REVIEWED PLN BLD2023-1300+GEO REPORT+10.18.2023_2.09.23_PM+3848255RECEIVED
Oct 27 2023
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
BLD2023-1300
....,...,.
REVIEWED
BY
CITY OF EDMONDS
BUILDING DEPARTMENT;
- - - - - - - - - - - - -
Reviewed by
City of Edmonds ;
Planning Division '
'---------------
MP ENGINEERING
PROPOSED RESIDENTIAL DEVELOPMENT
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9222 183RD PL SW
EDMONDS, WASHINGTON
OCTOBER 6, 2023
MP ENGINEERING, PLLC
MPGEOTECH.COM
11900 NE 1ST ST SUITE 300, BELLEVUE, WA 98005
TABLE OF CONTENTS
1.0 SUMMARY.....................................................................................................................................................1
2.0 SITE AND PROJECT DESCRIPTION.................................................................................................................
3
3.0 SUBSURFACE EXPLORATIONS.......................................................................................................................
4
3.1 EXPLORATORY METHODS................................................................................................................................
4
3.2 SITE GEOLOGY..................................................................................................................................................
5
3.3 SOIL CONDITIONS............................................................................................................................................
6
3.4 GROUNDWATER CONDITIONS.........................................................................................................................
6
3.5 SUBSURFACE CONTAMINATION......................................................................................................................
7
4.0 ENVIRONMENTALLY CRITICAL AREAS CONSIDERATIONS............................................................................
7
4.1 EROSION HAZARDS..........................................................................................................................................
7
4.2 LANDSLIDE HAZARD AREAS.............................................................................................................................
9
5.0 CONCLUSIONS AND RECOMMENDATIONS................................................................................................
10
5.1 SITE PREPARATION........................................................................................................................................
10
5.2 EXCAVATION AND SLOPES.............................................................................................................................
11
5.3 SEISMIC DESIGN PARAMETERS......................................................................................................................
13
5.4 LIQUEFACTION POTENTIAL............................................................................................................................
14
5.5 BUILDING FOUNDATIONS..............................................................................................................................
14
5.6 SLAB -ON -GRADE FLOORS..............................................................................................................................
15
5.7 DRAINAGE SYSTEMS......................................................................................................................................
16
5.8 SITE UTILITIES................................................................................................................................................
17
5.9 STRUCTURAL FILL...........................................................................................................................................
18
6.0 ADDITIONAL SERVICES................................................................................................................................
20
7.0 CLOSURE......................................................................................................................................................20
ATTACHMENTS:
Figure 1 Vicinity Map
Figure 2 Site and Exploration Plan
Appendix A Field Exploration Procedures and Logs
Appendix B Laboratory Testing Procedures and Results
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GEOTECHNICAL ENGINEERING STUDY
PROPOSED RESIDENTIAL DEVELOPMENT
PARCEL NO. 00588200000300
EDMONDS, WASHINGTON 98020
PROJECT NO. 23-0104
1.0 SUMMARY
The following summary of project geotechnical considerations is presented for introductory purposes,
and as such, should be used only in conjunction with the full text of this report.
• Project Description: The subject site is located at 9222 183RD PL SW, Edmonds, Washington. The
property consists of one tax parcel (Snohomish County Parcel No. 00588200000300) spanning
approximately 0.27 acres. Our understanding is that the proposed development entails the
construction of a new front deck, a covered back patio, and renovations to the first floor and
basement of the existing SFR.
• Exploratory Methods: MPE explored subsurface conditions on September 23, 2023 by three test
pits advanced at strategic locations across the project site to a depth up to 9 feet below existing
grade.
• Site Conditions: The site gently slopes downward from southeast to northwest, transitioning from
an elevation of 220 to 205 feet. The site is bordered by 183rd PL SW to the north and residential
dwellings to the south, east, and west.
• Soil Conditions: The soils encountered during our investigation consist mainly of Glacial Drift
deposits, along with a top layer of Topsoil/Fill, measuring up to 4.0 feet thick. Our geotechnical
laboratory tests revealed moisture content variations in the Glacial Drift soils during exploration,
ranging from 13 to 17 percent. Furthermore, the fines content, determined by the percentage
passing the U.S. No. 200 screen, ranged from 11 to 15 percent.
• Groundwater Conditions: Groundwater seepage was not encountered during our investigation
on September 23, 2023. However, it should be noted that perched groundwater can occur atop
dense silty sand soils as downward percolation of groundwater is inhibited by the less permeable
soils. Groundwater levels may fluctuate throughout the year in response to precipitation patterns,
on- or off -site construction, irrigation activities, and site utilization.
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• Environmentally Critical Areas (ECA) Considerations: As part of our study, we conducted a
comprehensive review of potential geologic hazards at the subject site, as outlined in the City of
Edmonds Community Development Code (ECDC) Chapter 23.80, 'Geologically Hazardous Areas',
in alignment with the Critical Areas Determination (CRA2023-0089) letter dated June 8, 2023.
Both Erosion Hazard Areas and Landslide Hazard Areas were assessed in accordance with ECDC
Chapter 23.80.020. Concerning Erosion Hazard Areas, our evaluation of the NRCS Soil Survey
indicates that the property falls under the category of Alderwood gravelly sandy loam with slopes
ranging from 15 to 30 percent, aligning with erosion hazard criteria. Despite the absence of
construction near or on these slopes, erosion mitigation recommendations are provided in
Section 4.1 of this report. By following these recommendations, we anticipate that the project
will not contribute to increased surface water discharge, sedimentation, compromised slope
stability on adjacent properties, or adverse effects on critical areas. These measures include silt
fencing installation, strategic construction scheduling, mulching, interceptor swales, and
responsible stormwater management to prevent sediment transport.
Regarding Landslide Hazard Areas, our comprehensive site reconnaissance and soil analysis
revealed no signs of historical slope instability or soils consistent with landslide deposits. The
site's underlying native soils comprise robust Glacial Drift deposits, without apparent planes of
weakness or preferential failure surfaces. Importantly, the site's proximity to watercourses or
water bodies, which could potentially lead to erosion or slope undercutting, was absent.
Throughout the exploration on September 23, 2023, groundwater was not encountered. After a
meticulous review of these site conditions, we hold the opinion that the proposed construction
will not escalate geological hazard risks to neighboring properties beyond pre -development
conditions, nor will it adversely affect other critical areas. Therefore, in our professional judgment,
the development can be securely integrated into the site and does not fall within ECDC's
definition of a Landslide Hazard Area.
