HomeMy WebLinkAboutRS_Geotechnical_Report_251209_v1EarthSolutionsNWLLC
EarthSolutions
NW LLC
15365 N.E.90th Street,Suite 100 Redmond,WA 98052
(425)449-4704 Fax (425)449-4711
www.earthsolutionsnw.com
Geotechnical Engineering
Construction Observation/Testing
Environmental Services
GEOTECHNICAL ENGINEERING STUDY
PROPOSED SINGLE-FAMILY RESIDENCES
TALBOT HILLS SHORT PLAT
XXX SOUTH 55 STREET
RENTON,WASHINGTON
ES-9182
TH
PREPARED FOR
SCHNEIDER FAMILY HOMES, LLC
August 8, 2023
_________________________
Samuel E. Suruda, L.G.
Senior Staff Geologist
_________________________
Stephen H. Avril
Project Manager
_________________________
Kyle R. Campbell, P.E.
Senior Principal Engineer
GEOTECHNICAL ENGINEERING STUDY
PROPOSED SINGLE-FAMILY RESIDENCES
TALBOT HILLS SHORT PLAT
XXX SOUTH 55TH STREET
RENTON, WASHINGTON
ES-9182
Earth Solutions NW, LLC
15365 Northeast 90th Street, Suite 100
Redmond, Washington 98052
Phone: 425-449-4704 | Fax: 425-449-4711
www.earthsolutionsnw.com
08/08/2023
Geotechnical-Engineering Report
Important Information about This
Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.
While you cannot eliminate all such risks, you can manage them. The following information is provided to help.
The Geoprofessional Business Association (GBA)
has prepared this advisory to help you – assumedly
a client representative – interpret and apply this
geotechnical-engineering report as effectively as
possible. In that way, you can benefit from a lowered
exposure to problems associated with subsurface
conditions at project sites and development of
them that, for decades, have been a principal cause
of construction delays, cost overruns, claims,
and disputes. If you have questions or want more
information about any of the issues discussed herein,
contact your GBA-member geotechnical engineer.
Active engagement in GBA exposes geotechnical
engineers to a wide array of risk-confrontation
techniques that can be of genuine benefit for
everyone involved with a construction project.
Understand the Geotechnical-Engineering Services
Provided for this Report
Geotechnical-engineering services typically include the planning,
collection, interpretation, and analysis of exploratory data from
widely spaced borings and/or test pits. Field data are combined
with results from laboratory tests of soil and rock samples obtained
from field exploration (if applicable), observations made during site
reconnaissance, and historical information to form one or more models
of the expected subsurface conditions beneath the site. Local geology
and alterations of the site surface and subsurface by previous and
proposed construction are also important considerations. Geotechnical
engineers apply their engineering training, experience, and judgment
to adapt the requirements of the prospective project to the subsurface
model(s). Estimates are made of the subsurface conditions that
will likely be exposed during construction as well as the expected
performance of foundations and other structures being planned and/or
affected by construction activities.
The culmination of these geotechnical-engineering services is typically a
geotechnical-engineering report providing the data obtained, a discussion
of the subsurface model(s), the engineering and geologic engineering
assessments and analyses made, and the recommendations developed
to satisfy the given requirements of the project. These reports may be
titled investigations, explorations, studies, assessments, or evaluations.
Regardless of the title used, the geotechnical-engineering report is an
engineering interpretation of the subsurface conditions within the context
of the project and does not represent a close examination, systematic
inquiry, or thorough investigation of all site and subsurface conditions.
Geotechnical-Engineering Services are Performed
for Specific Purposes, Persons, and Projects,
and At Specific Times
Geotechnical engineers structure their services to meet the specific
needs, goals, and risk management preferences of their clients. A
geotechnical-engineering study conducted for a given civil engineer
will not likely meet the needs of a civil-works constructor or even a
different civil engineer. Because each geotechnical-engineering study
is unique, each geotechnical-engineering report is unique, prepared
solely for the client.
Likewise, geotechnical-engineering services are performed for a specific
project and purpose. For example, it is unlikely that a geotechnical-
engineering study for a refrigerated warehouse will be the same as
one prepared for a parking garage; and a few borings drilled during
a preliminary study to evaluate site feasibility will not be adequate to
develop geotechnical design recommendations for the project.
Do not rely on this report if your geotechnical engineer prepared it:
• for a different client;
• for a different project or purpose;
• for a different site (that may or may not include all or a portion of
the original site); or
• before important events occurred at the site or adjacent to it;
e.g., man-made events like construction or environmental
remediation, or natural events like floods, droughts, earthquakes,
or groundwater fluctuations.
Note, too, the reliability of a geotechnical-engineering report can
be affected by the passage of time, because of factors like changed
subsurface conditions; new or modified codes, standards, or
regulations; or new techniques or tools. If you are the least bit uncertain
about the continued reliability of this report, contact your geotechnical
engineer before applying the recommendations in it. A minor amount
of additional testing or analysis after the passage of time – if any is
required at all – could prevent major problems.
Read this Report in Full
Costly problems have occurred because those relying on a geotechnical-
engineering report did not read the report in its entirety. Do not rely on
an executive summary. Do not read selective elements only. Read and
refer to the report in full.
You Need to Inform Your Geotechnical Engineer
About Change
Your geotechnical engineer considered unique, project-specific factors
when developing the scope of study behind this report and developing
the confirmation-dependent recommendations the report conveys.
Typical changes that could erode the reliability of this report include
those that affect:
• the site’s size or shape;
• the elevation, configuration, location, orientation,
function or weight of the proposed structure and
the desired performance criteria;
• the composition of the design team; or
• project ownership.
As a general rule, always inform your geotechnical engineer of project
or site changes – even minor ones – and request an assessment of their
impact. The geotechnical engineer who prepared this report cannot accept
responsibility or liability for problems that arise because the geotechnical
engineer was not informed about developments the engineer otherwise
would have considered.
Most of the “Findings” Related in This Report
Are Professional Opinions
Before construction begins, geotechnical engineers explore a site’s
subsurface using various sampling and testing procedures. Geotechnical
engineers can observe actual subsurface conditions only at those specific
locations where sampling and testing is performed. The data derived from
that sampling and testing were reviewed by your geotechnical engineer,
who then applied professional judgement to form opinions about
subsurface conditions throughout the site. Actual sitewide-subsurface
conditions may differ – maybe significantly – from those indicated in
this report. Confront that risk by retaining your geotechnical engineer
to serve on the design team through project completion to obtain
informed guidance quickly, whenever needed.
This Report’s Recommendations Are
Confirmation-Dependent
The recommendations included in this report – including any options or
alternatives – are confirmation-dependent. In other words, they are not
final, because the geotechnical engineer who developed them relied heavily
on judgement and opinion to do so. Your geotechnical engineer can finalize
the recommendations only after observing actual subsurface conditions
exposed during construction. If through observation your geotechnical
engineer confirms that the conditions assumed to exist actually do exist,
the recommendations can be relied upon, assuming no other changes have
occurred. The geotechnical engineer who prepared this report cannot assume
responsibility or liability for confirmation-dependent recommendations if you
fail to retain that engineer to perform construction observation.
This Report Could Be Misinterpreted
Other design professionals’ misinterpretation of geotechnical-
engineering reports has resulted in costly problems. Confront that risk
by having your geotechnical engineer serve as a continuing member of
the design team, to:
• confer with other design-team members;
• help develop specifications;
• review pertinent elements of other design professionals’ plans and
specifications; and
• be available whenever geotechnical-engineering guidance is needed.
You should also confront the risk of constructors misinterpreting this
report. Do so by retaining your geotechnical engineer to participate in
prebid and preconstruction conferences and to perform construction-
phase observations.
