REVIEWED BLD2023-0174+Geotechnical_Report+4.19.2023_10.13.38_AM+3491852BLD2023-0174
COBALT
GE0SCIENCES
RECEIVED
Apr 24 2023
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, Washington 98028
..............................................
REVIEWED
August 18, 2022 BY
CITY OF EDMONDS
Eric Ryner BUILDING DEPARTMENT
EricPrynerhomes.com................................................
RE: Geotechnical Evaluation
Proposed Residence
1050 Walnut Street
Edmonds, Washington
In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to
discuss the results of our geotechnical evaluation at the referenced site. The purpose of our
evaluation was to provide recommendations for foundation design, grading, and earthwork.
Site Description
The site is located at 1050 Walnut Street in Edmonds, Washington. The site consists of one
rectangular shaped parcel (No. 00434203501500) with a total area of o.16 acres.
The property is developed with a single-family residence and driveway. The remainder of the site
is vegetated with grasses, bushes and variable diameter trees. The site is nearly level to slightly
sloping downward to the north with minimal relief. There is a short block wall along the
driveway.
The site is bordered to the east, west, and south by residences, and to the north by Walnut Street.
The proposed development includes a new residence in the central portion of the site.
Stormwater will include infiltration or other systems depending on feasibility. Site grading may
include cuts and fills of 3 feet or less for foundation placement and structural loads are expected
to be light.
We should be provided with the final plans to verify that our recommendations remain valid and
do not require updating.
Area Geology
The Geologic Map of Edmonds East and West Quadrangles, indicates that the site is underlain by
Vashon Advance Outwash.
Vashon Advance Outwash includes fine to medium sand with local interbeds of silt and clay.
These deposits are typically permeable and become denser with depth.
Soil & Groundwater Conditions
As part of our evaluation, we excavated one test pit where accessible.
The explorations encountered approximately 6 inches of grass and topsoil underlain by
approximately 3.25 feet of loose to medium dense, silty -fine to medium grained sand trace gravel
(Weathered Advance Outwash). These materials were underlain by medium dense to dense, fine
to medium grained sand trace silt trace gravel (Advance Outwash), which continued to the
termination depths of the exploration.
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Geotechnical Evaluation
Groundwater was not encountered in the exploration. We do not anticipate groundwater to be
present at shallow depths in this area.
Water table elevations often fluctuate over time. The groundwater level will depend on a variety
of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and
soil permeability. Water levels at the time of the field investigation may be different from those
encountered during the construction phase of the project.
Erosion Hazard
The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that
the site is underlain by Everett very gravelly sandy loam (o to 8 percent slopes). These soils
would have a slight to moderate erosion potential in a disturbed state depending on the slope
magnitude.
It is our opinion that soil erosion potential at this project site can be reduced through landscaping
and surface water runoff control. Typically, erosion of exposed soils will be most noticeable
during periods of rainfall and may be controlled by the use of normal temporary erosion control
measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The
typical wet weather season, with regard to site grading, is from October 31st to April ist. Erosion
control measures should be in place before the onset of wet weather.
Seismic Hazard
The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the
International Building Code (IBC). A Site Class D applies to an overall profile consisting of
medium dense to very dense soils within the upper too feet.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to
obtain values for Ss, Sl, FQ, and F,,. The USGS website includes the most updated published data
on seismic conditions. The following tables provide seismic parameters from the USGS web site
with referenced parameters from 7-16.
Seismic Design Parameters (ASCE 7-16)
Site
Spectral
Spectral
Site
Design Spectral
Design
Class
Acceleration
Acceleration
Coefficients
Response Parameters
PGA
at 0.2 sec. (g)
at l.o sec. (g)
Fa
Fv
SDs
SD1
D
1.284
0.452
1.0
Null
0.856
Null
0.546
Additional seismic considerations include liquefaction potential and amplification of ground
motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a
high groundwater table. The site has a low likelihood of liquefaction. For items listed as "Null"
see Section 11.4.8 of the ASCE.
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August 18, 2022
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Geotechnical Evaluation
Conclusions and Recommendations
General
The site is underlain by weathered and unweathered outwash which becomes denser with depth.