• Foundations: Conventional spread footings could be supported either on adequately compacted
structural fill directly over the undisturbed Glacial Drift deposits or on the undisturbed dense
Glacial Drift deposits, with maximum allowable pressures of 2,000 psf or 2,500 psf, respectively.
• On -site Soil Considerations: The majority of on -site soils exhibit high sensitivity to moisture,
making them prone to disturbance when wet. The contractor should implement suitable
temporary drainage systems at the construction site and minimize traffic over exposed subgrades.
Ideally, scheduling earthwork during the summer and fall months, when drier weather prevails,
will optimize the feasibility of reusing on -site soils. Additionally, these seasons coincide with
lower groundwater levels, further aiding construction efforts.
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2.0 SITE AND PROJECT DESCRIPTION
The subject site is located at 9222 183RD PL SW, Edmonds, Washington, as depicted in Figure 1, Vicinity
Map. The property comprises a single tax parcel (Snohomish County Parcel No. 00588200000300),
covering approximately 0.27 acres. The site is bordered by 183rd PL SW to the north and residential
dwellings to the south, east, and west. The driveway section of the lot is mostly level, gradually ascending
toward the subject single-family residence (SFR). The overall site gently slopes downward from southeast
to northwest, transitioning from an elevation of 220 to 205 feet. Please refer to Figure 2, attached
herewith, for an illustration of the site layout. Currently, the site features an SFR, and an overview of the
site conditions is presented in Images 1 and 2. Our understanding is that the proposed development
entails the construction of a new front deck, a covered back patio, and renovations to the first floor and
basement of the existing SFR.
The conclusions and recommendations contained in this report are based on our understanding of the
currently proposed utilization of the project site, as derived from preliminary layout drawings, written
information, and verbal information supplied to us. It is important to note that any alterations to the
current project proposal may necessitate adjustments to the conclusions and recommendations outlined
in this report.
Image 1. Overall view from northwest to southeast.
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Image 2. Overall view of the backyard from northeast to southwest.
3.0 SUBSURFACE EXPLORATIONS
3.1 EXPLORATORY METHODS
We explored surface and subsurface conditions at the project site on September 23, 2023. Our study
included the following:
• A visual surface reconnaissance of the site;
• A review of published geologic and seismologic maps and literature,
• Three test pits (designated TP-01 through TP-03) advanced at strategic locations across the site;
and
• Three grain -size analysis and Three moisture content performed on selected soil samples
obtained from strategic locations beneath the site.
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Table 1 summarizes the approximate functional locations, surface elevations, and termination depths of
our explorations, and Figure 2 depicts their approximate relative locations. Appendix A of this report
describes our field explorations procedures, and Appendix B describes our laboratory testing procedures.
It should be realized that the explorations utilized for this evaluation reveal subsurface conditions only
at discrete locations across the project site and that actual conditions in other areas could vary. In
addition, the nature and extent of any such variations would not become evident until additional
explorations are performed or until construction activities have begun. If significant variations are
observed at that time, we may need to modify our conclusions and recommendations contained in this
report to reflect the actual site conditions.
Table 1. Approximate Locations, Elevations, and Depths of Explorations.
Exploration I Functional Location I Surface Elevation Termination Depth
TP-01 North of the site 210 9
TP-02 South of the site 218 9
TP-03 Mid -point of the site 1 213 9
(East of the Covered Patio)
Elevation datum: Preliminary site plan provided by Yen Design, Inc.
3.2 SITE GEOLOGY
General geologic information for the project area was obtained by reviewing the Geologic map of the
Edmonds East and part of the Edmonds West quadrangles, Washington (USGS)l and Interactive Geologic
Hazard Maps (WSDNR)2. Based on review of the geologic maps, the primary geologic unit in the vicinity
of the site is Pleistocene continental glacial drift (Qgd). This Glacial Drift comprises a range of materials,
including till, outwash clay, silt, sand, gravel, cobbles, and boulders, all of which were deposited by or
originated from continental glaciers. In the course of our explorations, we encountered sediments akin
to till and outwash deposits. Our interpretation of these sediments corresponds with the broader
regional geologic mapping.
1 Minard, J.P., 1983, Geologic map of the Edmonds East and part of the Edmonds West quadrangles, Washington, U.S.
Geological Survey, Miscellaneous Field Studies Map MF-1541, 1:24,000.
2 https://www.dnr.wa.gov/geologyportal
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3.3 SOIL CONDITIONS
The enclosed exploration test pit logs in Appendix A provide a detailed description of the encountered
soil strata. Our investigation revealed that the soils primarily comprise Glacial Drift deposits,
accompanied by a top layer of Topsoil/Fill, measuring up to 4.0 feet in thickness. Presented below is a
summarized portrayal of the soil compositions found within the test pits.
Topsoil — A surficial layer of topsoil was encountered at all of our test pits. The topsoil consisted
of loose sandy silt soil with organics and was generally about 6-inches thick. The topsoil was
characterized by its dark brown color and a dense mat of roots. This soil layer is not considered
suitable for support of foundations, slab -on -grade floors, or pavements. In addition, it is not
suitable for use as structural fill, nor should it be mixed with materials to be used as structural
fill.
Fill — Fill was encountered to a depth up to 4.0 feet below existing grade. The fill was likely placed
during construction of the existing residential dwelling. The fill consisted of silty sand with some
gravel, which was characterized by its medium dense condition and the presence of scattered
organics.
Glacial Drift Deposits — Glacial Drift deposits were encountered to a depth of up to 9 feet below
the existing grade. These deposits comprised a non -stratified mixture of light to grayish light
brown silt, sand, and gravel. Typically, the soil exhibited a medium -density profile, transitioning
to a denser composition at approximately 6.0 feet below the existing grade.
Our geotechnical laboratory tests indicated that the moisture contents of the Glacial Drift soils during
our exploration varied between 13% and 17%. Furthermore, the fines content, measured by the
percentage passing the U.S. No. 200 screen, ranged from 11% to 15%. The laboratory testing sheets in
Appendix B visually depict our test results.