Give Constructors a Complete Report and Guidance
Some owners and design professionals mistakenly believe they can shift
unanticipated-subsurface-conditions liability to constructors by limiting
the information they provide for bid preparation. To help prevent
the costly, contentious problems this practice has caused, include the
complete geotechnical-engineering report, along with any attachments
or appendices, with your contract documents, but be certain to note
conspicuously that you’ve included the material for information purposes
only. To avoid misunderstanding, you may also want to note that
“informational purposes” means constructors have no right to rely on
the interpretations, opinions, conclusions, or recommendations in the
report. Be certain that constructors know they may learn about specific
project requirements, including options selected from the report, only
from the design drawings and specifications. Remind constructors
that they may perform their own studies if they want to, and be sure to
allow enough time to permit them to do so. Only then might you be in
a position to give constructors the information available to you, while
requiring them to at least share some of the financial responsibilities
stemming from unanticipated conditions. Conducting prebid and
preconstruction conferences can also be valuable in this respect.
Read Responsibility Provisions Closely
Some client representatives, design professionals, and constructors do
not realize that geotechnical engineering is far less exact than other
engineering disciplines. This happens in part because soil and rock on
project sites are typically heterogeneous and not manufactured materials
with well-defined engineering properties like steel and concrete. That
lack of understanding has nurtured unrealistic expectations that have
resulted in disappointments, delays, cost overruns, claims, and disputes.
To confront that risk, geotechnical engineers commonly include
explanatory provisions in their reports. Sometimes labeled “limitations,”
many of these provisions indicate where geotechnical engineers’
responsibilities begin and end, to help others recognize their own
responsibilities and risks. Read these provisions closely. Ask questions.
Your geotechnical engineer should respond fully and frankly.
Geoenvironmental Concerns Are Not Covered
The personnel, equipment, and techniques used to perform an
environmental study – e.g., a “phase-one” or “phase-two” environmental
site assessment – differ significantly from those used to perform a
geotechnical-engineering study. For that reason, a geotechnical-engineering
report does not usually provide environmental findings, conclusions, or
recommendations; e.g., about the likelihood of encountering underground
storage tanks or regulated contaminants. Unanticipated subsurface
environmental problems have led to project failures. If you have not
obtained your own environmental information about the project site,
ask your geotechnical consultant for a recommendation on how to find
environmental risk-management guidance.
Obtain Professional Assistance to Deal with
Moisture Infiltration and Mold
While your geotechnical engineer may have addressed groundwater,
water infiltration, or similar issues in this report, the engineer’s
services were not designed, conducted, or intended to prevent
migration of moisture – including water vapor – from the soil
through building slabs and walls and into the building interior, where
it can cause mold growth and material-performance deficiencies.
Accordingly, proper implementation of the geotechnical engineer’s
recommendations will not of itself be sufficient to prevent
moisture infiltration. Confront the risk of moisture infiltration by
including building-envelope or mold specialists on the design team.
Geotechnical engineers are not building-envelope or mold specialists.
Copyright 2019 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly
prohibited, except with GBA’s specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of
GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element of a report of any kind.
Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent or intentional (fraudulent) misrepresentation.
Telephone: 301/565-2733
e-mail: info@geoprofessional.org www.geoprofessional.org
August 8, 2023
ES-9182
Schneider Family Homes, LLC
6510 Southcenter Boulevard, Suite 1
Tukwila, Washington 98188
Attention: Zach Schneider
Dear Zach:
Earth Solutions NW, LLC (ESNW), is pleased to present this geotechnical engineering study to
support the proposed residential development. Based on the results of our investigation, the
proposed project is feasible from a geotechnical standpoint. Our study indicates the site is
underlain primarily by competent glacial till.
In our opinion, the proposed residential structures can be supported on a conventional spread
and continuous footing system bearing on undisturbed competent native soil, compacted native
soil, or new structural fill. Generally speaking, we anticipate competent native soil suitable for
support of foundations will be encountered at the typical footing subgrade excavation depth
(roughly 18 to 24 inches below grade) with exception of fill observed at test location TP-4 which
was observed to a depth of four and one-half feet. The fill observed at TP-4 will need to be
removed and replaced to a depth below the observed topsoil at three feet. This material should
be replaced following compaction of the material left in-place following the overexcavation of fill.
Where loose or unsuitable soil conditions are encountered at foundation subgrade elevations,
compaction of the soils to the specifications of structural fill or overexcavation and replacement
with suitable structural fill will likely be necessary. An ESNW representative should be contacted
to confirm suitability of the foundation subgrade at the time of construction.
From a geotechnical standpoint, infiltration on the subject site should be considered infeasible to
the general sloping characteristics of the site and surrounding area. The low infiltration potential
of the native soils can result in lateral movement of shallow groundwater and would negatively
impact the regulated slopes related to the subject site and surrounding area.
Landslide and sensitive slope hazard areas are described for the subject site within the City of
Renton (COR) on-line mapping tool. ESNW recommends that qualitative slope analysis be
conducted on the subject site to determine the suitability of the landslide hazard area for slope
remediation. Final grading plans were not available at the time of this report production, and
must be provided to ESNW for the slope stability analysis at a later date.
15365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 • (425) 449-4704 • FAX (425) 449-4711
Earth Solutions NW LLC
Geotechnical Engineering, Construction
Observation/Testing and Environmental Services
Schneider Family Homes, LLC ES-9182
August 8, 2023 Executive Summary – Page 2
Earth Solutions NW, LLC
Pertinent geotechnical recommendations are provided in this study. We appreciate the
opportunity to be of service to you on this project. If you have any questions regarding the content
of this geotechnical engineering study, please call.
Sincerely,
EARTH SOLUTIONS NW, LLC
Samuel E. Suruda, L.G.
Senior Staff Geologist
Earth Solutions NW, LLC
Table of Contents
ES-9182
PAGE
INTRODUCTION ................................................................................. 1
General .................................................................................... 1
Project Description ................................................................. 1
SITE CONDITIONS ............................................................................. 2
Surface ..................................................................................... 2
Subsurface .............................................................................. 2
Topsoil and Fill ............................................................. 2
Native Soil ..................................................................... 3
Geologic Setting ........................................................... 3
Groundwater ................................................................. 3
GEOLOGIC HAZARD AREAS EVALUATION ................................... 3
Landslide Hazard .................................................................... 4
Regulated Slopes .................................................................... 4
DISCUSSION AND RECOMMENDATIONS ....................................... 5
General .................................................................................... 5
Site Preparation and Earthwork ............................................. 5
Temporary Erosion Control ......................................... 6
Stripping ....................................................................... 6
Excavations and Slopes .............................................. 6
In-situ and Imported Soil ............................................. 7
Structural Fill ................................................................ 7
Foundations ............................................................................ 8
Preliminary Seismic Design Considerations ........................ 9
Slab-on-Grade Floors ............................................................. 10
Retaining Walls ....................................................................... 10
Drainage................................................................................... 11
Preliminary Infiltration Feasibility ............................... 11
Preliminary Stormwater Vault Design ........................ 11
Preliminary Pavement Sections ............................................. 12
Utility Support and Trench Backfill ....................................... 13
LIMITATIONS ...................................................................................... 14
Additional Services ................................................................. 14
Earth Solutions NW, LLC
Table of Contents
Cont’d
ES-9182
GRAPHICS
Plate 1 Vicinity Map
Plate 2 Test Pit Location Plan
Plate 3 Retaining Wall Drainage Detail
Plate 4 Footing Drain Detail
Plate 5 Slope Fill Detail
APPENDICES
Appendix A Subsurface Exploration
Test Pit Logs
Appendix B Laboratory Test Results
Earth Solutions NW, LLC
GEOTECHNICAL ENGINEERING STUDY
PROPOSED SINGLE-FAMILY RESIDENCES
TALBOT HILLS SHORT PLAT
XXX SOUTH 55TH STREET
RENTON, WASHINGTON
ES-9182
INTRODUCTION
General
This geotechnical engineering study (study) was prepared for the proposed short plat residential
development to be constructed on 55th Street, in Renton, Washington. The purpose of this study
was to develop geotechnical recommendations for the project. The following tasks were
completed as part of our scope of services for this project:
Observation of test pits in order to characterize soil and near-surface groundwater
conditions.
Laboratory testing of soil samples collected at the test pit locations.
Engineering analyses and recommendations for the proposed development.
Preparation of this report.
The following documents and maps were reviewed as part of our report preparation:
Topographic Survey, Talbot Hills, prepared by C.E.S. NW, Inc., dated April 19, 2023.
