encountered during construction at this site. Light volumes of perched groundwater could be
encountered locally and at depths greater than about 8 feet.
8.1.9 Pavement Recommendations
The near surface subgrade soils generally consist of silty sand with gravel and poorly graded sand with
variable amounts of gravel. These soils are rated as fair to good for pavement subgrade material
(depending on silt content and moisture conditions). We estimate that the subgrade will have a California
Bearing Ratio (CBR) value of 8 and a modulus of subgrade reaction value of k = 180 pci, provided the
subgrade is prepared in general accordance with our recommendations.
We recommend that, at a minimum, 18 inches of the existing subgrade material be moisture conditioned
(as necessary) and re-compacted to prepare for the construction of pavement sections. Deeper levels of
recompaction or overexcavation and replacement may be necessary in areas where fill and/or loose soils
are present.
The subgrade should be compacted to at least 95 percent of the maximum dry density as determined by
ASTM Test Method D1557. In place density tests should be performed to verify proper moisture content
and adequate compaction. However, if the subgrade soil consists of firm and unyielding native glacial
soils a proof roll of the pavement subgrade soil may be performed in lieu of compaction tests.
The recommended flexible and rigid pavement sections are based on design CBR and modulus of
subgrade reaction (k) values that are achieved, only following proper subgrade preparation. It should be
noted that subgrade soils that have relatively high silt contents will likely be highly sensitive to moisture
conditions. The subgrade strength and performance characteristics of a silty subgrade material may be
dramatically reduced if this material becomes wet.
Based on our knowledge of the proposed project, we expect the traffic to range from light duty (passenger
automobiles) to heavy duty (delivery trucks). The following tables show the recommended pavement
sections for light duty and heavy duty use.
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ASPHALTIC CONCRETE (FLEXIBLE) PAVEMENT
LIGHT DUTY
Asphaltic Concrete Aggregate Base* Compacted Subgrade* **
2.0 in. 6.0 in. 18.0 in.
* 95% compaction based on ASTM Test Method D1557
** A proof roll may be performed in lieu of in place density tests
HEAVY DUTY
Asphaltic Concrete Aggregate Base* Compacted Subgrade* **
3.0 in. 6.0 in. 18.0 in.
* 95% compaction based on ASTM Test Method D1557
** A proof roll may be performed in lieu of in place density tests
PORTLAND CEMENT CONCRETE (RIGID) PAVEMENT
Min. PCC Depth Aggregate Base* Compacted Subgrade*
**
6.0 in. 6.0 in. 12.0 in.
* 95% compaction based on ASTM Test Method D1557
** A proof roll may be performed in lieu of in place density tests
The asphaltic concrete depth in the flexible pavement tables should be a surface course type asphalt, such
as Washington Department of Transportation (WSDOT) ½ inch HMA. The rigid pavement design is
based on a Portland Cement Concrete (PCC) mix that has a 28 day compressive strength of 4,000 pounds
per square inch (psi). The design is also based on a concrete flexural strength or modulus of rupture of
550 psi.
9.0 Construction Field Reviews
Cobalt Geosciences should be retained to provide part time field review during construction in order to
verify that the soil conditions encountered are consistent with our design assumptions and that the intent
of our recommendations is being met. This will require field and engineering review to:
Monitor and test structural fill placement and soil compaction
Verify the soil bearing at foundation locations for the buildings
Verify slab subgrade and capillary break material below slab-on-grade
Observe footing drainage placement
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Verify infiltration rates at system locations
Observe proof rolls of roadway subgrade prior to asphalt placement
Geotechnical design services should also be anticipated during the subsequent final design phase to
support the structural design and address specific issues arising during this phase. Field and engineering
review services will also be required during the construction phase in order to provide a Final Letter for
the project.
10.0 Closure
This report was prepared for the exclusive use of Janet Wixom and Rita Berg and their appointed
consultants. Any use of this report or the material contained herein by third parties, or for other than the
intended purpose, should first be approved in writing by Cobalt Geosciences, LLC.
The recommendations contained in this report are based on assumed continuity of soils with those of our
test holes, and assumed structural loads. Cobalt Geosciences should be provided with final architectural
and civil drawings when they become available in order that we may review our design recommendations
and advise of any revisions, if necessary.
Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is the
responsibility of Janet Wixom and Rita Berg who is identified as “the Client” within the Statement of
General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences should any of
these not be satisfied.
Respectfully submitted,
Cobalt Geosciences
Original signed by: Original signed by:
3/13/17
Phil Haberman, P.G., P.E.G. Sean Caraway, P.E.
Principal Engineering Geologist Senior Geotechnical Engineer
PH/sc
APPENDIX A
Statement of General Conditions
Statement of General Conditions
USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its agent and
may not be used by any third party without the express written consent of Cobalt Geosciences and the
Client. Any use which a third party makes of this report is the responsibility of such third party.
BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this report are
in accordance with Cobalt Geosciences present understanding of the site specific project as described by
the Client. The applicability of these is restricted to the site conditions encountered at the time of the
investigation or study. If the proposed site specific project differs or is modified from what is described in
this report or if the site conditions are altered, this report is no longer valid unless Cobalt Geosciences is
requested by the Client to review and revise the report to reflect the differing or modified project specifics
and/or the altered site conditions.
STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in
accordance with the normally accepted standard of care in the state of execution for the specific
professional service provided to the Client. No other warranty is made.
INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and
statements regarding their condition, made in this report are based on site conditions encountered by
Cobalt Geosciences at the time of the work and at the specific testing and/or sampling locations.
Classifications and statements of condition have been made in accordance with normally accepted
practices which are judgmental in nature; no specific description should be considered exact, but rather
reflective of the anticipated material behavior. Extrapolation of in situ conditions can only be made to
some limited extent beyond the sampling or test points. The extent depends on variability of the soil, rock
and groundwater conditions as influenced by geological processes, construction activity, and site use.
VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be
encountered that are different from those described in this report or encountered at the test locations,
Cobalt Geosciences must be notified immediately to assess if the varying or unexpected conditions are
substantial and if reassessments of the report conclusions or recommendations are required. Cobalt
Geosciences will not be responsible to any party for damages incurred as a result of failing to notify Cobalt
Geosciences that differing site or sub-surface conditions are present upon becoming aware of such
conditions.
PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and specifications
should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next project stage (property
acquisition, tender, construction, etc), to confirm that this report completely addresses the elaborated
project specifics and that the contents of this report have been properly interpreted. Specialty quality
assurance services (field observations and testing) during construction are a necessary part of the
evaluation of sub-subsurface conditions and site preparation works. Site work relating to the
recommendations included in this report should only be carried out in the presence of a qualified
geotechnical engineer; Cobalt Geosciences cannot be responsible for site work carried out without being
present.
10.2
APPENDIX B
Figures: Vicinity Map, Site Plan
N
VICINITY MAP
FIGURE 1
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
cobaltgeo@gmail.comCobalt
Geosciences
Proposed Single Family Residence
532 Edmonds Avenue NE
Renton, Washington
Project
Location
Renton
WASHINGTON
SITE
SITE PLAN
FIGURE 2
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
cobaltgeo@gmail.comCobalt
Geosciences
N
Proposed Single Family Residence
532 Edmonds Avenue NE
Renton, Washington
TP-1
TP-2
TP-1
APPENDIX C
Test Pit Logs
SP-
SM
SP
Topsoil/Grass
SP-SM; Loose to medium dense, silty-fine to medium grained sand trace
gravel, yellowish brown to grayish brown, moist. (Recessional Outwash)
SP; Loose to medium dense, fine to medium grained sand with graveland trace silt, mottled yellowish brown to grayish brown, pieces of
cemented till below 6 feet, moist. (Recessional Outwash)
Test pit terminated at 8 feet.
DRILLING / INSTALLATION:
STARTED
STATIC DTW (ft):Not Encountered
COMPLETED:
LOGGED BY:PH
DRILLING METHOD:
SAMPLING EQUIPMENT:Grab
PROJECT NUMBER:
PROJECT:Proposed Subdivision
2/9/17 2/9/17
PAGE 1 OF 1
USCSGraphicLogDRILLING COMPANY:Provided GROUND ELEV (ft):
TP-1
DRILLING EQUIPMENT:Excavator
Description
TOC ELEV (ft):
BOREHOLE DEPTH (ft):8.0
BOREHOLE DIA. (in):
CHECKED BY:SC
NORTHING (ft):EASTING (ft):
Test Pit No:
LOCATION:532 Edmonds Ave N
INITIAL DTW (ft):Not Encountered
LAT:LONG:Depth(feet)5.0
WELL CASING DIA. (in):---
WELL DEPTH (ft):---Depth(feet)5BlowCountRecov.(feet)HeadspacePID(ppm)TimeSample ID
Sample
SP-
SM
SP
Topsoil/Grass
SP-SM; Loose to medium dense, silty-fine to medium grained sand trace
gravel, yellowish brown to grayish brown, moist. (Recessional Outwash)
SP; Loose to medium dense, fine to medium grained sand with graveland trace silt, mottled yellowish brown to grayish brown, moist.(Recessional Outwash)
Test pit terminated at 8 feet.
DRILLING / INSTALLATION:
STARTED
STATIC DTW (ft):Not Encountered
COMPLETED:
LOGGED BY:PH
DRILLING METHOD:
SAMPLING EQUIPMENT:Grab
PROJECT NUMBER:
PROJECT:Proposed Subdivision
2/9/17 2/9/17
PAGE 1 OF 1
USCSGraphicLogDRILLING COMPANY:Provided GROUND ELEV (ft):
TP-2
DRILLING EQUIPMENT:Excavator
Description
TOC ELEV (ft):
BOREHOLE DEPTH (ft):8.0
BOREHOLE DIA. (in):
CHECKED BY:SC
NORTHING (ft):EASTING (ft):
Test Pit No:
LOCATION:532 Edmonds Ave N
INITIAL DTW (ft):Not Encountered
LAT:LONG:Depth(feet)5.0
WELL CASING DIA. (in):---
WELL DEPTH (ft):---Depth(feet)5BlowCountRecov.(feet)HeadspacePID(ppm)TimeSample ID
Sample