3.4 GROUNDWATER CONDITIONS
Groundwater seepage was not encountered during our investigation on September 23, 2023. However,
it should be noted that perched groundwater can occur atop dense silty sand soils as downward
percolation of groundwater is inhibited by the less permeable soils. Groundwater levels may fluctuate
throughout the year in response to precipitation patterns, on- or off -site construction, irrigation
activities, and site utilization.
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3.5 SUBSURFACE CONTAMINATION
Throughout our exploration program, no visually discernible contaminated soil was identified within the
subject site.
4.0 ENVIRONMENTALLY CRITICAL AREAS CONSIDERATIONS
As part of our study, we conducted a comprehensive review of potential geologic hazards at the subject
site, as outlined in the City of Edmonds Community Development Code (ECDC) Chapter 23.80,
'Geologically Hazardous Areas', in alignment with the Critical Areas Determination (CRA2023-0089)
letter dated June 8, 2023.
4.1 EROSION HAZARDS
The definition of Erosion Hazard Areas is outlined in ECDC Chapter 23.80.020, 'Designation of specific
hazard areas,' and is provided below:
Erosion hazard areas are at least those areas identified by the U.S. Department of Agriculture's Natural
Resources Conservation Service as having a "moderate to severe," "severe,"or "very severe" rill and inter -
rill erosion hazard. Erosion hazard areas are also those areas impacted by shoreland and/or stream bank
erosion. Within the city of Edmonds erosion hazard areas include:
1. Those areas of the city of Edmonds containing soils that may experience severe to very severe erosion
hazard. This group of soils includes, but is not limited to, the following when they occur on slopes of 15
percent or greater:
a. Alderwood soils (15 to 25 percent slopes),
b. Alderwood/Everett series (25 to 70 percent slopes),
c. Everett series (15 to 25 percent slopes),
2. Coastal and stream erosion areas which are subject to the impacts from lateral erosion related to
moving water such as stream channel migration and shoreline retreat;
3. Any area with slopes of 15 percent or greater and impermeable soils interbedded with granular soils
and springs or ground water seepage; and
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4. Areas with significant visible evidence of ground water seepage, and which also include existing
landslide deposits regardless of slope.
Our assessment of the NRCS Soil Survey' indicates that the property is categorized as Alderwood gravelly
sandy loam with slopes ranging from 15 to 30 percent. The Alderwood series has a parent material
consisting of lodgement till, which aligns with the Glacial Drift soils encountered during our
investigations near the slope. Based on our analysis of the NRCS data, the property meets the criteria for
erosion hazard. While we understand that the project does not propose any construction activities on
or near the slopes, we have nonetheless provided erosion mitigation recommendations in the following
section.
It is our professional opinion that by adhering to the recommendations outlined in this report:
• The project will not increase surface water discharge or sedimentation to adjacent properties or
stormwater systems beyond predevelopment conditions.
• The project will not compromise slope stability on adjacent properties.
• The project will not adversely affect other critical areas.
To minimize sediment transport from the site during construction, the following recommendations
should be followed:
• Install silt fencing around the lower perimeter of all cleared areas, conducting periodic
inspections and maintenance as required to ensure proper functioning.
• Whenever possible, schedule earthwork -related construction during drier periods of the year and
promptly revegetate disturbed areas. Maintain temporary erosion control measures until
permanent erosion control measures are established.
• Mulch and hydroseed areas stripped of vegetation during construction as soon as possible,
especially during winter construction when hydroseeded areas should be covered with clear
plastic to facilitate grass growth.
• If excavated soils are stockpiled on -site for reuse, implement measures to minimize erosion
potential, including covering the pile with plastic sheeting, using low stockpiles in flat areas, and
employing straw bales or silt fences around pile perimeters.
• Construct interceptor swales with rock check dams to divert stormwater from construction areas
and route collected stormwater to an appropriate discharge location.
• Provide a rock construction entrance to reduce sediment transport off -site on truck tires.
• Direct all stormwater from impermeable surfaces, such as driveways and roofs, into approved
facilities rather than onto or above steeply sloping areas.
• Avoid sediment track -out onto City streets.
3 https:Hwebsoilsurvey.nres.usda.gov/app/WebSoiISurvey.aspx
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4.2 LANDSLIDE HAZARD AREAS
The ECDC defines landslide hazard areas as potentially subject to landslides based on a combination of
geologic, topographic, and hydrologic factors. They include areas susceptible because of any
combination of soil, slope (gradient), slope aspect, structure, hydrology, or other factors. Within the
City of Edmonds potential landslide hazard areas include:
1. Areas of ancient or historic failures in Edmonds which include all areas within the earth
subsidence and landslide hazard area as identified in the 1979 report of Robert Lowe Associates
and amended by the 1985 report of GeoEngineers, Inc., and further discussed in the 2007 report
by Landau Associates;
2. Coastal areas mapped as class u (unstable), uos (unstable old slides), and urs (unstable recent
slides) in the Department of Ecology Washington coastal atlas;
3. Areas designated as quaternary slumps, earthflows, mudflows, or landslides on maps
published by the United States Geological Survey or Washington State Department of Natural
Resources;
To assess the landslide hazard at the subject site, we conducted a thorough review, encompassing the
Geologic map of the Edmonds East and part of the Edmonds West quadrangles, Washington (Minard et
al, 1983), the State of Washington DNR Geologic Hazard Map, as well as historical slope stability
information stored within our library and files. Furthermore, a site reconnaissance was undertaken on
September 23, 2023, encompassing an evaluation of the site and its slopes. The objective of this
reconnaissance was to appraise the state of the site's slopes and detect signs of historical slope instability,
encompassing:
• Bowl -shaped topography;
• Irregular or hummocky topography;
• Tension cracks, scarps, or other indicators of ground movement;
• Leaning or pistol -butted trees;
• Distressed vegetation;
• Vegetation of markedly different ages or types;
• "Fresh" looking soil deposited at the base of steep slopes;
• Disturbed or destroyed anthropogenic features, such as fence lines that have been displaced;
• Hillside seeps or springs; and
• Ponding water/sag ponds.
Upon evaluating the conditions observed during our thorough reconnaissance, we did not discern any
indications of historical slope instability. Furthermore, our test pits did not yield soils consistent with
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landslide deposits. The site's underlying native soils comprise Glacial Drift deposits, characterized by
their relatively robust strength. Notably, no signs of planes of weakness or preferential failure surfaces
were encountered. Importantly, the site's proximity to watercourses or water bodies, which could
potentially lead to erosion or slope undercutting, was absent. Throughout the exploration on September
23, 2023, groundwater was not encountered.