Geologic Map of the Renton Quadrangle, King County, Washington, prepared by D.R.
Mullineaux, 1965.
Renton Municipal Code (RMC) Chapter 4-3-050 – Critical Areas Regulations.
King County Liquefaction Susceptibility Map, endorsed by the King County Flood Control
District, dated May 2010.
Online Web Soil Survey (WSS) resource, provided by the United States Department of
Agriculture (USDA), Natural Resources Conservation Service.
Project Description
We understand that four new single-family homes are proposed for the subject site. Based on
the referenced plan, maximum cuts and fills of roughly 10 feet are expected to achieve most of
the residential finish grade elevations. Infiltration is being investigated for the subject property to
accommodate runoff from new impervious surfaces related to the site improvements.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 2
Earth Solutions NW, LLC
At the time of report submission, specific building load and grading plans were not available for
review; however, we anticipate the proposed multi-family structures will be three to four stories
and constructed using relatively lightly loaded wood framing supported on a conventional
foundation system. Perimeter footing loads will likely be 2 to 4 kips per lineal foot. Slab-on-grade
loading is anticipated to be approximately 150 pounds per square foot (psf).
If the above design assumptions either change or are incorrect, ESNW should be contacted to
review the recommendations provided in this report. ESNW should review final designs to
confirm that our geotechnical recommendations have been incorporated into the plans.
SITE CONDITIONS
Surface
The subject site is located north of 55th Street, approximately 90 feet east of the intersection with
98th Avenue South, in Renton, Washington. The approximate site location is illustrated on Plate
1 (Vicinity Map). The property is comprised of a single tax parcel (King County Parcel Number
3123059119), totaling roughly 2.25 acres. Topography across the subject site generally
descends to the west, with approximately 76 feet of total elevation change present. Slope
gradients vary between gently and moderately descending slopes, with the majority of moderate
slopes concentrated in the northeastern corner of the subject site. The subject site is bordered
by South 55th Street to the south, and single-family residences to the east, west, and north.
Vegetation within the subject site consists of mature tree growth and moderate undergrowth.
Subsurface
An ESNW representative observed, logged, and sampled six test pits on April 19, 2023. The test
pits were excavated at accessible site locations, using a mini trackhoe provided by the client.
The subsurface exploration was completed to evaluate soil conditions, classify site soils, and
characterize near-surface groundwater conditions within the proposed development area. The
approximate locations of the test pits are depicted on Plate 2 (Test Pit Location Plan). Please
refer to the test pit logs provided in Appendix A for a more detailed description of subsurface
conditions. Representative soil samples collected at the test pit locations were analyzed in
general accordance with both Unified Soil Classification System (USCS) and USDA methods and
procedures.
Topsoil and Fill
Topsoil was observed to depths of generally 6 to 12 inches below the existing ground surface
(bgs). The topsoil was characterized by its dark brown color, the presence of fine organic
material, and small root intrusions.
Fill was encountered at test pit location TP-4 during our fieldwork. The fill was characterized as
a silty sand material with sparse quantities of topsoil present. The fill material was observed in a
wet condition to its terminus at a depth of approximately four and one-half feet bgs. Based on
the existing site conditions, the fill is likely related to past export activities on the subject site, and
in our opinion, is not indictive of widespread mass grading.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 3
Earth Solutions NW, LLC
Native Soil
Underlying the topsoil and fill, native soils encountered at the test pit locations were observed
primarily as medium dense to dense silty sand with varying amounts of gravel (USCS: SM and
SP-SM), consistent with the typical makeup of glacial till. In general, the native soil was
encountered in a “moist” or “wet” condition, during the time of exploration. The maximum
exploration depth was approximately nine feet bgs.
Geologic Setting
The referenced geologic map identifies kame deposits (Qit) across the subject site, with ground
moraine deposits (Qgt) present on the western property margin. The geological map identifies a
historic pebble mine on the property, located approximately in the northeastern corner of the
subject site. As described on the geologic map, Kame deposits are areas of sand and pebble
gravel in scattered terraces. Ground moraine deposits are characterized as ablation till over thick
sections of lodgment till. Till is typically comprised of unsorted cobbles, pebbly sand, and sandy
silt, with a locally compact layer (referred to as “hardpan”) at depth.
The referenced WSS resource identifies Alderwood gravelly sandy loam, 8 to 15 percent slopes,
(Map Unit Symbol: AgC) as the primary units underlying the subject site. The Alderwood series
formed in glacial till plains.
Based on the field observations, the native depositional environment is characterized as relatively
medium dense to dense glacial till, which is consistent with local geologic mapping. A pebble
and gravel surface mine was historically located on the subject site based on the referenced
geologic map. Based on our experience with kame deposits in similar depositional environments,
in our opinion, the clean sands and gravels associated with the kame deposits have been
removed from the subject site, with the remainder of the native soils being characterized as glacial
till.
Groundwater
Groundwater was not encountered during our subsurface exploration on April 19, 2023, which
were advanced to a maximum depth of about nine feet bgs. Groundwater seepage rates and
elevations fluctuate depending on many factors, including precipitation duration and intensity, the
time of year, and soil conditions. Groundwater seepage flow rates are typically higher during the
winter, spring and early summer months. Therefore, perched groundwater seepage should be
expected in site excavations, particularly if excavations are made in winter, spring and early
summer months.
GEOLOGIC HAZARD AREAS EVALUATION
ESNW reviewed both RMC 4-3-050 and available map resources (depicting geologically
hazardous areas), including the City of Renton (COR) interactive map. According to the
referenced COR Map, medium landslide hazards, and regulated and/or protected slopes are all
mapped within the subject site. The mapped hazards are largely associated with the overall
hillslope complex incorporating the subject site and surrounding area.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 4
Earth Solutions NW, LLC
Landslide Hazard
Per RMC 4-3-050G5b, landslide hazard areas can be defined as:
i. Low Landslide Hazard (LL): Areas with slopes less than 15 percent.
ii. Medium Landslide Hazard (LM): Areas with slopes between 15 percent and 40 percent,
underlain by soils that consist largely of sand, gravel, or glacial till.
iii. High Landslide Hazards (LH): Areas with slopes greater than 40 percent and areas with
slopes between 15 percent and 40 percent underlain by soils consisting largely of silt and
clay.
iv. Very High Landslide Hazards (LV): Areas of known mapped or identified landslide
deposits.
The referenced City Critical Areas Map designates a high landslide hazard on the eastern portion
of the subject site, with a moderate landslide hazard area over the remainder of the site. Based
on the referenced topographic survey, slopes on the subject site average a gradient of 60 percent.
Within the northeast corner of the site, the slope gradients average approximately 130 percent.
The areas of 130 percent slopes area a result of historical mining activities. During our visit we
did not observe surficial signs of present or recent landslides. Based on COR map, publicly
available resources provided by the Department of Natural Resources, and our site exploration,
the subject site is correctly mapped as a medium to high landslide hazard area.
Regulated Slopes
According to RMC 4-3-050G5a, steep slopes may be categorized into two types:
i. Sensitive Slopes: A hillside, or portion thereof (excluding engineering retaining walls),
characterized by:
a. An average slope of 25 percent to less than 40 percent, as identified in the City Steep
Slope Atlas or in a method approved by the City;
b. An average slope of 40 percent or greater, with a vertical rise of less than 15 feet, as
identified in the City Steep Slope Atlas or in a method approved by the City, or;
c. Abutting an average slope of 25 percent to 40 percent, as identified in the City Steep
Slope Atlas or in a method approved by the City.
ii. Protected Slopes: A hillside, or portion thereof, characterized by an average slope of 40
percent or greater grade and having a minimum vertical rise of 15 feet, as identified in the
City Steep Slope Atlas or in a method approved by the City.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 5
Earth Solutions NW, LLC
The referenced City Critical Areas Map designates the site as containing sensitive slopes. Based
on the moderately steep nature of the site gradients, it is our opinion that the designations of
sensitive and/or protected slopes on site may be impacted by the proposed project from a
geotechnical standpoint. Final grading plans were not available at the time of this report
production. ESNW recommends a qualitative slope analysis of the subject site be completed to
better evaluate the impacts of proposed short plat based on the current versus proposed site
layout. This analysis will require both the existing site survey with topographic information
included as well as a final grading plan with topography and lot layout to aid in the modeling of
the grading and surcharge conditions being proposed.