The proposed residential structure may be supported on a shallow foundation system bearing on
medium dense or firmer native soils or on structural fill placed on the native soils. Local
overexcavation or recompaction of loose weathered native soils may be necessary depending on
the proposed elevations and locations of the new footings.
Infiltration is generally feasible in the coarser outwash deposits at depth. We should be provided
with the civil plans to verify suitability. Local overexcavation of any pieces or layers of silty -sand
or cemented soils will need to be removed. We can provide additional recommendations once a
civil plan has been prepared.
Site Preparation
Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich
soil and fill. Based on observations from the site investigation program, it is anticipated that the
stripping depth will be 6 to 18 inches. Deeper excavations will be necessary below large trees and
in any areas underlain by undocumented fill.
The native soils consist of silty -sand with gravel and poorly graded sand with silt. Most of the
native soils may be used as structural fill provided they achieve compaction requirements and are
within 3 percent of the optimum moisture. Some of these soils may only be suitable for use as fill
during the summer months, as they will be above the optimum moisture levels in their current
state. These soils are variably moisture sensitive and may degrade during periods of wet weather
and under equipment traffic.
Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of
3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve).
Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted
to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the
ASTM D 1557 test method.
Temporary Excavations
Based on our understanding of the project, we anticipate that the grading could include local cuts
on the order of approximately 3 feet or less for foundation and most of the utility placement. Any
deeper temporary excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in
loose native soils and fill, 1H:1V in medium dense native soils and 3/4H:1V in dense to very dense
native soils. If an excavation is subject to heavy vibration or surcharge loads, we recommend that
the excavations be sloped no steeper than 2H:1V, where room permits.
Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part
N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a
qualified person during construction activities and the inspections should be documented in daily
reports. The contractor is responsible for maintaining the stability of the temporary cut slopes
and reducing slope erosion during construction.
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Geotechnical Evaluation
Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather,
and the slopes should be closely monitored until the permanent retaining systems or slope
configurations are complete. Materials should not be stored or equipment operated within 10 feet
of the top of any temporary cut slope.
Soil conditions may not be completely known from the geotechnical investigation. In the case of
temporary cuts, the existing soil conditions may not be completely revealed until the excavation
work exposes the soil. Typically, as excavation work progresses the maximum inclination of
temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental
recommendations can be made. Soil and groundwater conditions can be highly variable.
Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that
the project can proceed and required deadlines can be met.
If any variations or undesirable conditions are encountered during construction, we should be
notified so that supplemental recommendations can be made. If room constraints or
groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed
by the WAC, temporary shoring systems may be required. The contractor should be responsible
for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences
and the project structural engineer review temporary shoring designs prior to installation, to
verify the suitability of the proposed systems.
Foundation Design
The proposed structure may be supported on a shallow spread footing foundation system bearing
on undisturbed dense or firmer native soils or on properly compacted structural fill placed on the
suitable native soils. Any undocumented fill and/or loose native soils should be removed and
replaced with structural fill below foundation elements. Structural fill below footings should
consist of clean angular rock 5/8 to 4 inches in size. We should verify soil conditions during
foundation excavation work.
For shallow foundation support, we recommend widths of at least 16 and 24 inches, respectively,
for continuous wall and isolated column footings supporting the proposed structure. Provided
that the footings are supported as recommended above, a net allowable bearing pressure of 2,500
pounds per square foot (psf) may be used for design.
A 1/3 increase in the above value may be used for short duration loads, such as those imposed by
wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted
to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing
excavations should be inspected to verify that the foundations will bear on suitable material.
Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or
adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12
inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower.
If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch.
Differential settlement, along a 25-foot exterior wall footing, or between adjoining column
footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most
settlement is expected to occur during construction, as the loads are applied. However, additional
post -construction settlement may occur if the foundation soils are flooded or saturated. All
footing excavations should be observed by a qualified geotechnical consultant.
Resistance to lateral footing displacement can be determined using an allowable friction factor of
0.40 acting between the base of foundations and the supporting subgrades. Lateral resistance for
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Geotechnical Evaluation
footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds
per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12
inches below grade in exterior areas). The frictional and passive resistance of the soil may be
combined without reduction in determining the total lateral resistance.