After meticulous review of the observed site conditions, we hold the opinion that the proposed
construction will not amplify the geological hazard risk to neighboring properties beyond pre -
development status. Furthermore, it will not adversely affect other critical areas. Therefore, in our
opinion, the development can be securely integrated into the site and does not align with ECDC's
definition of a Landslide Hazard Area.
5.0 CONCLUSIONS AND RECOMMENDATIONS
The conclusions and recommendations contained in this report are based on our understanding of the
currently proposed utilization of the project site, as derived from layout drawings, written information,
and verbal information supplied to us. Consequently, if any changes are made in the currently proposed
project, we may need to modify our conclusions and recommendations contained herein to reflect those
changes.
5.1 SITE PREPARATION
Preparation of the project site will involve temporary drainage, excavations, erosion control, dewatering,
and subgrade compaction. The paragraphs below discuss our geotechnical comments and
recommendations concerning site preparation.
Temporary Drainage
We recommend intercepting and diverting any potential sources of surface or near surface water within
the construction zones before stripping begins. Because the selection of an appropriate drainage system
will depend on the water quantity, season, weather conditions, construction sequence, and contractor's
methods, final decisions regarding drainage systems are best made in the field at the time of
construction. Nonetheless, we anticipate that curbs, berms, or ditches placed around the work areas will
adequately intercept surface water runoff.
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Erosion Control Measures
Because stripped surfaces and soil stockpiles are typically a source of runoff sediments, they should be
given particular attention. If earthwork occurs during wet weather, we recommend all stripped surfaces
be covered with straw to reduce runoff erosion. Similarly, soil stockpiles and cut slopes should be
covered with plastic sheeting for erosion protection. We also recommend a staked silt fence be installed
around the area to be disturbed. The base of the silt fence should be buried so that sediment cannot
pass beneath it, and the silt fence should be inspected and maintained during the time that the site soils
are exposed, on a periodic basis, and after any major rainstorm event. It may be prudent to maintain a
berm and swale around the downslope side of stripped areas and stockpiles to capture runoff water,
thereby reducing the downslope sediment transport. In addition, the stripped areas should be
revegetated as soon as possible, also reducing the potential for erosion.
Clearing and Stripping
After surface and near -surface water sources have been controlled, the construction areas should be
cleared and stripped of all trees, bushes, sod, organic soils, and debris. It should be realized that if the
stripping operation proceeds during wet weather, a generally greater stripping depth might be necessary
to remove disturbed moisture -sensitive soils; therefore, stripping is best performed during a period of
dry weather.
Subgrade Compaction
Exposed subgrades for footings, floors, pavements, and other structures should be compacted to a firm,
unyielding state before concrete elements or fill soils are placed. Any localized zones of loose soils
observed within a subgrade should be compacted to a dense condition. In contrast, any organic, soft, or
pumping soils observed within a subgrade should be over -excavated and replaced with a suitable
structural fill material.
Reuse of On -site Soils
The Glacial Drift material underlying the fill appears suitable for reuse as structural fill at their present
moisture content. However, aeration or sprinkling might be needed to achieve an optimum moisture
content during especially wet or dry conditions, respectively.
5.2 EXCAVATION AND SLOPES
Our comments and recommendations concerning excavations are presented below.
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Soil Conditions
Based on our explorations, we anticipate that site excavations will encounter medium dense fill or Glacial
Drift material. In our opinion, these soils can be readily excavated with conventional earth -working
equipment.
Groundwater Conditions
Groundwater seepage was not observed during our site exploration program. However, a perched
groundwater seepage might occur from infiltration of surface water during rain events. Ideally, the
excavations would be performed during the summer or early fall, when groundwater levels will tend to
be at a yearly low.
Dewatering
We anticipate that the excavation can be adequately dewatered by means of a series of internal ditches,
sump holes, and pumps. In all cases, the specific design of a dewatering system should be completed by
the contractor using groundwater level data appropriate for the time of earthwork.
Temporary Slopes and Excavations
Configuration and maintenance of safe working conditions, including temporary excavation stability, is
the responsibility of the contractor. All applicable local, state, and federal safety codes should be
followed. Temporary excavation should either be shored or sloped in accordance with Safety Standards
for Construction Work, Part N, Washington Administrative Code (WAC) 296-155-650 through 66411. The
soil type classification and maximum inclination based on Part N of the Safety Standards for Construction
Work, WAC 296-155-66401 and 66403 is provided below.
Soil Unit WAC Soil Type Maximum Inclination
Glacial Drift Soils Type C 1 % H:1 V
Safety Considerations
The stability of temporary excavation slopes is a function of many factors, including soil type, soil density,
slope inclination, slope height, the presence of groundwater, and the duration of exposure. Generally,
the likelihood of slope failure increases as the cut is deepened and as the duration of exposure increases.
For this reason, we recommend the contractor maintain adequate slopes and/or setbacks. Temporary
slope safety should remain the responsibility of the contractor, who is continually present at the site and
is able to monitor the performance of the excavation and modify his activities to reflect varying
conditions. In all cases, cut -slope inclinations should conform to applicable governmental safety
guidelines.
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Slope Protection
Regardless of inclination, temporary slopes should be protected from surface -runoff erosion. Typically,
this can be accomplished by means of berms or swales located along the top of the slope, and possibly
by means of plastic tarpaulins placed over the slope.
5.3 SEISMIC DESIGN PARAMETERS
The 2015 International Building Code (IBC) seismic design section provides a basis for seismic design of
structures. Computation of forces used for seismic design for this code is based on seismological input
and site soil response factors. Ground motions considered for evaluation using these guidelines are
defined as motions with approximately 2 percent probability of exceedance in 50 years, or about a 2,500-
year return period.
Characterization of soil profile type is required in the IBC to determine the site class definition. Based on
the dense nature of Glacial Drift and soil classifications derived from the explorations completed at the
site, the site could be classified as Site Class D. The spectral response accelerations were obtained from
the USGS Earthquake Hazards Program for the project latitude and longitude. Table 2 below provides
seismic design parameters for the site that are in conformance with the 2015 IBC.