DISCUSSION AND RECOMMENDATIONS
General
Based on the results of our investigation, the construction of the proposed short plat is feasible
from a geotechnical standpoint given the results of a subsequent slope stability analysis is
completed which demonstrates adequate factors of safety for the pre- and post-development site
conditions. The primary geotechnical considerations associated with the proposed development
include the suitability of site grading and surcharge conditions resulting from re-development,
using on-site soil as structural fill, foundation support, and slab-on-grade support. ESNW
recommends that a qualitative analysis of the high landslide hazard portions of the site be
completed to assess the impacts of the proposed short plat.
In our opinion, the proposed residential structures can be supported on a conventional spread
and continuous footing system bearing on undisturbed competent native soil, compacted native
soil, or new structural fill. We anticipate competent native soil suitable for support of foundations
will be encountered at the typical footing subgrade excavation depth (roughly 18 to 24 inches
below grade). Where loose or unsuitable soil conditions are encountered at foundation subgrade
elevations, compaction of the soils to the specifications of structural fill or overexcavation and
replacement with suitable structural fill will likely be necessary. An ESNW representative should
be contacted to confirm suitability of the foundation subgrade at the time of construction.
As indicated in the Subsurface section of this report, the native soil encountered during our
fieldwork was characterized as glacial till. Based on the existing topography of the subject site
and surrounding areas, infiltration, from a geotechnical standpoint, should be considered
infeasible.
Site Preparation and Earthwork
Initial site preparation activities will consist of installing temporary erosion control measures,
establishing grading limits, performing of clearing and site stripping, and fill placement. As the
site is sloped in nature, fill placed on slopes must be placed on level benches excavated into the
existing grade. ESNW has provided a detail demonstrating the suitable approach to placement
of fill on slopes (Plate 5). Subsequent earthwork activities will involve site grading and related
infrastructure improvements.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 6
Earth Solutions NW, LLC
Temporary Erosion Control
The following TESC Best Management Practices (BMPs) are offered:
Temporary construction entrances and drive lanes, consisting of at least six inches of
quarry spalls, should be considered to both minimize off-site soil tracking and provide a
stable access entrance surface. Placing geotextile fabric underneath the quarry spalls will
provide greater stability, if needed.
Silt fencing should be placed around the construction site perimeter.
When not in use, soil stockpiles should be covered or otherwise protected.
Temporary measures for controlling surface water runoff, such as interceptor trenches,
sumps, or swales, should be installed prior to beginning earthwork activities.
Dry soils disturbed during construction should be wetted to minimize dust and airborne soil
erosion.
When appropriate, permanent planting or hydroseeding will help to stabilize on-site soil.
Additional TESC BMPs, as specified by the project civil engineer and indicated on the plans,
should be incorporated into construction activities. TESC BMPs may be modified during
construction as site conditions require and as approved by the site erosion control lead.
Stripping
Topsoil was observed to be within the upper approximately 6 to 12 inches of existing grades at
the test pit locations. Organic-rich topsoil should be stripped and segregated into a stockpile
either for later use on site or to be exported.
Excavations and Slopes
Excavation activities on site are likely to expose medium dense to dense native soil within the
upper two and one-half feet to five feet of existing grades. Based on the soil conditions observed
at the test locations, the following maximum allowable temporary slope inclinations may be used.
The applicable Federal Occupation Safety and Health Administration and Washington Industrial
Safety and Health Act soil classifications are also provided:
Areas exposing groundwater seepage 1.5H:1V (Type C)
Loose soil 1.5H:1V (Type C)
Medium dense native soil 1H:1V (Type B)
Dense to very dense “hardpan” native soil 0.75H:1V (Type A)
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 7
Earth Solutions NW, LLC
Permanent slopes should be planted with vegetation to both enhance stability and minimize
erosion and should maintain a gradient of 2H:1V or flatter. The presence of perched groundwater
may cause localized sloughing of temporary slopes. An ESNW representative should observe
temporary and permanent slopes to confirm the slope inclinations are suitable for the exposed
soil conditions and to provide additional excavation and slope recommendations, as necessary.
If the recommended temporary slope inclinations cannot be achieved, temporary shoring may be
necessary to support excavations.
In-situ and Imported Soil
The on-site soil is moisture sensitive, and successful use of the on-site soil as structural fill will
largely be dictated by the moisture content at the time of placement and compaction. Remedial
measures may be necessary as part of site grading and earthwork activities. If the on-site soil
cannot be successfully compacted, the use of an imported soil may be necessary. In our opinion,
a contingency should be provided in the project budget for the export of soil that cannot be
successfully compacted as structural fill, particularly if grading activities take place during periods
of rainfall. In general, soils with appreciable fines contents (greater than 5 percent) typically
degrade rapidly when exposed to periods of rainfall.
Imported soil intended for use as structural fill should consist of a well-graded, granular soil with
a moisture content that is at (or slightly above) the optimum level. During wet weather conditions,
imported soil intended for use as structural fill should consist of a well-graded, granular soil with
a fines content of 5 percent or less (where the fines content is defined as the percent passing the
Number 200 sieve, based on the minus three-quarter-inch fraction).
Structural Fill
Structural fill is defined as compacted soil placed in foundation, slab-on-grade, roadway,
permanent slope, retaining wall, and utility trench backfill areas. Structural fill placed and
compacted during site grading activities should meet the following specifications and guidelines:
Structural fill material Granular soil*
Moisture content At or slightly above optimum**
Relative compaction (minimum) 95 percent (Modified Proctor)
Loose lift thickness (maximum) 12 inches
* The existing soil may not be suitable for use as structural fill unless the soil is at (or slightly above) the optimum
moisture content at the time of placement and compaction.
** Soil shall not be placed dry of optimum and should be evaluated by ESNW during construction.
With respect to underground utility installations and backfill, local jurisdictions may dictate the soil
type(s) and compaction requirements. Areas of otherwise unsuitable material and debris should
be removed from structural areas and replaced with structural fill.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 8
Earth Solutions NW, LLC
Foundations
The proposed residential structures can be supported on a conventional spread and continuous
footing system bearing on undisturbed competent native soil, native soil compacted in-place, or
new structural fill. We anticipate competent native soil suitable for support of foundations will be
encountered at the typical footing subgrade excavation depth (roughly 18 to 24 inches below
grade). The exception to this general statement of subgrade suitability is where existing fill was
observed at test location TP-4 to a depth of four and one-half feet. The fill observed at TP-4 will
need to be removed and replaced to a depth below the observed topsoil at three feet. This
material should be replaced following compaction of the material left in-place following the
overexcavation of fill. Where loose or unsuitable soil conditions are encountered at foundation
subgrade elevations, compaction of the soils to the specifications of structural fill or
overexcavation and replacement with suitable structural fill will likely be necessary. An ESNW
representative should be contacted to confirm suitability of the foundation subgrade at the time
of construction.
Provided the structure will be supported as described above, the following parameters may be
used for design of the new foundations:
Allowable soil bearing capacity 2,500 psf
Passive earth pressure 300 pcf
Coefficient of friction 0.40
A one-third increase in the allowable soil bearing capacity may be assumed for short-term wind
and seismic loading conditions. The passive earth pressure and coefficient of friction values
include a safety factor of 1.5. With structural loading as expected, total settlement in the range
of one inch is anticipated, with differential settlement of about one-half inch. Most of the
anticipated settlement should occur during construction as dead loads are applied.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 9
Earth Solutions NW, LLC
Preliminary Seismic Design Considerations
The 2018 International Building Code (2018 IBC) recognizes the most recent edition of the
Minimum Design Loads for Buildings and Other Structures manual (ASCE 7-16) for seismic
design, specifically with respect to earthquake loads. Based on the soil conditions encountered
at the test pit locations, the parameters and values provided below are recommended for seismic
design per the 2018 IBC.