Care should be taken to prevent wetting or drying of the bearing materials during construction.
Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the
footing excavations, should be removed prior to placing concrete. The potential for wetting or
drying of the bearing materials can be reduced by pouring concrete as soon as possible after
completing the footing excavation and evaluating the bearing surface by the geotechnical engineer
or his representative.
Concrete Retaining Walls
The following table, titled Wall Design Criteria, presents the recommended soil related design
parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall
system is used. This has been included for new cast in place walls, if any are proposed.
Wall Design Criteria
"At -rest" Conditions (Lateral Earth Pressure — EFD+)
55 pcf (Equivalent Fluid Density)
"Active" Conditions (Lateral Earth Pressure — EFD+)
35 pcf (Equivalent Fluid Density)
Seismic Increase for "At -rest" Conditions
(Lateral Earth Pressure)
21H* (Uniform Distribution) 1 in 2,500 year
event
Seismic Increase for "At -rest" Conditions
(Lateral Earth Pressure)
14H* (Uniform Distribution)1 in 500 year event
Seismic Increase for "Active" Conditions
(Lateral Earth Pressure)
7H* (Uniform Distribution)
Passive Earth Pressure on Low Side of Wall
(Allowable, includes F.S. = 1.5)
Neglect upper 2 feet, then 275 pcf EFD+
Soil -Footing Coefficient of Sliding Friction (Allowable;
includes F.S. = 1.5)
0.40
'H is the height of the wall; Increase based on one in 500 year seismic event (io percent probability of being exceeded in
50 years),
+EFD — Equivalent Fluid Density
The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by
water accumulation behind the retaining walls. Uniform horizontal lateral active and at -rest
pressures on the retaining walls from vertical surcharges behind the wall may be calculated using
active and at -rest lateral earth pressure coefficients of 0.3 and 0.5, respectively. A soil unit weight
Of 125 pcf may be used to calculate vertical earth surcharges.
To reduce the potential for the buildup of water pressure against the walls, continuous footing
drains (with cleanouts) should be provided at the bases of the walls. The footing drains should
consist of a minimum 4-inch diameter perforated pipe, sloped to drain, with perforations placed
down and enveloped by a minimum 6 inches of pea gravel in all directions.
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Geotechnical Evaluation
The backfill adjacent to and extending a lateral distance behind the walls at least 2 feet should
consist of free -draining granular material. All free draining backfill should contain less than 3
percent fines (passing the U.S. Standard No. 200 Sieve) based upon the fraction passing the U.S.
Standard No. 4 Sieve with at least 30 percent of the material being retained on the U.S. Standard
No. 4 Sieve. The primary purpose of the free -draining material is the reduction of hydrostatic
pressure. Some potential for the moisture to contact the back face of the wall may exist, even with
treatment, which may require that more extensive waterproofing be specified for walls, which
require interior moisture sensitive finishes.
We recommend that the backfill be compacted to at least 90 percent of the maximum dry density
based on ASTM Test Method D1557. In place density tests should be performed to verify
adequate compaction. Soil compactors place transient surcharges on the backfill. Consequently,
only light hand operated equipment is recommended within 3 feet of walls so that excessive stress
is not imposed on the walls.
Stormwater Management Feasibility
The site is underlain by weathered and unweathered outwash. We performed a small scale pilot
infiltration test (PIT) in TP-1. The test was performed in general accordance with the Washington
State Department of Ecology stormwater manual.
The area was excavated to a testing depth of approximately 4.0 feet below the ground surface. The
design infiltration rate was determined by applying correction factors to the measured infiltration
rate as prescribed in Volume III, Section 3.3.6 of the DOE. The measured rate must be reduced
through appropriate correction factors for site variability (CFv), uncertainty of test method (CFT),
and degree of influent control (CFM) to prevent siltation and bio-buildup.
It should be noted that construction traffic or other disturbance to the target infiltration area
could compact the soil, which may decrease the effective infiltration rates. The correction factors
and resulting design infiltration rate are also shown in the table below.
