RESUB1 BLD2021-0428+GEO EVALUATION+5.7.2021_4.51.08_PM+2186095COBALT
G E 0 S C I E N C E S
April 20, 2021
Updated April 26, 2021
Sam Siow Fong
Samsf2Ca yahoo.com
RE: Limited Geotechnical Evaluation
Proposed Additions
18416 Olympic View Drive
Edmonds, Washington
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, Washington 98028
In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to
discuss the results of our limited geotechnical evaluation at the referenced site.
In preparation of this report, we have visited the site, reviewed provided plans by Ryan Rhodes
Designs dated March 24, 2021, and reviewed a geotechnical report for this property by The Galli
Group dated July 31, 2007.
Site and Project Description
The site is located at 18416 Olympic View Drive in Edmonds, Washington. The site consists of
one irregularly shaped parcel (No. 00565600200301) with a total area of about 0.46 acres.
The central portion of the property is developed with a single-family residence with daylight
basement, patio areas, driveway, and landscaped regions. The remainder of the property is
vegetated with grasses, bushes, shrubs, and variable diameter trees. There are local boulder
groupings up to 3 feet tall placed as landscaping systems (not rockery walls) near the southwest
building corner. There is a rockery near the southwest corner of the property, supporting cuts
above an existing driveway.
The site slopes downward from east to west at magnitudes of 5 to 6o percent and total relief of
about 45 feet. The steeper slopes are located west of the residence, just above an existing paved
driveway that accesses homes to the west.
The property is bordered to the north, south, and west by residential properties and to the east by
Olympic View Drive.
The project includes local additions to the residence. These will be located along the
southwestern side of the building, in areas that are currently developed with the structure, decks,
and patio areas. The additions include enclosing a portion of existing exterior space, new patio
areas, and new decks. Grading will include limited cuts and fills, and foundation loads will
generally be light if any new foundation elements are proposed.
Area Geology
The Geologic Map of the Edmonds East and West Quadrangles indicates that the site is underlain
by Vashon Recessional Outwash.
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These outwash deposits include gravelly sands and poorly graded sands with gravel. These
deposits are typically medium dense to dense and coarse grained. In this area, the recessional
outwash is likely underlain by a zone of Vashon Advance Outwash and at depth by Transitional
Beds and older pre-Vashon deposits. All of these materials are typically dense to very dense
below a weathered zone.
Soil & Groundwater Conditions
As part of our evaluation, we reviewed previous borings by Galli Group and excavated an
additional hand boring to verify the soil conditions near the proposed project. Our hand boring
encountered a thin layer of topsoil underlain by about 3.5 feet of medium dense fill. The fill was
underlain by dense, fine to medium grained sand (Outwash), which continued to the termination
depth of the hand boring.
The Galli Group borings (attached) encountered fill near the top of the slope underlain by dense
outwash or till -like materials. Their other boring at the toe of the slope encountered relatively
dense outwash-like materials.
Steep Slope/Landslide Hazards
The site and adjacent areas contain steep slope/landslide hazard areas and associated buffer
zones.
The site slopes downward from east to west at magnitudes of 5 to 6o percent and total relief of
about 45 feet. The steeper slopes are located west of the residence, just above an existing paved
driveway that accesses homes to the west. The steeper slopes have variable magnitudes above 40
percent and are heavily vegetated.
The site slopes have been modified historically, likely made slightly steeper than the former,
natural slope in this area through cuts and fill placement. Overall, the steep slope and other
nearby slopes appear stable at this time with no evidence of instability or erosion.
The project consists of very limited work within already developed areas. This work will not
decrease slope stability or pose an unreasonable threat to persons or property on the site or
adjacent areas provided the earthwork and grading activities are periodically monitored by the
geotechnical engineer and performed according to the plans and this report.
Erosion Hazard
The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that
the east half of the property is underlain by Alderwood gravelly sandy loam (15 to 30 percent
slopes). These soils can have severe and very severe erosion potential when exposed on slope
magnitudes greater than about 15 percent. These soils are included in the Edmonds Municipal
Code section 23.80.020 under Al. It is our opinion that typical erosion control measures will be
suitable to limit/reduce erosion potential during the water meter and any limited driveway
grading.