Parameter Value
Site Class D*
Mapped short period spectral response acceleration, SS (g) 1.385
Mapped 1-second period spectral response acceleration, S1 (g) 0.472
Short period site coefficient, Fa 1.0
Long period site coefficient, Fv 1.828**
Adjusted short period spectral response acceleration, SMS (g) 1.385
Adjusted 1-second period spectral response acceleration, SM1 (g) 0.863**
Design short period spectral response acceleration, SDS (g) 0.923
Design 1-second period spectral response acceleration, SD1 (g) 0.575**
* Assumes medium dense to dense native soil conditions, encountered to a maximum depth of nine feet bgs during
the April 2023 field exploration, remain medium dense or better to at least 100 feet bgs.
** Values assume Fv may be determined using linear interpolation per Table 11.4-2 in ASCE 7-16.
As indicated in the table footnote, several of the seismic design values provided above are
dependent on the assumption that site-specific ground motion analysis (per Section 11.4.8 of
ASCE 7-16) will not be required for the subject project. ESNW recommends the validity of this
assumption be confirmed at the earliest available opportunity during the planning and early
design stages of the project. Further discussion between the project structural engineer, the
project owner, and ESNW may be prudent to determine the possible impacts to the structural
design due to increased earthquake load requirements under the 2018 IBC. ESNW can provide
additional consulting services to aid with design efforts, including supplementary geotechnical
and geophysical investigation, upon request.
Liquefaction is a phenomenon where saturated or loose soil suddenly loses internal strength and
behaves as a fluid. This behavior is in response to increased pore water pressures resulting from
an earthquake or another intense ground shaking. In our opinion, site susceptibility to liquefaction
may be considered low. The relatively dense characteristics of the native soil and the lack of an
established, shallow groundwater table were the primary bases for this opinion.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 10
Earth Solutions NW, LLC
Slab-on-Grade Floors
Slab-on-grade floors for the proposed residential structures should be supported on firm and
unyielding subgrades. Unstable or yielding subgrade areas should be recompacted or
overexcavated and replaced with suitable structural fill prior to slab construction.
A capillary break consisting of a minimum of four inches of free-draining crushed rock or gravel
should be placed below each slab. The free-draining material should have a fines content of 5
percent or less (percent passing the Number 200 sieve, based on the minus three-quarter-inch
fraction). In areas where slab moisture is undesirable, installation of a vapor barrier below the
slab should be considered. If a vapor barrier is to be utilized, it should be a material specifically
designed for use as a vapor barrier and should be installed per manufacturer specifications.
Retaining Walls
Retaining walls must be designed to resist earth pressures and applicable surcharge loads. The
following parameters may be used for design:
Active earth pressure (unrestrained condition) 35 pcf (equivalent fluid)
At-rest earth pressure (restrained condition) 55 pcf
Traffic surcharge* (passenger vehicles) 70 psf (rectangular distribution)
Passive earth pressure 300 pcf (equivalent fluid)
Coefficient of friction 0.40
Seismic surcharge 8H psf**
* Where applicable.
** Where H equals the retained height (in feet).
The above design parameters are based on a level backfill condition and level grade at the wall
toe. Revised design values will be necessary if sloping grades are to be used above or below
retaining walls. Additional surcharge loading from adjacent foundations, sloped backfill, or other
relevant loads should be included in the retaining wall design.
Retaining walls should be backfilled with free-draining material that extends along the height of
the wall and a distance of at least 18 inches behind the wall. The upper 12 inches of the wall
backfill may consist of a less permeable soil, if desired. A perforated drainpipe should be placed
along the base of the wall and connected to an approved discharge location. A typical retaining
wall drainage detail is provided on Plate 3. If drainage is not provided, hydrostatic pressures
should be included in the wall design.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 11
Earth Solutions NW, LLC
Drainage
Based on our field observations, groundwater seepage should be anticipated within site
excavations. Temporary measures to control surface water runoff and groundwater seepage
during construction will be critical to minimizing the potential for on-site soils to degrade. ESNW
should be consulted during preliminary grading to identify areas of seepage and provide
recommendations to reduce the potential for seepage-related instability.
Finish grades must be designed to direct surface drain water away from structures and slopes.
Water must not be allowed to pond adjacent to structures or slopes. Grades adjacent to buildings
should be sloped away from the buildings at a gradient of either at least 2 percent for a horizontal
distance of 10 feet or the maximum allowed by adjacent structures. In our opinion, foundation
drains should be installed along building perimeter footings. A typical foundation drain detail is
provided on Plate 4.
Preliminary Infiltration Feasibility
As indicated in the Subsurface section of this report, the native soil encountered during our
fieldwork was characterized as glacial till. Dense, unweathered and weakly cemented glacial till,
was encountered on the subject site at depths of roughly three to six feet bgs. In our experience,
dense glacial till generally exhibits zero infiltration capacity. The unweathered glacial till
represents a confining layer of soil which adequate vertical separation from which must be
maintained for infiltrative measures to function as anticipated. The prescribed vertical separation
from the confining layer will be difficult to maintain in this instance based on the depth at which
the unweathered glacial till was observed and the mandated minimum depth of infiltrative
measures.
As stated in Geologic Hazard Areas Evaluation in the report, a large portion of the subject site is
delineated as containing sensitive slopes. An increase in the volumes of stormwater infiltrating
into the subsurface on the subject site could result in slope destabilization.
In our opinion, the subject site should be considered infeasible for infiltration. Due to the presence
of unweathered glacial till, infiltration on the subject site would be limited to low-flow infiltration
systems. Any infiltration on the subject site has the potential to negatively impact the sensitive
slopes present on site. We recommend that no infiltration be pursued for the subject site, in our
opinion, any infiltration system has the potential to result in lateral movement of infiltrated water,
and negatively impact the subject site and downslope properties.
Preliminary Stormwater Vault Design
We understand a stormwater vault is under consideration for on-site stormwater management.
Vault foundations should be supported on competent native soil or crushed rock placed atop
competent native soil. Final stormwater vault designs must incorporate adequate buffer space
from property boundaries such that temporary excavations to construct the vault structure can be
successfully completed. Perimeter drains should be installed around the vault and conveyed to
an approved discharge point. The presence of perched groundwater seepage should be
anticipated during excavation activities for the vault.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 12
Earth Solutions NW, LLC
The following parameters can be used for stormwater vault design:
Allowable soil bearing capacity (dense native soil) 5,000 psf
Active earth pressure (unrestrained) 35 pcf
Active earth pressure (unrestrained, hydrostatic) 80 pcf
At-rest earth pressure (restrained) 55 pcf
At-rest earth pressure (restrained, hydrostatic) 100 pcf
Coefficient of friction 0.40
Passive earth pressure 300 pcf
Seismic surcharge 8H*
* Where H equals the retained height.
Retaining walls should be backfilled with free-draining material or suitable sheet drainage that
extends along the height of the walls. The upper one foot of the wall backfill can consist of a less
permeable soil, if desired. A perforated drain pipe should be placed along the base of the wall
and connected to an approved discharge location. If the elevation of the vault bottom is such that
gravity flow to an outlet is not possible, the portion of the vault below the drain should be designed
to include hydrostatic pressure. Design values accounting for hydrostatic pressure are included
above. The above passive earth pressure and coefficient of friction values include a safety factor
of 1.5.
ESNW should observe grading operations for the vault and the subgrade conditions prior to
concrete forming and pouring to confirm conditions are as anticipated, and to provide
supplemental recommendations as necessary. Additionally, ESNW should be contacted to
review final vault designs to confirm that appropriate geotechnical parameters have been
incorporated.
Preliminary Pavement Sections
The performance of site pavements is largely related to the condition of the underlying subgrade.
To ensure adequate pavement performance, the subgrade should be in a firm and unyielding
condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement
areas should be compacted to the specifications previously detailed in this report. Soft, wet, or
otherwise unsuitable subgrade areas may still exist after base grading activities. Areas
containing unsuitable or yielding subgrade conditions will require remedial measures, such as
overexcavation and/or placement of thicker crushed rock or structural fill sections, prior to
pavement.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 13
Earth Solutions NW, LLC
We anticipate new pavement sections will be subjected primarily to passenger vehicle traffic. For
lightly loaded pavement areas subjected primarily to passenger vehicles, the following
preliminary pavement sections may be considered:
A minimum of two inches of hot-mix asphalt (HMA) placed over four inches of crushed
rock base (CRB).