Table 2. Seismic Design Parameters
Site location
Latitude =
47.8326017
Longitude =
1 -122.357287
Recommended Site Class
D
Seismic Design Code
IBC 2015
Structural Analysis: Risk -targeted MCE (MCER)
Mapped Spectral Response Acceleration
Parameters
(Site Class B)
Short -Period, Ss =
1.287 g
1-second Period, S1=
0.505 g
Site Coefficients
Short -Period, Fa =
1.000
Long -Period, F =
1.5
Spectral Response Acceleration
Parameters Adjusted for Site Class
SMs = Fa x Ss =
1.287 g
SMi = Fv x S1=
0.757 g
Design Spectral Response Acceleration
Parameters
Sos = 2/3 x SMs =
0.858 g
SD1 = 2/3 x SMi =
0.505 g
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5.4 LIQUEFACTION POTENTIAL
Soil liquefaction results from loss of strength during cyclic loading, such as imposed by earthquakes. Soils
most susceptible to liquefaction are clean, loose, saturated, uniformly graded sand below the
groundwater table. Empirical evidence indicates that silts and low plasticity clays (fine-grained soils) are
also potentially liquefiable, though this phenomenon is commonly referred to as cyclic softening. When
seismic ground shaking occurs, the soil is subjected to cyclic shear stresses that can cause excess
hydrostatic pressures to develop. If excess hydrostatic pressures exceed the effective confining stress
from the overlying soil, the soil may undergo deformation. If the soil consolidates or vents to the surface
during and following liquefaction, ground settlement and surface deformation may occur.
The substrate of the subject site comprises medium dense to dense silty sand with gravel (Glacial Drift).
During the exploration on September 23, 2023, no groundwater was encountered. Given these
conditions and considering the project's scope of work, in our opinion, the liquefaction potential of the
site is relatively low, and there is no need for design considerations related to soil liquefaction for this
project.
5.5 BUILDING FOUNDATIONS
Based on the subsurface conditions encountered at the site and our understanding of the planned
development, it is our opinion that shallow conventional isolated or continuous footings may be
employed across the site, provided they are established on the undisturbed native soil or on suitably
compacted structural fill placed directly over these soils. The ensuing comments and recommendations
are offered to guide the footing design and construction process.
Footing Depths and Widths
For frost and erosion protection, exterior footings should be embedded at least 18 inches below adjacent
outside grade, whereas interior footings need extend only 12 inches below the surrounding slab surface
level. For the purpose of reducing post -construction settlements, we recommend that continuous (wall)
footings should have a minimum width of 18 inches, while isolated (column) footings should be at least
24 inches wide.
Bearing Pressures
We recommend that all footings bear on the undisturbed Glacial Drift Deposits or on properly compacted
structural fill placed directly over these soils. Footings that bear on properly prepared native or structural
fill subgrades can be designed for the following maximum allowable soil bearing pressures for static
loadings:
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Footing Subgrade Allowable Bearing
Capacity
Static
Compacted Structural Fill over 2,000 psf
Undisturbed Glacial Drift Deposits
Undisturbed Glacial Drift Deposits 2,500 psf
These static bearing pressures can be increased by one-third when used with alternative basic load
combinations that include wind or earthquake loads. This recommendation is in accordance with the
International Building Code (IBC) 2021, Section 1806.
Subgrade Verification
All footing subgrades should consist of firm, unyielding, non -organic, native soils or compacted structural
fill materials. Under no circumstances should footings be cast atop loose, soft, or frozen soil, slough,
debris, existing uncontrolled fill, or surfaces covered by standing water. We recommend that the
condition of all subgrades be verified by a MPE geotechnical engineer before any fill or concrete is placed.
Footing Settlements:
We estimate that the total post -construction settlement of properly sized footings bearing on properly
prepared subgrades will not exceed 1 inch. Differential settlements may approach one-half of the total
settlement over horizontal distances on the order of 50 feet.
5.6 SLAB -ON -GRADE FLOORS
In our opinion, if subgrades are prepared as described in the Site Preparation section of this report, a
soil -supported slab -on -grade floor may be used for the proposed residence. We offer the following
comments and recommendations concerning slab -on -grade floors.
Subgrade Conditions and Verification
All soil -supported slab -on -grade floors should bear on firm, unyielding native soils or on suitable
structural fill soils. We recommend that the condition of all subgrades and overlying layers be verified
by a MPE geotechnical engineer prior to any fill or concrete is placed.
MP ENGINEERING, PLLC MPGEOTECH.COM 15
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Flnnr Ci ihhaca
Structural fill subbases do not appear to be needed under soil -supported slab -on -grade floors at the site.
However, the final decision regarding the need for subbases should be based on actual subgrade
conditions observed at the time of construction.
Caoillary Break
To retard the upward wicking of groundwater beneath the floor slab, we recommend that a capillary
break be placed over the subgrade. Ideally, this capillary break would consist of a 4-inch-thick layer of
pea gravel or other clean, uniform, gravel, such as "Gravel Backfill for Drains" per 2023 WSDOT Standard
Specification 9-03.12(4).
Vapor Retarder
We recommend that a layer of plastic sheeting (such as Visqueen or Moistop) be placed directly between
the capillary break and the floor slab to prevent ground moisture vapors from migrating upward through
the slab. During subsequent casting of the concrete slab, the contractor should exercise care to avoid
puncturing this vapor barrier.
5.7 DRAINAGE SYSTEMS
In our opinion, the proposed structure should be provided with permanent drainage systems to minimize
the risk of future moisture problems. We offer the following recommendations and comments for
drainage design and construction purposes.
Grading and Capping
Final site grades should slope downward away from the structure so that runoff water will flow by gravity
to suitable collection points, rather than ponding near the structure. Ideally, the area surrounding the
structure would be capped with concrete, asphalt, or low -permeability (silty) soils to reduce surface -
water infiltration.
Perimeter Drains
We recommend that the structure be encircled with a perimeter drain system to collect seepage water.
This drain should consist of a 4-inch diameter PVC perforated pipe within an envelope of pea gravel or
washed rock, extending at least 6 inches on all sides of the pipe, and the gravel envelope should be
wrapped with filter fabric to reduce the migration of fines from the surrounding soils. The perimeter
drain should be located near the base of the footings.
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Runoff Water
Roof -runoff and surface -runoff water should not be allowed to flow into the perimeter foundation
drainage systems. Instead, these sources should flow into separate tightline pipes and be routed away
from the structure to a storm drain or other appropriate location.