Test
Test
Measured
Correction Factors
Design
Number
Depth (ft)
Infiltration
Infiltration
Rate (in/hr)
Rate
CFv
CFT
CFM
(in/hr)
TP-1
4.0
4.2
0.6
0.5
0.9
1.134
Infiltration appears to be feasible in the underlying outwash with less than 7 percent fines. We
recommend removal of any dense soils or silty -sand layers/pieces during system placement if
encountered. We should be on site during construction to verify the soil conditions.
We can provide additional recommendations upon request and once civil plans have been
prepared.
We should be provided with final plans for review to determine if the intent of our
recommendations has been incorporated or if additional modifications are needed.
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Geotechnical Evaluation
Slab -on -Grade
We recommend that the upper 12 inches of the native soils within slab areas be re -compacted to
at least 95 percent of the modified proctor (ASTM D1557 Test Method).
Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor
barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture
typically requires the usage of a vapor barrier. A materials or structural engineer should be
consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs
typically do not utilize vapor barriers.
The American Concrete Institutes ACI 36oR-o6 Design of Slabs on Grade and ACI 302.1R-04
Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier
selection and floor slab detailing.
Slabs on grade may be designed using a coefficient of subgrade reaction of 210 pounds per cubic
inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and
compacted as outlined above. A 4- to 6-inch-thick capillary break layer should be placed over the
prepared subgrade. This material should consist of pea gravel or 5/8 inch clean angular rock.
A perimeter drainage system is recommended unless interior slab areas are elevated a minimum
Of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should
consist of a 4-inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain
rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into
the drainage system. The perimeter drainage system should discharge by gravity flow to a
suitable stormwater system.
Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate
surface water flow away from the building and preferably with a relatively impermeable surface
cover immediately adjacent to the building.
Erosion and Sediment Control
Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to
wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment
control measures should be implemented, and these measures should be in general accordance
with local regulations. At a minimum, the following basic recommendations should be
incorporated into the design of the erosion and sediment control features for the site:
• Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance
of the site soils, to take place during the dry season (generally May through September).
However, provided precautions are taken using Best Management Practices (BMP's), grading
activities can be completed during the wet season (generally October through April).
• All site work should be completed and stabilized as quickly as possible.
• Additional perimeter erosion and sediment control features may be required to reduce the
possibility of sediment entering the surface water. This may include additional silt fences, silt
fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration
systems.
• Any runoff generated by dewatering discharge should be treated through construction of a
sediment trap if there is sufficient space. If space is limited other filtration methods will need
to be incorporated.
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Geotechnical Evaluation
Utilities
Utility trenches should be excavated according to accepted engineering practices following OSHA
(Occupational Safety and Health Administration) standards, by a contractor experienced in such
work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent
to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be
avoided. Depending upon the location and depth of some utility trenches, groundwater flow into
open excavations could be experienced, especially during or shortly following periods of
precipitation.
In general, sandy soils were encountered at shallow depths in the explorations at this site. These
soils have low cohesion and density and will have a tendency to cave or slough in excavations.
Shoring or sloping back trench sidewalls is required within these soils in excavations greater than
4 feet deep.
All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility
trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at
least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5
feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent
of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench
backfill in pavement areas should be compacted to at least 90 percent of the maximum dry
density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe
manufacturer's recommendations.
The contractor is responsible for removing all water -sensitive soils from the trenches regardless of
the backfill location and compaction requirements. Depending on the depth and location of the
proposed utilities, we anticipate the need to re -compact existing fill soils below the utility
structures and pipes. The contractor should use appropriate equipment and methods to avoid
damage to the utilities and/or structures during fill placement and compaction procedures.
CONSTRUCTION FIELD REVIEWS
Cobalt Geosciences should be retained to provide part time field review during construction in
order to verify that the soil conditions encountered are consistent with our design assumptions
and that the intent of our recommendations is being met. This will require field and engineering
review to:
■ Monitor and test structural fill placement and soil compaction
■ Observe bearing capacity at foundation locations
■ Observe slab -on -grade preparation
■ Verify infiltration system placement
■ Monitor foundation drainage placement
■ Observe excavation stability
Geotechnical design services should also be anticipated during the subsequent final design phase
to support the structural design and address specific issues arising during this phase. Field and
engineering review services will also be required during the construction phase in order to
provide a Final Letter for the project.