It is our opinion that soil erosion potential at this project site can be reduced through landscaping
and surface water runoff control. Typically, erosion of exposed soils will be most noticeable
during periods of rainfall and may be controlled by the use of normal temporary erosion control
measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The
typical wet weather season, with regard to site grading, is from October 31st to April 1st. Erosion
control measures should be in place before the onset of wet weather.
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Code Information
23.80.o6o Development standards — General requirements.
A. Alterations of geologically hazardous areas or associated buffers may only occur for activities
that:
1. Will not increase the threat of the geological hazard to adjacent properties beyond
predevelopment conditions;
2. Will not adversely impact other critical areas;
3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or
less than predevelopment conditions; and
4. Are certified as safe as designed and under anticipated conditions by a qualified engineer or
geologist, licensed in the state of Washington.
The currently proposed project includes minimal grading and other surface work within already
developed areas near the top of a steep slope. It is our opinion that this work will not affect global
or local stability provided work is monitored by the geotechnical engineer and erosion control
measures are in place during construction.
The proposed water meter relocation work will not increase the threat of geologic hazards on
adjacent properties, will not impact other critical areas, and are safe as designed under
anticipated conditions.
23.80.07o Development standards — Specific hazards.
A. Erosion and Landslide Hazard Areas. Activities on sites containing erosion or landslide
hazards shall meet the requirements of ECDC 22.80.o6o, Development standards — General
requirements, and the specific following requirements:
1. Minimum Building Setback. The minimum setback shall be the distance required to ensure the
proposed structure will not be at risk from landslides for the life of the structure, considered to be
120 years, and will not cause an increased risk of landslides taking place on or off the site. A
setback shall be established from all edges of landslide hazard areas. The size of the setback shall
be determined by the director consistent with recommendations provided in the geotechnical
report to eliminate or minimize the risk of property damage, death, or injury resulting from
landslides caused in whole or part by the development, based upon review of and concurrence
with a critical areas report prepared by a qualified professional;
The project is within the current developed layout at the site. The current building setbacks from
the steep slope appear suitable provided any new foundation elements are supported on medium
dense or firmer native soils or on driven pipe piles extending through any fill. We recommend a
minimum effective setback of at least 10 feet for the residential structure and at least 3 feet for
new deck footings. The effective setback is the horizontal distance measured from the base of the
foundation closest to the slope to the face of the adjacent slope. By deepening footings an
effective setback can be increased.
Alternatively, new footings could be supported on driven pipe piles extending to refusal in the
underljng dense native soils. If this is performed, the foundations may be located as proposed
without additional setbacks. These footings should be embedded the typical minimum required
depths (1.5 feet).
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2. Buffer Requirements. A buffer may be established with specific requirements and limitations,
including but not limited to, drainage, grading, irrigation, and vegetation. Buffer requirements
shall be determined by the director consistent with recommendations provided in the
geotechnical report to eliminate or minimize the risk of property damage, death, or injury
resulting from landslides caused in whole or part by activities within the buffer area, based upon
review of and concurrence with a critical areas report prepared by a qualified professional;
The site currently fully developed. No specific buffer is required for the current project beyond
what is currently_ present. The area at the top of the slope has a distinct break where existing
development features begin. This distance/location should be maintained for the proposed
development. To our knowledge, the new work is within already developed areas.
3. Alterations. Alterations of an erosion or landslide hazard area, minimum building setback
and/or buffer may only occur for activities for which a hazards analysis is submitted and certifies
that:
a. The alteration will not increase surface water discharge or sedimentation to adjacent properties
beyond predevelopment conditions;
b. The alteration will not decrease slope stability on adjacent properties; and
c. Such alterations will not adversely impact other critical areas;
Provided earthwork activities are performed in accordance with the approved plans, all runoff is
fully controlled, and periodic geotechnical oversight is performed, the development will not
decrease slope stability on adjacent properties, will not increase surface water discharge or
sedimentation beyond current levels, and will not impact other critical areas. Temporary and
permanent erosion and sediment control devices should be in at all times during construction.