5.8 SITE UTILITIES
The following sections provide geotechnical recommendations for design and construction of new site
utilities. Geotechnical recommendations include trench excavation and support, construction
dewatering, pipe foundation support, pipe bedding, and trench backfill and compaction criteria. Please
note, for any new utilities within public right-of-way, local standards will supersede the
recommendations below.
Trench Excavation and Support
We anticipate excavations for underground utilities will primarily be within medium dense to dense
fill/native soils. A heavy-duty, hydraulic excavator with sufficient reach should be able to excavate the
proposed trenches to the expected depths. Upon reaching the trench bottom, we suggest that a smooth -
bladed bucket be used to clean the bottom of loose and/or disturbed soil. The final trench bottom should
be firm and free of loose and disturbed soil.
Trench configurations and maintenance of safe working conditions, including temporary excavation
stability, should be the responsibility of the contractor. All applicable local, state, and federal safety
codes should be followed. Temporary excavations for utilities should meet the requirements detailed in
Section 5.2 of this report. If groundwater seepage is present, flatter slopes, temporary shoring, and/or
dewatering may be required. Appropriately sized trench boxes should provide adequate support for
shallow excavations, provided the trench is properly dewatered and settlement -sensitive structures and
utilities are not situated immediately adjacent to the excavation. Trench boxes should meet the
requirements in Safety Standards for Construction Work, Part N (WAC Chapter 296-155).
Construction Dewatering
We anticipate perched groundwater may be encountered within the trench zone, particularly during
winter and spring. If perched, water -bearing zones are encountered, construction dewatering can be
achieved following the procedures in Section 5.2 of this report.
Pipe Foundation Support
Based on the conditions observed in our explorations, dense soils are anticipated at the base of utility
trenches. The soil will provide adequate foundation support for utilities, provided the foundation soil
MP ENGINEERING, PLLC MPGEOTECH.COM 17
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remains in a relatively undisturbed condition. If the bottom of the trench becomes disturbed due to
excavation and/or foot traffic during the laying of the pipe, the disturbed material should be
overexcavated to expose undisturbed foundation soil. The overexcavation should be backfilled with
suitable foundation material to provide a firm trench bottom. Foundation material should be free of
roots, topsoil, lumps of silt and clay, and organic and inorganic debris.
Pipe Bedding
Pipe zone bedding material should consist of crushed, processed, or naturally occurring granular material,
free of organic matter and other deleterious material, and should meet the gradation requirements of
Gravel Backfill for Pipe Zone Bedding per Section 9-03.12(3) of the 2023 WSDOT Standard Specifications.
Trench Backfill and Compaction
Trench backfill material should meet the material and compaction requirements as described in Section
5.9 of this report.
5.9 STRUCTURAL FILL
The term "structural fill" refers to any materials placed under foundations, slab -on -grade floors,
sidewalks, pavements, and other structures. Our comments, conclusions, and recommendations
concerning structural fill are presented in the following paragraphs.
Materials
Typical structural fill materials include gravel, crushed rock, quarry spalls, CDF, LMC, well -graded
mixtures of sand and gravel (commonly called "gravel borrow" or "pit -run"), and miscellaneous mixtures
of silt, sand, and gravel. Soils used for structural fill should not contain any organic matter or debris, or
any individual particles greater than approximately 6 inches in diameter.
Fill Placement
Generally, quarry spalls, CDF, and LMC do not require special placement and compaction procedures. In
contrast, gravel, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifts
not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted with a
mechanical vibratory compactor.
Compaction Criteria
Using the Modified Proctor test (ASTM D1557) as a standard, we recommend structural fill be used for
various on -site applications and compacted to the following minimum densities:
MP ENGINEERING, PLLC MPGEOTECH.COM 18
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Minimum
Fill Application Compaction
Footing subgrade and bearing pad 95 percent
Footing and stemwall backfill 90 percent
Slab -on -grade floor subgrade 95 percent
Concrete sidewalk subgrade 90 percent
Utility trench backfill (below 4 feet) 90 percent
Utility trench backfill (above 4 feet) 95 percent
Utility trench backfill (under building 95 percent
footings or structures)
Subarade Verification and Compaction Testi
Regardless of material or location, all structural fill should be placed over firm, unyielding subgrades
prepared in accordance with the Site Preparation section of this report. The condition of all subgrades
should be verified by a WE representative before filling or construction begins. In addition, fill soil
compaction should be verified by means of in -place density tests performed during fill placement so
adequacy of the soil compaction efforts may be evaluated as earthwork progresses.
Soil Moisture Considerations
The suitability of soils used for structural fill depends primarily on their grain -size distribution and
moisture content when they are placed. As the "fines" content (the soil fraction passing the U.S. No. 200
Sieve) increases, soils become more sensitive to small changes in moisture content. Soils containing
more than about 5 percent fines (by weight) cannot be consistently compacted to a firm, unyielding
condition when the moisture content is more than 2 percentage points above or below optimum. For fill
placement during wet -weather site work, we recommend using "clean" fill, which refers to soils that
have a fines content of 5 percent or less (by weight) based on the soil fraction passing the U.S. No. 4
Sieve.
CDF Strength Considerations
Controlled Density Fill (CDF) is normally specified in terms of its compressive strength, which typically
ranges from 50 to 200 pounds per square inch (psi). CDF having a strength of 50 psi (7,200 psf) provides
adequate support for most structural applications and can be readily excavated with hand shovels. A
strength of 100 psi (14,400 psf) provides additional support for special applications but greatly increases
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the difficulty of hand -excavation. In general, CDF having a strength greater than about 100 psi requires
power equipment to excavate and should not be used where future hand -excavation might be needed.
6.0 ADDITIONAL SERVICES
MPE should be retained to review the final design plans and specifications so comments can be made
regarding interpretation and implementation of our geotechnical recommendations in the design and
specifications. MPE also should be retained to provide monitoring services during site preparations and
grading, and other earth -related construction phases of the project.
7.0 CLOSURE
This report has been prepared for the exclusive use of Mr. Caleb Macllvaine and their consultants for
specific application to this project, in accordance with generally accepted geotechnical engineering
practices. No warranties, either expressed or implied, are intended or made. Site safety, excavation
support, and dewatering requirements are the responsibility of others. In the event that changes in the
nature, design, or location of the project as outlined in this report are planned, the conclusions and
recommendations contained in this report shall not be considered valid unless MPE reviews the changes
and either verifies or modifies the conclusions of this report in writing.
