HomeMy WebLinkAboutRS_Geotechnical_Report_181116_v1Cobalt
Geosciences
Geotechnical Investigation
Proposed Additions
3811 NE 21st Street
Renton, Washington
January 19, 2018
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
i
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 .................................................................................................. 4
8.1.1 Site Preparation ................................................................................................... 4
8.1.2 Temporary Excavations ........................................................................................ 5
8.1.3 Erosion and Sediment Control.............................................................................. 6
8.1.4 Foundation Design ............................................................................................... 6
8.1.5 Stormwater Management ..................................................................................... 7
8.1.6 Slab-on-Grade ...................................................................................................... 7
8.1.7 Utilities ................................................................................................................ 8
8.1.8 Groundwater Influence on Construction .............................................................. 9
8.1.9 Pavements ............................................................................................................ 9
9.0 CONSTRUCTION FIELD REVIEWS ...........................................................................10
10.0 CLOSURE ...................................................................................................................10
LIST OF APPENDICES
Appendix A — Statement of General Conditions
Appendix B — Figures
Appendix C — Test Pit Logs
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
1
P.O. Box 82243, Kenmore, WA 98028
1.0 Introduction
In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a geotechnical
investigation for the proposed building and parking lot additions to the First Ukrainian Pentecostal
Church located at 3811 NE 21st Street in Renton, Washington (Figure 1).
The purpose of the geotechnical investigation was to identify subsurface conditions and to provide
geotechnical recommendations for foundation design, earthwork, soil compaction, utilities, general
pavement guidelines, drainage, 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 parking lot expansions, a building addition, and stormwater infrastructure
construction within the two developed parc els. We anticipate that the building addition will include a
crawlspace and wood framing with light foundation loading. Parking lot expansions will likely include
converting existing graveled areas into asphalt paved parking stalls and drivelanes.
Stormwater management may include permeable pavements, shallow rain gardens, or bioswales near the
parking lots.
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 parking lot construction. We should be
provided with the final plans to verify that our recommendations have been incorporated and considered.
3.0 Site Description
The site is located at 3811 NE 21st Street in Renton, Washington (Figure 1). The property consists of three
rectangular shaped parcels (No’s 0423059237, 0423059068, and 0423059307) with a total area of about
3.4 acres.
The north portion of the property is developed with a church and paved parking areas. The east portion is
partially developed with a paved and gravel parking lot. The south parcel is developed with a si ngle-
family residence.
The south parcel slopes gently to moderately downward toward the south. The north half slopes gently
toward the east. There are several short landscaping walls near the building. The overall topographic
relief is about 15 feet.
The site is vegetated with grasses, sparse deciduous trees, Fir trees, and various bushes and shrubs. The
site is bordered to the east and west by single-family residences, to the north by NE 21 Street, and to the
south by NE 19th Street.
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
2
4.0 Field Investigation
4.1.1 Site Investigation Program
The geotechnical field investigation program was completed on December 13, 2017 and included
excavating and sampling three 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 hand boring, and observed and recorded pertinent site features.
The results of the test pit and hand boring 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 separat e
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 Geologic Map of the Renton Quadrangle, indicates that the site is 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 6 inches of topsoil and grass underlain by about 2.5 feet of loose,
silty-fine to medium grained sand with gravel, debris, and organic material (Fill). This layer was
underlain by approximately 2 feet of loose to medium dense, silty-fine to medium grained sand with
gravel (Weathered Glacial Till). This layer was underlain by dense, silty-fine to medium grained sand
with gravel (Glacial Till), which continued to the termination depth of the test pit.
Test Pit TP-2
Test Pit TP-2 encountered approximately 2 inches of gravel underlain by about 2 feet of medium dense,
silty-fine to medium grained sand with gravel (Weathered Glacial Till). This layer was underlain by dense
to very dense, silty-fine to medium grained sand with gravel (Glacial Till), which continued to the
termination depth of the test pit.
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
3
Test Pit TP-3
Test Pit TP-3 encountered approximately 6 inches of topsoil and grass underlain by about 7.5 feet of loose,
silty-fine to medium grained sand with gravel, debris, and organic material (Fill). This layer was
underlain by medium dense, silty-fine to medium grained sand with gravel (Weathered Glacial Till),
which continued to the termination depth of the test pit.
5.1.2 Groundwater
At the time of our investigation, groundwater was encountered in TP-1 at 3.5 feet below grade and in TP-3
at 8 feet below grade. The groundwater appears to be perched between loose fill and underlying glacial
till. There is a stormwater pond and large open vault just north and east of the site (two locations).
Groundwater is likely migrating laterally into the property from these locations.
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 Alderwood gravelly sandy loam (8 to 15 percent slopes). We anticipate the soils to consist of
gravelly sandy loams with a “Slight” 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 dense to
very dense soils within the upper 100 feet.
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:
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
4
PGA (Peak Ground Acceleration, in percent of g)
SS 141.50% 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 groundwate r table.
The relatively dense soil deposits that underlie the site have a low potential for liquefaction.
7.0 DISCUSSION
7.1.1 General
It is our opinion that the proposed addition may be supported on 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 silty-sand with gravel. In general, suitable bearing
soils (medium dense or firmer) in the area of the addition were encountered about 2 feet below grade.
The gravel parking lot is locally underlain by loose fill that will not be suitable for use as structural fill.
Local overexcavation up to 3 feet below grade will likely be necessary as part of parking lot sub grade
preparation.
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 wi ll
range from 6 to 18 inches. Deeper fill with organic material extended up to 4 feet below grade in the east
parking lot and 8 feet or more in the south portion of the site.