A minimum of two inches of HMA placed over three inches of asphalt-treated base (ATB).
Heavier traffic areas generally require thicker pavement sections depending on site usage,
pavement life expectancy, and site traffic. For preliminary design purposes, the following
pavement sections for occasional truck traffic and access roadways may be considered:
Three inches of HMA placed over six inches of CRB, or;
Three inches of HMA placed over four and one-half inches of ATB.
The HMA, ATB, and CRB materials should conform to WSDOT and/or City of Renton
specifications. All soil base material should be compacted to a relative compaction of 95 percent,
based on the laboratory maximum dry density as determined by ASTM D1557. Final pavement
design recommendations, including recommendations for heavy traffic areas, access roads, and
frontage improvement areas, can be provided once final traffic loading has been determined.
Road standards utilized by the City of Renton may supersede the recommendations provided in
this report.
If an inverted crown will be used for roadway surfaces, drainage measures should be included in
the design to prevent accumulation of water in the subgrade adjacent to catch basins. Such
measures should consist of finger drains extending from the catch basins.
Utility Support and Trench Backfill
In our opinion, the on-site soil will generally be suitable for support of utilities. Remedial measures
may be necessary in some areas to provide support for utilities, such as overexcavation and
replacement with structural fill or placement of geotextile fabric. Groundwater seepage may be
encountered within utility excavations, and caving of trench walls may occur where groundwater
or unsuitable fill are encountered. Depending on the time of year and conditions encountered,
dewatering or temporary trench shoring may be necessary during utility excavation and
installation.
The on-site soil may not be suitable for use as structural backfill throughout utility trench
excavations unless the soil is at (or slightly above) the optimum moisture content at the time of
placement and compaction. Moisture conditioning of the soil may be necessary at some locations
prior to use as structural fill. Each section of the utility lines must be adequately supported in the
bedding material. Utility trench backfill should be placed and compacted to the structural fill
specifications previously detailed in this report or to the applicable specifications of the presiding
jurisdiction.
Schneider Family Homes, LLC ES-9182
August 8, 2023 Page 14
Earth Solutions NW, LLC
LIMITATIONS
This study has been prepared for the exclusive use of Schneider Family Homes, LLC, and their
representatives. The recommendations and conclusions provided in this study are professional
opinions consistent with the level of care and skill that is typical of other members in the
profession currently practicing under similar conditions in this area. No warranty, express or
implied, is made. Variations in the subsurface conditions observed at the test pit locations may
exist and may not become evident until construction. ESNW should reevaluate the conclusions
provided in this study if variations are encountered.
Additional Services
ESNW should have an opportunity to review the final design with respect to the geotechnical
recommendations provided in this report. ESNW should also be retained to provide testing and
consultation services during construction.
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Drawn MRS
Checked SES Date May 2023
Date 05/15/2023 Proj.No.9182
Plate 1
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
Vicinity Map
Talbot Hills Short Plat
Renton,Washington
Reference:
King County,Washington
OpenStreetMap.org
NORTH
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
SITE
Renton
Kent
Plate
Proj.No.
Date
Checked
Drawn
Earth
Solutions
NWLLC
Geotechnical
Engineering,
Construction
Observation/Testing
and
Environmental
Services
Earth
Solutions
NWLLC
Earth
Solutions
NW
LLC
MRS
SES
05/12/2023
9182
2
Test
Pit
Location
Plan
Talbot
Hills
Short
Plat
Renton,
Washington
NORTH
NOT -TO -SCALE
NOTE:This plate may contain areas of color.ESNW cannot be
responsible for any subsequent misinterpretation of the information
resulting from black &white reproductions of this plate.
NOTE:The graphics shown on this plate are not intended for design
purposes or precise scale measurements,but only to illustrate the
approximate test locations relative to the approximate locations of
existing and /or proposed site features.The information illustrated
is largely based on data provided by the client at the time of our
study.ESNW cannot be responsible for subsequent design changes
or interpretation of the data by others.
LEGEND
Approximate Location of
ESNW Test Pit,Proj.No.
ES-9182,April 2023
Subject Site
Existing Building
TP-1
TP-1
TP-2
TP-3
TP-4
TP-5
TP-6
270
280
290
260
250240
230
270 280 290
260250240230
220
220
S.55TH STREET
S.
55TH
STREET
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Drawn MRS
Checked SES Date May 2023
Date 05/14/2023 Proj.No.9182
Plate 3
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
NOTES:
Free-draining Backfill should consist
of soil having less than 5 percent fines.
Percent passing No.4 sieve should be
25 to 75 percent.
Sheet Drain may be feasible in lieu
of Free-draining Backfill,per ESNW
recommendations.
Drain Pipe should consist of perforated,
rigid PVC Pipe surrounded with 1-inch
Drain Rock.
LEGEND:
Free-draining Structural Backfill
1-inch Drain Rock
18"Min.
Structural
Fill
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
SCHEMATIC ONLY -NOT TO SCALE
NOT A CONSTRUCTION DRAW ING
Retaining Wall Drainage Detail
Talbot Hills Short Plat
Renton,Washington
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Drawn MRS
Checked SES Date May 2023
Date 05/14/2023 Proj.No.9182
Plate 4
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
Slope
Perforated Rigid Drain Pipe
(Surround in Drain Rock)
18"Min.
NOTES:
Do NOT tie roof downspouts
to Footing Drain.
Surface Seal to consist of
12"of less permeable,suitable
soil.Slope away from building.
LEGEND:
Surface Seal:native soil or
other low-permeability material.
1-inch Drain Rock
SCHEMATIC ONLY -NOT TO SCALE
NOT A CONSTRUCTION DRAW ING
Footing Drain Detail
Talbot Hills Short Plat
Renton,Washington
Drawn CAM
Checked SHA Date June 2023
Date 06/15/2023 Proj.No.9182
Plate 5
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
Earth Solutions NWLLCEarthSolutionsNWLLC
EarthSolutions
NW LLC
SCHEMATIC ONLY -NOT TO SCALE
NOT A CONSTRUCTION DRAW ING
NOTES:
Slope should be stripped of topsoil and
unsuitable materials prior to excavating
Keyway or benches.
Benches will typically be equal to a bulldozer
blade width of approximately 8 feet but
shall be at least 4 feet.
Final slope gradient should be 2H :1V.
Final slope face should be densified by
over-building with compacted fill and
trimming back to shape or by compaction
with a bulldozer or vibratory drum roller.
Planting or hydroseeding slope face with
a rapid growth deep-rooted vegetative mat
will reduce erosion potential of slope area.
Use of pegged-in-place jute matting or
geotechnical fabric will help maintain the
seed and mulch in place until the root
system has an opportunity to germinate.
Structural fill should be placed in thin loose
lifts not exceeding 12 inches in thickness.
Each lift should be compacted to no less than
the degree specified in the “Site Preparation
and Earthwork”section of this report.No
additional lift should be placed until compaction
is achieved.
2
1
Final Slope
Gradient
Compacted Slope Face
Existing Grade
Typical “Bench”
Keyed into Existing Slope Face
(Geotechnical Engineer to Confirm)
“Key”
(Minimum 2'Deep by 6'W ide)
Bench and Keyway Fill to
consist of suitable granular
material approved by the
Geotechnical Engineer
Drainage measures (blanket drain,toe drain,
bench drain,etc.)may be necessary as
recommended by the Geotechnical
Engineer during construction
Slope Fill Detail
Talbot Hills Short Plat
Renton,Washington
Earth Solutions NW, LLC
Appendix A
Subsurface Exploration
Test Pit Logs
ES-9182
Subsurface conditions at the subject site were explored on April 19, 2023. Six test pits were
excavated using a mini-trackhoe and operator provided by the client. The approximate locations
of the test pits are illustrated on Plate 2 of this study. The test pit logs are provided in this
Appendix. The maximum exploration depth was approximately nine feet bgs.
The final logs represent the interpretations of the field logs and the results of laboratory analyses.