The slopes themselves will not be disturbed or graded.
4. Design Standards within Erosion and Landslide Hazard Areas. Development within an erosion
or landslide hazard area and/or buffer shall be designed to meet the following basic requirements
unless it can be demonstrated that an alternative design that deviates from one or more of these
standards provides greater long-term slope stability while meeting all other provisions of this
title. The requirement for long-term slope stability shall exclude designs that require regular and
periodic maintenance to maintain their level of function. The basic development design standards
are:
a. The proposed development shall not decrease the factor of safety for landslide occurrences
below the limits of 1.5 for static conditions and 1.2 for dynamic conditions. If stability at the
proposed development site is below these limits, the proposed development shall provide
practicable approaches to reduce risk to human safety and improve the factor of safety for
landsliding. In no case shall the existing factor of safety be reduced for the subject property or
adjacent properties;
b. Structures and improvements shall be clustered to avoid geologically hazardous areas and
other critical areas;
c. Structures and improvements shall minimize alterations to the natural contour of the slope,
and foundations shall be tiered where possible to conform to existing topography;
d. Structures and improvements shall be located to preserve the most critical portion of the site
and its natural landforms and vegetation;
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e. The proposed development shall not result in greater risk or a need for increased buffers on
neighboring properties;
f. The use of retaining walls that allow the maintenance of existing natural slope area is preferred
over graded artificial slopes; and
g. Development shall be designed to minimize impervious lot coverage;
The very limited project scope does not pose a risk to critical areas or the need to increase buffers
on adjacent properties. Essentially, the current stability will not be affected by the proposed
construction since the loads are approximately equal to what is currently_ present.
5. Vegetation Retention. Unless otherwise provided or as part of an approved alteration, removal
of vegetation from an erosion or landslide hazard area or related buffer shall be prohibited;
6. Seasonal Restriction. Clearing shall be allowed only from May 1st to October ist of each year;
provided, that the director may extend or shorten the dry season on a case -by -case basis
depending on actual weather conditions, except that timber harvest, not including brush clearing
or stump removal, may be allowed pursuant to an approved forest practice permit issued by the
city of Edmonds or the Washington State Department of Natural Resources;
7. Point Discharges. Point discharges from surface water facilities and roof drains onto or
upstream from an erosion or landslide hazard area shall be prohibited except as follows:
a. Conveyed via continuous storm pipe downslope to a point where there are no erosion hazard
areas downstream from the discharge;
b. Discharged at flow durations matching predeveloped conditions, with adequate energy
dissipation, into existing channels that previously conveyed storm water runoff in the
predeveloped state; or
c. Dispersed discharge upslope of the steep slope onto a low -gradient, undisturbed buffer
demonstrated to be adequate to infiltrate all surface and storm water runoff, and where it can be
demonstrated that such discharge will not increase the saturation of the slope; and
We concur with the above code items and have no additional comments at this time.
Seismic Parameters
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
stiff/medium dense soils within the upper ioo feet.
We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to
obtain values for Ss, S,, F,,, 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 ASCE 7-io and 7-16.
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Seismic Design Parameters (ASCE 7-10)
Site
Spectral
Spectral
Site
Design Spectral
Design
Class
Acceleration
Acceleration
Coefficients
Response Parameters
PGA
at 0.2 sec. (g)
at 1.o sec. (g)
Fa
F-,
SDs
SM
D
1.286
0.504
1.0
1.5
0.857
0.504
0.524
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 1.o sec. (g)
Fa
F-,
SDs
SD1
D
1.299
0.459
1.0
Null
0.866
Null
0.555
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. "Null" indicates see Section
11.4.8 of the ASCE.
Conclusions and Recommendations
General
The area of the project is underlain by local fill and at depth by dense outwash and/or till. The
proposed additions 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. Overexcavation of any fill is
required below new footings. Driven pipe piles may be used to support new foundation elements
in lieu of overexcavation and replacement.