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Geotechnical Evaluation
CLOSURE
This report was prepared for the exclusive use of Eric Rymer and his appointed consultants. Any
use of this report or the material contained herein by third parties, or for other than the intended
purpose, should first be approved in writing by Cobalt Geosciences, LLC.
The recommendations contained in this report are based on assumed continuity of soils with
those of our test holes and assumed structural loads. Cobalt Geosciences should be provided with
final architectural and civil drawings when they become available in order that we may review our
design recommendations and advise of any revisions, if necessary.
Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is
the responsibility of Eric Rymer who is identified as "the Client" within the Statement of General
Conditions, and its agents to review the conditions and to notify Cobalt Geosciences should any of
these not be satisfied.
Sincerely,
Cobalt Geosciences, LLC
P�-NONrtiq
Q �OF WASy� B
489 6
CIST ER \�
8/18/2021
Phil Haberman, PE, LG, LEG
Principal
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August 18, 2022
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Geotechnical Evaluation
Statement of General Conditions
USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its
agent and may not be used by any third party without the express written consent of Cobalt
Geosciences and the Client. Any use which a third parry makes of this report is the responsibility
of such third parry.
BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this
report are in accordance with Cobalt Geosciences present understanding of the site specific
project as described by the Client. The applicability of these is restricted to the site conditions
encountered at the time of the investigation or study. If the proposed site specific project differs
or is modified from what is described in this report or if the site conditions are altered, this report
is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the
report to reflect the differing or modified project specifics and/or the altered site conditions.
STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in
accordance with the normally accepted standard of care in the state of execution for the specific
professional service provided to the Client. No other warranty is made.
INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and
statements regarding their condition, made in this report are based on site conditions
encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or
sampling locations. Classifications and statements of condition have been made in accordance
with normally accepted practices which are judgmental in nature; no specific description should
be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in
situ conditions can only be made to some limited extent beyond the sampling or test points. The
extent depends on variability of the soil, rock and groundwater conditions as influenced by
geological processes, construction activity, and site use.
VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be
encountered that are different from those described in this report or encountered at the test
locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected
conditions are substantial and if reassessments of the report conclusions or recommendations are
required. Cobalt Geosciences will not be responsible to any parry for damages incurred as a result
of failing to notify Cobalt Geosciences that differing site or sub -surface conditions are present
upon becoming aware of such conditions.
PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and
specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next
project stage (property acquisition, tender, construction, etc), to confirm that this report
completely addresses the elaborated project specifics and that the contents of this report have
been properly interpreted. Specialty quality assurance services (field observations and testing)
during construction are a necessary part of the evaluation of sub -subsurface conditions and site
preparation works. Site work relating to the recommendations included in this report should only
be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be
responsible for site work carried out without being present.
www.cobaltgeo.com (2o6) 331-1097
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Slab on Grade