The recommendations presented herein have been developed on the basis of the subsurface conditions
encountered during the field investigation and our understanding of the proposed construction. Should
changes in the project criteria occur or additional loading information becomes available, a review must
be made by MPE to determine if modifications to our recommendations will be required.
The analysis and recommendations presented in this report are based upon the data obtained from the
test pits performed at the indicated locations and from other information discussed in this report. This
report does not reflect variations that may occur between test pits, across the site, or due to the
modifying effects of construction or weather. The nature and extent of such variations may not become
evident until during or after construction. If variations appear, we should be immediately notified so
that further evaluation and supplemental recommendations can be provided. We are available to
provide geotechnical engineering throughout the design process, and construction and quality assurance
monitoring during construction.
It is the client's responsibility to see that all parties to this project, including the designer, contractor,
subcontractors, etc., are made aware of this report in its entirety. The use of information contained in
MP ENGINEERING, PLLC MPGEOTECH.COM 20
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MP ENGINEERING
this report for bidding purposes should be done at the contractor's option and risk. Any party other than
the client who wishes to use this report shall notify MPE of such intended use and for permission to copy
this report. Based on the intended use of the report, MPE may require that additional work be performed
and that an updated report be reissued. Noncompliance with any of these requirements will release MPE
from any liability resulting from the use this report.
Sincerely,
MP Engineering, PLLC
NE
�-� V4A
Date: 10-06-2023
Minjae Park, P.E.
Principal Geotechnical Engineer
Date: 10-06-2023
Jintae Lee, Ph.D., P.E.
Geotechnical Specialist
MP ENGINEERING, PLLC MPGEOTECH.COM 21
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PROJECT NO. I FIGURE NO.
23-0104
W
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Approximate Proposed TP-01
Test Pit Location
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APPENDIX A
FIELD EXPLORATION PROCEDURES AND LOGS
APPENDIX A
FIELD EXPLORATION PROCEDURES AND LOGS
PROJECT NO. 23-0104
The following paragraphs describe the procedures used for field explorations and field tests that
MPE conducted for this project. Descriptive logs of our explorations are enclosed in this appendix.
TEST PIT PROCEDURES
Our exploratory test pits were excavated with a post hole digger and a hand auger operated by
MPE. A geotechnical engineer from our firm continuously observed the test pit excavations,
logged the subsurface conditions, and obtained representative soil samples. All samples were
stored in watertight containers and later transported to a laboratory for further visual
examination and testing. After we logged each test pit, the operator backfilled it in lifts and
compacted each lift to a firm or firm and unyielding condition. The enclosed Test Pit Logs indicate
the vertical sequence of soils and materials encountered in each test pit, based primarily on our
field classifications and supported by subsequent laboratory examination and testing. Where a
soil contact was observed to be gradational or undulating, our logs indicate the average contact
depth. We estimated the relative density and consistency of the in situ soils by means of the
excavation characteristics and the stability of the test pit sidewalls. Our logs also indicate the
approximate depths of any sidewall caving or groundwater seepage observed in the test pits, as
well as all sample numbers and sampling locations.
TEST PIT LOG
Test Pit Designation TP-01
PROJECT 9222 183RD PL SW
JO&1.
MP ENGINEERING
MP ENGINEERING
2. LOCATION Edmonds, Washington
3. EXCAVATION CONTRACTOR MP ENGINEERING
4. APPROXIMATE GROUND SURFACE ELEVATION 21 O'
5. OPERATOR EQUIPMENT Post Hole Digger
6. LOCATION COORDINATES N 47.83268 W 122.357383
7. DATE STARTED DATE COMPLETED
8. COORDINATE SYSTEM HORIZONTAL VERTICAL
9/23/23 9/23/23
State Plane NAD83 NAVD88
9. TOTAL DEPTH OF TEST PIT 9'
10. APPROXIMATE GROUND WATER ELEVATION N/A
11. LOGGER JINTAE LEE, Engineer
12. TIME OF READING ATD
U
ELEV
(FT)
DEPTH
(ft)
' o
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SOIL DESCRIPTION
LAB
TESTING
SAMPLE
NO.
REMARKS
0
0
`.
Topsoil
209.5
Medium dense, moist, brown, silty SAND with some
gravel, and scattered organics (FILL)
1
208.0
2
Medium dense, moist, light brown, silty SAND with
some gravel (SM)
3
4
S-1
205.5
Medium dense to dense, moist to wet, grayish light
brown, gravelly SAND with some silt (SP-SM)
5
6
:.
_ _ _
Grades to Den.....................
e
7
8
S-2
WC = 17%
Fines = 11 %
201.0
9
BOTTOM OF TEST PIT AT 9.0 ft
SHEET 1 of 1
TEST PIT LOG
Test Pit Designation TP-02
PROJECT 9222 183RD PL SW
JO&1.
MP ENGINEERING
MP ENGINEERING
2. LOCATION Edmonds, Washington
3. EXCAVATION CONTRACTOR MP ENGINEERING
4. APPROXIMATE GROUND SURFACE ELEVATION 218'
5. OPERATOR EQUIPMENT Post Hole Digger
6. LOCATION COORDINATES N 47.83238 W 122.357214
7. DATE STARTED DATE COMPLETED
8. COORDINATE SYSTEM HORIZONTAL VERTICAL
9/23/23 9/23/23
State Plane NAD83 NAVD88
9. TOTAL DEPTH OF TEST PIT 9'
10. APPROXIMATE GROUND WATER ELEVATION N/A
11. LOGGER JINTAE LEE, Engineer
12. TIME OF READING ATD
U
ELEV
(FT)
DEPTH
(ft)
' o
K �
SOIL DESCRIPTION
LAB
TESTING
SAMPLE
NO.
REMARKS
0
0
`. Topsoil
217.5
------------------------
Medium dense, moist, brown, silty SAND with some
gravel, and scattered organics (FILL)
1
216.5
Medium dense, moist, light brown, silty SAND with
some gravel (SM)
2
3
S-1
214.0
4
Medium dense to dense, moist to wet, grayish light
brown, gravelly silty SAND (SM)
5
.................