If new footings are proposed, the following recommendations apply: Any new footings for
residential spaces should be set back at least 10 feet from the top of moderately steep slope areas.
Accessory decks should be set back at least 3 feet from the top of the slope. Footings may be
deepened in order to create effective setbacks equal to these distances. The effective setback is
the horizontal distance from the closest footing edge to the adjacent slope face.
Alternatively, new footings could be supported on driven pipe piles. If pipe piles are used to
support the footings, the effective setback requirement is not necessary and the proposed
building/improvement locations are acceptable as shown on the current plans. The pipe piles will
likely extend 10 to 20 feet below grade, thereby resulting in adequate setbacks for the overall
foundation system. New footings bearing on pipe piles driven to refusal may have typical
embedments (1.5 feet).
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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
where root systems can extend to greater depths, in areas of existing foundation systems, and in
any areas underlain by undocumented fill. We do not anticipate significant grading or soil
removal/
The native soils consist of sand with gravel and silt, and silty -sand with gravel. 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 2 feet or less for foundation and utility placement. Any deeper
temporary excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose
native soils and fill and 1H:1V in medium 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.
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.
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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.
Stormwater Management
We recommend that all collected runoff from impervious surfaces be routed to City infrastructure
or another system that does not discharge on or above any steep slopes.
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.
Foundation Design
Any new foundation elements may be supported on shallow spread footings bearing on
undisturbed medium dense or firmer native soils or on properly compacted structural fill placed
on the suitable native soils. Any undocumented fill should be removed and replaced with
structural fill below foundation elements. Structural fill below footings should consist of clean
angular rock 5/8 to 2 inches in size.
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 2,000
pounds per square foot (psf) may be used for design.
If pin piles are utilized, they may consist of 2 inch diameter Schedule 8o galvanized steel pipes.
Refusal criteria is 3 cycles of 6o seconds per inch of penetration and an axial load of 3 tons per
pile 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
0.4o acting between the base of foundations and the supporting subgrades. Lateral resistance for
footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds
per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12
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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.
Slab -on -Grade
We recommend that the upper 12 inches of the existing fill and/or native soils within slab areas be
re -compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method).
Overexcavation of poor quality soils, including silt/clay and/or highly organic soils, will be
required to variable depths if they are present. The geotechnical engineer should observe slab
excavations to determine the depth of overexcavation.
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 302JR-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 18o pounds per cubic
inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and
compacted as outlined in Section 8.1. A minimum 4 inch thick capillary break should be placed
over the prepared subgrade. These materials should consist of 5/8 inch clean angular rock or pea
gravel.
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:
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• 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.
Closure
The information presented herein is based upon professional interpretation utilizing standard
practices and a degree of conservatism deemed proper for this project. We emphasize that this
report is valid for this project as outlined above and for the current site conditions and should not
be used for any other site.