Basement or Shallow Foundation Wall
12" Free Draining Backfill and/or Drainage Mat
Attached to Wall
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3//4" Washed Rock or
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Not to Scale
Cobalt Geosciences, LLC
PO Box 1792
Typical Foundation Drain Detail Attachment North Bend, WA 98045
• _ (2o6) 331-1097
GEOSCIENCES www.cobaltgeo.com
Philpcobaltgeo.com
Unified Soil Classification System (USCS)
MAJOR DIVISIONS
SYMBOL
TYPICAL DESCRIPTION
Clean Gravels
Gw
Well -graded gravels, gravels, gravel -sand mixtures, little or no fines
Gravels
(more than 50%
(less than 5%
fines)
GP
Poorly graded gravels, gravel -sand mixtures, little or no fines
COARSE
GRAINED
SOILS
of coarse fraction
retained on No. 4
sieve)
Gravels with
Fines
(more than 12%
fines)
GM
Silty gravels, gravel -sand -silt mixtures
GC
Clayey gravels, gravel -sand -clay mixtures
(more than 50%
retained on
Clean Sands
:•: sw
Well -graded sands, gravelly sands, little or no fines
No. 200 sieve)
Sands
(50% or more
of coarse fraction
(less than 5%
fines)
sP
Poorly graded sand, gravelly sands, little or no fines
passes the No. 4
sieve)
Sands with
Fines
sM
Silty sands, sand -silt mixtures
(more than 12%
fines)
sc
Clayey sands, sand -clay mixtures
ML
Inorganic silts of low to medium plasticity, sandy silts, gravelly silts,
FINE GRAINED
(50% or more
Silts and Clays
(liquid limit less
than 50)
Inorganic
cL
or clayey silts with slight plasticity
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays
silty clays, lean clays
Organic rganic
oL
Organic silts and organic silty clays of low plasticity
passes the
MH
Inorganic silts, micaceous or diatomaceous fine sands or silty soils,
No. 200 sieve)
Silts and Clays
(liquid limit 50 or
more)
Inorganic
elastic silt
CH
Inorganic clays of medium to high plasticity, sandy fat clay,
or gravelly fat clay
Organic
OHOrganic
clays of medium to high plasticity, organic silts
HIGHLY ORGANIC
SOILS
Primarily organic matter, dark in color,
and organic odor
PT
Peat, humus, swamp soils with high organic content (ASTM D4427)
Classification of Soil Constituents
MAJOR constituents compose more than 50 percent,
by weight, of the soil. Major constituents are capitalized
(i.e., SAND).
Minor constituents compose 12 to 50 percent of the soil
and precede the major constituents (i.e., silty SAND).
Minor constituents preceded by "slightly" compose
5 to 12 percent of the soil (i.e., slightly silty SAND).
Trace constituents compose o to 5 percent of the soil
(i.e., slightly silty SAND, trace gravel).
Relative Density
(Coarse Grained Soils)
Consistency
(Fine Grained Soils)
N, SPT,
Relative
N, SPT,
Relative
Blows/FT
Density
Blows/FT
Consistency
0-4
Very loose
Under 2
Very soft
4 -10
Loose
2-4
Soft
10 - 30
Medium dense
4-8
Medium stiff
30 - 50
Dense
8 -15
Stiff
Over 50
Very dense
15 - 30
Very stiff
Over 3o
Hard
Grain Size Definitions
Description
Sieve Number and/or Size
Fines
<#200 (o.o8 mm)
Sand
-Fine
#200 to #40 (o.o8 to 0.4 mm)
-Medium
#40 to #10 (0.4 to 2 mm)
-Coarse
#10 to #4 (2 to 5 mm)
Gravel
-Fine
#4 to 3/4 inch (5 to 19 mm)
-Coarse
3/4 to 3 inches (19 to 76 mm)
Cobbles
3 to 12 inches (75 to 305 mm)
Boulders
>12 inches (305 mm)
1 Moisture Content Definitions 1
Dry Absence of moisture, dusty, dry to the touch
Moist Damp but no visible water
Wet Visible free water, from below water table
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
Soil Classification Chart
Figure Ci
(2o6) 331-1097
_
www.cobaltgeo.com
cobaltgeo(&gmail.com
Test Pit TP-1
Date: August 2022
Depth. 8'
Groundwater: None
Contractor: Jim
Elevation:
Logged By: PH
Checked By: SC
N
JO
o
Q
Moisture Content (%)
Plastic I / Liquid
U
E
3
Limit
Limit
}
�
t
0
N
Material Description
DCP Equivalent N-Value
Q
a)?
o
O
0 10
20 30 40 50
Topsoil/Vegetation_________________________________
1
SM
Loose to medium dense, silty -fine to medium grained sand trace
gravel, reddish brown to yellowish brown, dry to moist.
2
(Weathered Advance Outwash)
3
------
4
---
--
SP
---------------------------------------------
Medium dense to dense, fine to medium grained sand trace silt trace
gravel, grayish brown, moist. (Advance Outwash)
5�
6
Local caving
7
End of Test Pit 8'
9
10
Cobalt Geosciences, LLC
Proposed Residence
P.O. Box 82243
COBALT
1050 Walnut Street
Test Pit
Kenmore, WA 98028
(2o6) 331-1097
=-G E 0
S C I
E N C E S
Edmonds, Washington
Logs
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cobaltgeo(digmail.com