Grades to Dense
6
7
S-2
WC = 15%
Fines = 15%
8
209.0
9
BOTTOM OF TEST PIT AT 9.0 ft
SHEET 1 of 1
TEST PIT LOG
Test Pit Designation TP-03
PROJECT 9222 183RD PL SW
JO&1.
MP ENGINEERING
MP ENGINEERING
2. LOCATION Edmonds, Washington
3. EXCAVATION CONTRACTOR MP ENGINEERING
4. APPROXIMATE GROUND SURFACE ELEVATION 213'
5. OPERATOR EQUIPMENT Post Hole Digger
6. LOCATION COORDINATES N 47.832548 W 122.357185
7. DATE STARTED DATE COMPLETED
8. COORDINATE SYSTEM HORIZONTAL VERTICAL
9/23/23 9/23/23
State Plane NAD83 NAVD88
9. TOTAL DEPTH OF TEST PIT 91
10. APPROXIMATE GROUND WATER ELEVATION N/A
11. LOGGER JINTAE LEE, Engineer
12. TIME OF READING ATD
U
ELEV
(FT)
DEPTH
(ft)
' o
K �
SOIL DESCRIPTION
LAB
TESTING
SAMPLE
NO.
REMARKS
0
0
`.
Topsoil
212.5
Medium dense, moist, brown, silty SAND with some
------------------------
gravel, and scattered organics (FILL)
1
2
3
209.0
4
---------------------
Medium dense to dense, moist to wet, grayish light
brown, gravelly silty SAND (SM)
5
6
.•
_ _ _
Grades to Den......................
e
7
WC = 13%
S-1
8
Fines = 14%
204.0
1 9
BOTTOM OF TEST PIT AT 9.0 ft
SHEET 1 of 1
APPENDIX B
LABORATORY TESTING PROCEDURES AND RESULTS
APPENDIX B
LABORATORY TESTING PROCEDURES AND RESULTS
PROJECT NO. 23-0104
The following paragraphs describe procedures associated with the laboratory tests conducted
for this project. Graphical results of certain laboratory tests are enclosed in this appendix.
VISUAL CLASSIFICATION PROCEDURES
Visual soil classifications were conducted on all samples in the field and on selected samples in
the laboratory. All soils were classified in general accordance with the Unified Soil Classification
System, which includes color, relative moisture content, primary soil type (based on grain size),
and any accessory soil types. The resulting soil classifications are presented on the exploration
logs contained in Appendix A.
MOISTURE CONTENT DETERMINATION PROCEDURES
Moisture content determinations were performed on representative samples to aid in
identification and correlation of soil types. All determinations were made in general accordance
with ASTM D-2216. The results of these tests are shown on the exploration logs in Appendix A.
GRAIN -SIZE ANALYSIS PROCEDURES
A grain -size analysis indicates the range of soil particle diameters included in a particular sample.
Grain -size analyses were performed on representative samples in general accordance with ASTM
D-422. The results of these tests are presented on the enclosed grain -size distribution graphs and
were used in soil classifications shown on the exploration logs in Appendix A.
100
90
80
70
x
c7
w 60
co
m
w 50
Z
LL
H
Z
u 40
W
a
30
20
10
0
MP Engineering Sieve Analysis
r-1
r-1
mm
mm
Em
100.00
+3„
Sieve
Size
Percent
Finer
1.25"
100.0
ill
99.6
1 /2"
97.6
1 /4"
94.2
#4
88.0
#10
75.5
#40
69.9
#100
60.4
#140
51.0
#200
11.4
JOCS161h
MP ENGINEERING
10.00 1.00 0.10 0.01
GRAIN SIZE IN MILLIMETERS
% GRAVEL % SAND % FINES
coarse medium fine (Silt or Clay)
12.0 12.51 5.6 58.5 11.4
Sample Name: TP-01 / S-2
Sample Description: Poorly graded SAND with silt
Depth: 8.0' - 8.5'
Test Date: September 25, 2023
USCS (D-2487): SP-SM
Natural Moisture Content: 16.6% ASTM D-2216
D60: 0.4 mm
D30: 0.09 mm
1310:
MACLLVAINE PROPERTY
9222 183rd PI SW, Edmonds, WA 98020
PROJECT #23-0104
100
90
80
70
x
c7
W 60
Y
m
w 50
Z
LL
H
Z
u 40
W
a
Sieve
Size
Percent
Finer
1.25"
100.0
1"
99.1
1 /2"
93.2
1 /4"
89.3
#4
83.1
#10
67.1
#40
56.6
#100
43.4
#140
34.4
#200
15.1
jac**41616
MP ENGINEERING
MP Engineering Sieve Analysis
10.00 1.00
GRAIN SIZE IN MILLIMETERS
% GRAVEL % SAND
coarse medium I fine
16.9 16.01 10.5 1 41.,
0.10
% FINES
(Silt or Clay)
15.1
Sample Name: TP-02 / S-2
Sample Description: Silty SAND with gravel
Depth: 7.0' - 7.5'
Test Date: September 25, 2023
USCS (D-2487): SM
Natural Moisture Content: 14.6% ASTM D-2216
D60: 0.71 mm
D30: 0.09 mm
1310:
MACLLVAINE PROPERTY
9222 183rd PI SW, Edmonds, WA 98020
PROJECT #23-0104
0.01
100
90
80
70
x
c7
W 60
Y
m
w 50
Z
LL
H
Z
u 40
W
a
Sieve
Size
Percent
Finer
1.25"
100.0
ill
99.3
1 /2"
96.0
1 /4"
90.7
#4
84.0
#10
72.3
#40
62.5
#100
48.8
#140
34.6
#200
14.2
jac**41616
MP ENGINEERING
MP Engineering Sieve Analysis
10.00 1.00 0.10 0.01
GRAIN SIZE IN MILLIMETERS
% GRAVEL % SAND % FINES
coarse medium I fine (Silt or Clay)
16.0 11.71 9.8 1 48.2 14.2
Sample Name: TP-03 / S-1
Sample Description: Silty SAND with gravel
Depth: 7.5' - 8.0'
Test Date: September 25, 2023
USCS (D-2487): SM
Natural Moisture Content: 13.3% ASTM D-2216
D60: 0.33 mm
D30: 0.09 mm
1310:
MACLLVAINE PROPERTY
9222 183rd PI SW, Edmonds, WA 98020
PROJECT #23-0104