The stratification lines on the logs represent the approximate boundaries between soil types. In
actuality, the transitions may be more gradual.
>
12%
Fines
<
5%
Fines
Highly
Organic
Soils
Silts
and
Clays
Liquid
Limit
50
or
More
Silts
and
Clays
Liquid
Limit
Less
Than
50
Fine-Grained
Soils
-
50%
or
More
Passes
No.
200
Sieve
Coarse-Grained
Soils
-
More
Than
50%
Retained
on
No.
200
Sieve
Sands
-
50%
or
More
of
Coarse
Fraction
Passes
No.
4
Sieve
Gravels
-
More
Than
50%
of
Coarse
Fraction
Retained
on
No.
4
Sieve
>
12%
Fines
<
5%
Fines GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MH
CH
OH
PT
Well-graded gravel with
or without sand,little to
no fines
Poorly graded gravel with
or without sand,little to
no fines
Silty gravel with or without
sand
Clayey gravel with or
without sand
Well-graded sand with
or without gravel,little to
no fines
Poorly graded sand with
or without gravel,little to
no fines
Silty sand with or without
gravel
Clayey sand with or
without gravel
Silt with or without sand
or gravel;sandy or
gravelly silt
Clay of low to medium
plasticity;lean clay with
or without sand or gravel;
sandy or gravelly lean clay
Organic clay or silt of
low plasticity
Elastic silt with or without
sand or gravel;sandy or
gravelly elastic silt
Clay of high plasticity;
fat clay with or without
sand or gravel;sandy or
gravelly fat clay
Organic clay or silt of
medium to high plasticity
Peat,muck,and other
highly organic soils
EEaarrtthh SSoolluuttiioonnss NNWW LLC
Geotechnical Engineering,Construction
Observation/Testing and Environmental Services
EXPLORATION LOG KEY
Fill FILL Made Ground
Classifications of soils in this geotechnical report and as shown on the exploration logs are based on visual
field and/or laboratory observations,which include density/consistency,moisture condition,grain size,and
plasticity estimates,and should not be construed to imply field or laboratory testing unless presented herein.
Visual-manual and/or laboratory classification methods of ASTM D2487 and D2488 were used as an
identification guide for the Unified Soil Classification System.
Terms Describing Relative Density and Consistency
Coarse-Grained Soils:
Fine-Grained Soils:
SPT blows/foot
SPT blows/foot
Test Symbols &Units
Fines =Fines Content (%)
MC =Moisture Content (%)
DD =Dry Density (pcf)
Str =Shear Strength (tsf)
PID =Photoionization Detector (ppm)
OC =Organic Content (%)
CEC =Cation Exchange Capacity (meq/100 g)
LL =Liquid Limit (%)
PL =Plastic Limit (%)
PI =Plasticity Index (%)
Component Definitions
Descriptive Term Size Range and Sieve Number
Smaller than No.200 (0.075 mm)
Boulders
Modifier Definitions
Percentage by
Weight (Approx.)
<5
5 to 14
15 to 29
>30_
Modifier
Trace (sand,silt,clay,gravel)
Slightly (sandy,silty,clayey,gravelly)
Sandy,silty,clayey,gravelly
Very (sandy,silty,clayey,gravelly)
Moisture Content
Dry -Absence of moisture,dusty,dry to
the touch
Damp -Perceptible moisture,likely below
optimum MC
Moist -Damp but no visible water,likely
at/near optimum MC
Wet -Water visible but not free draining,
likely above optimum MC
Saturated/Water Bearing -Visible free
water,typically below groundwater table
Symbols
Cement grout
surface seal
Bentonite
chips
Grout
seal
Filter pack with
blank casing
section
Screened casing
or Hydrotip with
filter pack
End cap
ATD =At time
of drilling
Static water
level (date)
_>50
Density
Very Loose
Loose
Medium Dense
Dense
Very Dense
Consistency
Very Soft
Soft
Medium Stiff
Stiff
Very Stiff
Hard
<4
4 to 9
10 to 29
30 to 49
<2
2 to 3
4 to 7
8 to 14
15 to 29
_>30
LLC
EarthSolutions
NW LLC
Cobbles
Gravel
Coarse Gravel
Fine Gravel
Sand
Coarse Sand
Medium Sand
Fine Sand
Silt and Clay
Larger than 12"
3"to 12"
3"to No.4 (4.75 mm)
3"to 3/4"
3/4"to No.4 (4.75 mm)
No.4 (4.75 mm)to No.200 (0.075 mm)
No.4 (4.75 mm)to No.10 (2.00 mm)
No.10 (2.00 mm)to No.40 (0.425 mm)
No.40 (0.425 mm)to No.200 (0.075 mm)
MC = 15.9
MC = 10.0
MC = 13.8
MC = 16.0
Fines = 45.4
TPSL
SM
Dark brown TOPSOIL, root intrusions to 2'
Brown silty SAND, medium dense, moist
-becomes gray, damp
[USDA Classification: slightly gravelly fine sandy LOAM]
Test pit terminated at 8.5 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
LIMITATIONS: Ground elevation (if listed) is approximate; the test location was not surveyed.
Coordinates are approximate and based on the WGS84 datum. Do not rely on this test log as a
standalone document. Refer to the text of the geotechnical report for a complete understanding
of subsurface conditions.
1.0
8.5
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
PAGE 1 OF 1
TEST PIT NUMBER TP-1
EXCAVATION CONTRACTOR Client Provided
DATE STARTED 4/19/23 COMPLETED 4/19/23
GROUND WATER LEVEL:
GROUND ELEVATION
LATITUDE 47.43044 LONGITUDE -122.2092
LOGGED BY SES CHECKED BY SHA
NOTES
SURFACE CONDITIONS Duff
AT TIME OF EXCAVATIONAT TIME OF EXCAVATION
AFTER EXCAVATION
PROJECT NUMBER ES-9182 PROJECT NAME Talbot Hills Short Plat
GE
N
E
R
A
L
B
H
/
T
P
/
W
E
L
L
-
9
1
8
2
.
G
P
J
-
G
I
N
T
U
S
.
G
D
T
-
8
/
8
/
2
3
Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.
S
.
C
.
S
.
MATERIAL DESCRIPTION
GR
A
P
H
I
C
LO
G
MC = 8.9
Fines = 9.6
MC = 15.2
MC = 15.4
TPSL
SP-
SM
SM
Dark brown TOPSOIL, root intrusions to 3'
Brown poorly graded SAND with silt and gravel, medium dense, damp
[USDA Classification: very gravelly loamy SAND]
Gray silty SAND with gravel, dense, damp
-weakly cemented
Test pit terminated at 7.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
LIMITATIONS: Ground elevation (if listed) is approximate; the test location was not surveyed.
Coordinates are approximate and based on the WGS84 datum. Do not rely on this test log as a
standalone document. Refer to the text of the geotechnical report for a complete understanding
of subsurface conditions.
0.5
4.0
7.0
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
PAGE 1 OF 1
TEST PIT NUMBER TP-2
EXCAVATION CONTRACTOR Client Provided
DATE STARTED 4/19/23 COMPLETED 4/19/23
GROUND WATER LEVEL:
GROUND ELEVATION
LATITUDE 47.43079 LONGITUDE -122.20919
LOGGED BY SES CHECKED BY SHA
NOTES
SURFACE CONDITIONS Duff
AT TIME OF EXCAVATIONAT TIME OF EXCAVATION
AFTER EXCAVATION
PROJECT NUMBER ES-9182 PROJECT NAME Talbot Hills Short Plat
GE
N
E
R
A
L
B
H
/
T
P
/
W
E
L
L
-
9
1
8
2
.
G
P
J
-
G
I
N
T
U
S
.
G
D
T
-
8
/
8
/
2
3
Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.
S
.
C
.
S
.
MATERIAL DESCRIPTION
GR
A
P
H
I
C
LO
G
MC = 15.3
MC = 12.7
TPSL
SM
Dark brown TOPSOIL
Brown silty SAND, medium dense, damp
-becomes gray, dense
-weakly cemented
Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
LIMITATIONS: Ground elevation (if listed) is approximate; the test location was not surveyed.