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.
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
5
The native soils below the vegetation and topsoil consist of weathered 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 stee per than 1.5H:1V, where room
permits. Temporary excavations in fill should be sloped no steeper than 1.5H:1V and 2H:1V with
surcharges.
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
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.
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
6
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 exca vation 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
Building additions may be supported on shallow spread footing foundation systems bearing on
undisturbed medium dense or firmer native soils, re-compacted native soils, or on properly compacted
structural fill placed on the suitable 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.
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 2,500 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 o n 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
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
7
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 increas e 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 Stormwater Management
Permeable pavements may be considered as part of the stormwater management system for the project.
The site is not located near areas with erosion or steep slope hazards or adjacent to structures with
basements.
Typically, pervious pavements are supported by a leveling course and storage reservoir course placed on
prepared native soils. These courses typically consist of open graded angular rock, 5/8 to 2 inches in
diameter, with a total thickness ranging from 6 to 18 inches.
We recommend removal of loose topsoil prior to placement of the clean crushed rock. The exp osed
subgrades should NOT be re-compacted to 95 percent of the modified proctor as is typical for roadway
and parking lot subgrade preparation.
We should be on site to verify ‘firm and unyielding’ soil conditions are present prior to rock placement.
For this site, this generally equates to a relative soil compaction of 90 to 92 percent of the standard
proctor. An underdrain system should be incorporated to remove excess runoff and to cutoff lateral
interflow along the site perimeter. We can provide add itional recommendations upon request and once
the civil design plans have been prepared.
We should be provided with the final design to verify that these recommendations have been
incorporated. Field verification of soil conditions by the geotechnical engineer is recommended during
construction.
8.1.6 Slab-on-Grade
We recommend that the upper 18 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
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
8
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 followin g periods of precipitation.
In general, both silty and 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.
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 per cent 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.
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
9
8.1.8 Groundwater Influence on Construction
At the time of our investigation, groundwater was encountered in TP-1 at 3.5 feet below grade in and in
TP-3 at about 8 feet below grade. Light to moderate volumes of perched groundwater should be expected
in excavations during the wetter months of the year. Typical sump exca vations and pumps should
adequately de-water utility trenches or other excavations where groundwater is encountered. The
contractor is responsible for groundwater removal.
8.1.9 Pavement Recommendations
The near surface subgrade soils generally consist of silty sand with 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.
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
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
10
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. 18.0 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
▪ 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 aris ing 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 Andrey Kozak and his 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.
GEOTECHNICAL INVESTIGATION
RENTON, WASHINGTON
January 19, 2018
11
The recommendations contained in this report are based on assumed c ontinuity 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 Andrey Kozak 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, LLC
Original signed by:
Exp. 6-26-2018
Phil Haberman, PE, LG, LEG
Principal
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 modif ied 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, b ut 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.com
Cobalt
Geosciences
Project
Location
Renton
WASHINGTON
SITE
Geotechnical Investigation
3811 NE 21st Street
Renton, Washington
SITE PLAN
FIGURE 2
P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
cobaltgeo@gmail.com
Cobalt
Geosciences
N
Geotechnical Investigation
3811 NE 21st Street
Renton, Washington
TP-1
TP-3
TP-2
TP-1
APPENDIX C
Test Pit Logs
TEST PIT LOGS P.O. Box 82243
Kenmore, WA 98028
(206) 331-1097
cobaltgeo@gmail.com
Cobalt
Geosciences
Test Pit TP-1
0-0.5’ Vegetation/Topsoil
0.5-3’ Silty Sand with Gravel (SM)
Loose, silty-fine to medium grained sand
with gravel and debris, mottled yellowish brown to grayish brown,
moist. (Fill)
3-5’ Silty Sand with Gravel (SM)
Loose to medium dense, silty-fine to medium grained sand
with gravel, yellowish brown to grayish brown, moist.
(Weathered Glacial Till)
5-6’ Silty Sand with Gravel (SM)
Medium dense to dense, silty-fine to medium grained sand
with gravel, grayish brown, moist. (Glacial Till)
End of Test Pit 6’
Moderate Groundwater at 3.5’
Some Caving 0-3’
SM
SM
Weathered Glacial
Till
Topsoil/Vegetation
Glacial Till
0.5’
5’
Test Pit TP-3 0-0.5’ Vegetation/Topsoil
0.5-8’ Silty Sand with Gravel (SM)
Very loose to loose, silty-fine to medium grained sand
with gravel and debris/garbage, dark yellowish brown,
moist. (Fill)
8-8.5’ Silty Sand with Gravel (SM)
Medium dense, silty-fine to medium grained sand
with gravel, mottled yellowish brown to grayish brown, moist to wet.
(Weathered Glacial Till)
End of Test Pit 8.5’
Heavy Groundwater at 8’
Severe Caving 0 to 8’
SM
SM Fill
Fill
Weathered Glacial Till
0.5’
8’
USCS Graphic
USCS Graphic
Geotechnical Investigation
3811 NE 21st Street
Renton, Washington
3’
Topsoil/Vegetation
LLC
SM
Test Pit TP-2
0-0.2’ Gravel
0.8-4.5’ Silty Sand with Gravel (SM)
Dense to very dense, silty-fine to medium grained sand
with gravel, mottled yellowish brown to grayish brown,
moist. (Glacial Till)
End of Test Pit 4.5’
No Groundwater
No Caving
SM
Gravel
Glacial Till
0.2’
USCS Graphic