Sincerely,
Cobalt Geosciences, LLC
ZONAL
4/26/2021
Phil Haberman, PE, LG, LEG
Principal
PH/sc
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YY4
Approximate Boring and Hand Boring Locations N
B-1 Borings by Galli Group (200 7)
HB-1 A
Effective Setback Pin Pile Support Option
D
Deepen Footing
to Achieve
Setback Distance
(D)
/Plan Location/
Distance from
Slope
Proposed Additions SITE PLAN
18416 Olympic View Drive
Edmonds, Washington FIGURE i
Driven Pipe Piles
to Refusal
Cobalt Geosciences, LLC
P.O. Box 82243
Kenmore, WA 98028
(2o6) 331-1097
www.cobaltgeo.com
cobaltgeoogmail.com
Unified Soil Classification System (USCS)
MAJOR DIVISIONS SYMBOL
TYPICAL DESCRIPTION
GW
Clean Gravels
Well -graded gravels, gravels, gravel -sand mixtures, little or no fines
Gravels
(more than 50%
(less than 5% _ GP
fines)
Poorly graded gravels, gravel -sand mixtures, little or no fines
COARSE
GRAINED
SOILS
of coarse fraction
retained on No. 4
sieve)
GM
Gravels with
Fines
(more than 12% GC
fines)
Silty gravels, gravel -sand -silt mixtures
Clayey gravels, gravel -sand -clay mixtures
(more than 50%
retained on
;°e sw
Clean Sands
Well -graded sands, gravelly sands, little or no fines
No. 200 sieve)
Sands
(50% or more
of coarse fraction
(less than 5% SP
fines)
Poorly graded sand, gravelly sands, little or no fines
passes the No. 4
sieve)
sM
Sands with Fines
Silty sands, sand -silt mixtures
(more than 12% sc
fines)
Clayey sands, sand -clay mixtures
ML
Inorganic silts of low to medium plasticity, sandy silts, gravelly silts,
FINE GRAINED
SOILS
(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
oL
Organic
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 CH
elastic silt
Inorganic clays of medium to high plasticity, sandy fat clay,
or gravelly fat clay
OH
Organic
Organic clays of medium to high plasticity, organic silts
HIGHLY ORGANIC
SOILS
primarily organic matter, dark in color, PT
and organic odor
Peat, humus, swamp soils with high organic content (ASTM D4427)
1 Classification of Soil Constituents 1
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 (0.08 mm)
Sand
-Fine
#200 to #40 (0.08 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)
Moisture Content Definitions
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, WA98028 Soil Classification Chart Figure C1
(206) 331-1097
_ www.cobalt eg o.com
cobaltgeo(d-) gmail.com
Log of Hand Boring
HB-1
Date:
April 2021
Depth: 9'
Initial Groundwater: N/A
Contractor:
Elevation: N/A
Sample Type: Grab
Method: Hand Auger
Logged By: PH Checked By: SC
Final Groundwater: N/A
o-a
Q
Moisture Content (�)
Plastic 1 Liquid
O
zo
o
a
Material Description
3
Limit Limit
DCP Equivalent N-Value
o
m
?
o
O
0 10 20 30 40 501
Vegetation/Topsoil
---
----
---
w --
---
--------------------------------------------
.+ -
SP/
Medium dense, silty -fine to medium grained sand
SM
trace gravel, yellowish brown to grayish brown,
moist. (Fill)
2
.5
'hy
3
...
SP
---------------------------------------------
Medium dense to dense, fine to medium grained sand trace gravel,
ti
grayish brown, moist. (Advance Outwash?)
5
b
8
1 y
End of Hand Boring 9'
10
Cobalt Geosciences, LLC
Proposed Additions Hand Ken Box
Kenmore,, WA WA 98028
_C 0 BA LT 18416 Olympic View Drive Boring (2o6) 331-1097
G E • S C I E N C k S Edmonds, Washington Log www.cobaltgeo.com
cobaltgeoogmail.com
i
prai'ect 1474 - 01 Boring Log B-1
Elevation _ 98.5 fee
Soil Description
Loose, dark brown, silty sand w/ trace small gravel
(FILL)
Brown, silty fine SAND w/ trace fine gravel,
v moist
Dense, verysilty SAND w/ trace fine gravel,
wet in top 2" (GLACIAL OUTWASH)
Brown, silty SAND w/ trace gravel
m Mer added at 12'
---------------------------------
Very dense, brown, silty SAND w/ trace gravel,
moist
N R gni ince on rock
Bottom of boring at 15.5' depth
No water encountered in boring
Boring located 5' west of pool at
top of bank
•
5'
10,
15'
25'
39
35'
40'
I12-23-23
I18-21-22
= 50 / 5.5"
_ 1 50+
6-25-2007
The Galli Group
Geotechnical Consulting 18416 Olympic View Dr. Fi ure A-2
5034 -18th Avenue NE Edmonds, Washington g
Prefect 1474 - 01
Boring Log B-2
6-25-2007
The Galli Group 18416 Olympic View Dr.
Geotechnical Consulting Figure A-3
5034 - 18th Avenue NE Edmonds, Washington
c-olia %A14 9R1 n5