Coordinates are approximate and based on the WGS84 datum. Do not rely on this test log as a
standalone document. Refer to the text of the geotechnical report for a complete understanding
of subsurface conditions.
1.0
8.0
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
PAGE 1 OF 1
TEST PIT NUMBER TP-3
EXCAVATION CONTRACTOR Client Provided
DATE STARTED 4/19/23 COMPLETED 4/19/23
GROUND WATER LEVEL:
GROUND ELEVATION
LATITUDE 47.43052 LONGITUDE -122.20957
LOGGED BY SES CHECKED BY SHA
NOTES
SURFACE CONDITIONS Duff
AT TIME OF EXCAVATIONAT TIME OF EXCAVATION
AFTER EXCAVATION
PROJECT NUMBER ES-9182 PROJECT NAME Talbot Hills Short Plat
GE
N
E
R
A
L
B
H
/
T
P
/
W
E
L
L
-
9
1
8
2
.
G
P
J
-
G
I
N
T
U
S
.
G
D
T
-
8
/
8
/
2
3
Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.
S
.
C
.
S
.
MATERIAL DESCRIPTION
GR
A
P
H
I
C
LO
G
MC = 21.1
MC = 16.0
Fines = 34.8
MC = 19.1
SM
SM
Brown silty SAND with gravel, medium dense, wet (Fill)
-sparse topsoil in mixture
Brown silty SAND with gravel, dense, moist
-weakly cemented
[USDA Classification: gravelly fine sandy LOAM]
-becomes gray, very dense
Test pit terminated at 9.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
LIMITATIONS: Ground elevation (if listed) is approximate; the test location was not surveyed.
Coordinates are approximate and based on the WGS84 datum. Do not rely on this test log as a
standalone document. Refer to the text of the geotechnical report for a complete understanding
of subsurface conditions.
4.5
9.0
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
PAGE 1 OF 1
TEST PIT NUMBER TP-4
EXCAVATION CONTRACTOR Client Provided
DATE STARTED 4/19/23 COMPLETED 4/19/23
GROUND WATER LEVEL:
GROUND ELEVATION
LATITUDE 47.43093 LONGITUDE -122.20975
LOGGED BY SES CHECKED BY SHA
NOTES
SURFACE CONDITIONS Duff/fill
AT TIME OF EXCAVATIONAT TIME OF EXCAVATION
AFTER EXCAVATION
PROJECT NUMBER ES-9182 PROJECT NAME Talbot Hills Short Plat
GE
N
E
R
A
L
B
H
/
T
P
/
W
E
L
L
-
9
1
8
2
.
G
P
J
-
G
I
N
T
U
S
.
G
D
T
-
8
/
8
/
2
3
Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.
S
.
C
.
S
.
MATERIAL DESCRIPTION
GR
A
P
H
I
C
LO
G
MC = 13.6
MC = 17.0
Fines = 44.9
TPSL
SM
Dark brown TOPSOIL, minimal root intrusions
Brown silty SAND with gravel, medium dense, moist
-becomes dense to very dense
[USDA Classification: slightly gravelly fine sandy LOAM]
Test pit terminated at 7.5 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
LIMITATIONS: Ground elevation (if listed) is approximate; the test location was not surveyed.
Coordinates are approximate and based on the WGS84 datum. Do not rely on this test log as a
standalone document. Refer to the text of the geotechnical report for a complete understanding
of subsurface conditions.
0.5
7.5
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
PAGE 1 OF 1
TEST PIT NUMBER TP-5
EXCAVATION CONTRACTOR Client Provided
DATE STARTED 4/19/23 COMPLETED 4/19/23
GROUND WATER LEVEL:
GROUND ELEVATION
LATITUDE 47.43078 LONGITUDE -122.2099
LOGGED BY SES CHECKED BY SHA
NOTES
SURFACE CONDITIONS Duff
AT TIME OF EXCAVATIONAT TIME OF EXCAVATION
AFTER EXCAVATION
PROJECT NUMBER ES-9182 PROJECT NAME Talbot Hills Short Plat
GE
N
E
R
A
L
B
H
/
T
P
/
W
E
L
L
-
9
1
8
2
.
G
P
J
-
G
I
N
T
U
S
.
G
D
T
-
8
/
8
/
2
3
Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.
S
.
C
.
S
.
MATERIAL DESCRIPTION
GR
A
P
H
I
C
LO
G
MC = 14.5
MC = 15.8
MC = 14.2
TPSL
SM
Dark brown TOPSOIL, minimal root intrusions
Brown silty SAND, medium dense, moist
Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during
excavation. No caving observed.
LIMITATIONS: Ground elevation (if listed) is approximate; the test location was not surveyed.
Coordinates are approximate and based on the WGS84 datum. Do not rely on this test log as a
standalone document. Refer to the text of the geotechnical report for a complete understanding
of subsurface conditions.
0.5
8.0
SA
M
P
L
E
T
Y
P
E
NU
M
B
E
R
DE
P
T
H
(f
t
)
0.0
2.5
5.0
7.5
PAGE 1 OF 1
TEST PIT NUMBER TP-6
EXCAVATION CONTRACTOR Client Provided
DATE STARTED 4/19/23 COMPLETED 4/19/23
GROUND WATER LEVEL:
GROUND ELEVATION
LATITUDE 47.43051 LONGITUDE -122.20992
LOGGED BY SES CHECKED BY SHA
NOTES
SURFACE CONDITIONS Duff
AT TIME OF EXCAVATIONAT TIME OF EXCAVATION
AFTER EXCAVATION
PROJECT NUMBER ES-9182 PROJECT NAME Talbot Hills Short Plat
GE
N
E
R
A
L
B
H
/
T
P
/
W
E
L
L
-
9
1
8
2
.
G
P
J
-
G
I
N
T
U
S
.
G
D
T
-
8
/
8
/
2
3
Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
TESTS
U.
S
.
C
.
S
.
MATERIAL DESCRIPTION
GR
A
P
H
I
C
LO
G
Earth Solutions NW, LLC
Appendix B
Laboratory Test Results
ES-9182
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
0.0010.010.1110100
3
D100
140
Specimen Identification
1
fine
6
HYDROMETER
304
45.4
9.6
34.8
44.9
101/2
COBBLES
Specimen Identification
4
coarse
20 401.5 8 14
USDA: Gray Slightly Gravelly Fine Sandy Loam. USCS: SM.
USDA: Brown Very Gravelly Loamy Sand. USCS: SP-SM with Gravel.
USDA: Gray Gravelly Fine Sandy Loam. USCS: SM with Gravel.
USDA: Brown Slightly Gravelly Fine Sandy Loam. USCS: SM.
6 60
PE
R
C
E
N
T
F
I
N
E
R
B
Y
W
E
I
G
H
T
D10
0.331
0.169
7.171
0.296
0.178
GRAIN SIZE DISTRIBUTION
100
91.19
LL
TP-01
TP-02
TP-04
TP-05
0.079
3/4
U.S. SIEVE OPENING IN INCHES U.S. SIEVE NUMBERS
GRAVEL SAND
19
37.5
37.5
19
%Silt
0.19
TP-01
TP-02
TP-04
TP-05
2 2003
Cc CuClassification
%Clay
16
PID60 D30
coarse SILT OR CLAYfinemedium
GRAIN SIZE IN MILLIMETERS
3/8 50
8.5ft.
2.0ft.
6.0ft.
6.0ft.
8.50ft.
2.00ft.
6.00ft.
6.00ft.
PL
PROJECT NUMBER ES-9182 PROJECT NAME Talbot Hills Short Plat
GR
A
I
N
S
I
Z
E
U
S
D
A
E
S
-
9
1
8
2
T
A
L
B
O
T
H
I
L
L
S
S
H
O
R
T
P
L
A
T
.
G
P
J
G
I
N
T
U
S
L
A
B
.
G
D
T
5
/
4
/
2
3
Earth Solutions NW, LLC
15365 N.E. 90th Street, Suite 100
Redmond, Washington 98052
Telephone: 425-449-4704
Fax: 425-449-4711
Earth Solutions NW, LLC
Report Distribution
ES-9182
Schneider Family Homes, LLC
Attention: Zach Schneider