REVIEWED PLN BLD-BLD2021-0651+Geotechnical_Report+5.10.2021_3.25.45_PM+2188516Group Northwest, Inc.
April 20, 2021
Spencer Franks
8732 209th Place SW
Edmonds, Washington 98026
Email: spencerfkpennonconstruction.com
staceesandbergkemail. com
RECEIVED
Subject: Geotechnical Engineering Study
Proposed Block Retaining Wall
8732 209th Place SW
Edmonds, Washington 98026
Dear Mr. Franks,
May 11 2021
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
1:3��7�•I�y�iQ:Is�il
Geolechnical Engineers, Geologists
& Environmental Specialists
G-5412
..,.,.,.,.,.,...............................
REVIEWED
BY
CITY OF EDMONDS
BUILDING DEPARTMENT
GEO Group Northwest, Inc. has completed a geotechnical engineering study of the above -
subject property for the proposed retaining walls in Edmonds, Washington. The scope of our
services included a review of the area geologic map, soil boring logging, geologically hazardous
areas evaluation, block retaining wall design, and the completion of this report.
SITE DESCRIPTION
The project site is located in northern Edmonds, Washington, as illustrated in Plate 1 — Site
Location Map. The property is 0.22 acres in size, rectangular in shape, and is accessible to the
east by a common driveway that extends southward from 209th Place SW and is shared with the
adjacent north and south properties. The property was originally developed in 1969 to include a
single-family residence that contains a single story and an east -facing daylight basement. The
residence contains approximately 2,600 square feet of interior living space between the two
floors as well as an attached 480 square -foot two -car garage adjacent to the main floor's north
perimeter. The west section of the property contains relatively flat topography, while the south
13705 Bel -Red Road • Bellevue, Washington 98005
Phone 425/649-8757 • Fax 425/649-8758
April 20, 2021 G-5412
8732 2091h Place SW Edmonds, Washington Page 2
side yard gradually slopes to the eastern back yard area. The east backyard area contains the top
of a southeast -facing steep slope area with a height of about 20 feet extending towards the
southeast property corner. Beyond the property line, the slope continues to descend another 20
vertical feet towards Pioneer Way to the southeast. The southeast area of the sloped backyard is
mostly undeveloped, though the northern topography of the backyard area contains previously
constructed at -grade concrete steps that closely follow the existing contours of the slope. The
existing conditions of the above -subject property are illustrated in Plate 2 — Site Plan.
According to the City of Edmonds GIS Maps, the easternmost section of the property is mapped
as being located within a landslide hazard area containing slopes with grades surpassing 40%.
The northeast area of the property is also mapped as an erosion hazard area and the south to
southwest portion of the property is mapped as a severe erosion hazard area, with both
designations defined as containing slope inclinations between 15 and 40%.
PROPOSED BLOCK RETAINING WALLS
Based on the information provided, we understand that you are proposing to redevelop the
existing landscaped area located along the southwest and south property lines to include new
block retaining walls with a maximum height of 3 to 4 feet. The new walls will extend into the
south side yards, where the topography begins to descend eastward, but is not planned to
encroach within the landslide hazard area or a proposed horizontal setback distance of 15 feet
from the top of the slope. The eastern section of the proposed retaining wall will include
gradually descending heights that will reach the existing grade of the side yard area.
The maximum 3 to 4-foot height of the proposed retaining wall will be concentrated near the
west property line, where we understand you are proposing to fill in the existing topography to
partially reduce the slope and provide additional erosion control in the front yard area south of
the residence's driveway and west of the residence. The north -south segment of the retaining
wall is not planned to be constructed adjacent to the shared access road located 15 feet north of
the southwest property corner. The existing southwest area of the property contains a south -
facing rockery, existing trees, and other previously constructed landscaping, and we understand
that these items are proposed to be removed by the new retaining wall as well. We also
understand that you are proposing to replace the existing concrete walkway west of the residence
and south of the driveway with permeable concrete pavers. The approximate geometry of the
proposed new block retaining walls is illustrated in Plate 3 —Proposed Retaining Wall Design.
GEO Group Northwest, Inc.
April 20, 2021 G-5412
8732 2091h Place SW Edmonds, Washington Page 3
GEOLOGIC OVERVIEW
According to published geologic mapping of the areal, the project site is characterized as being
underlain with Glacial till (Qvt) from the Fraser Glaciation. Vashon till deposits typically consist
of non -stratified mixtures of sand, silt, and gravel that were deposited beneath the sole of the
Vashon glacier as it advanced southward into the Puget Sound area approximately 15,000 years
ago. As a result of being consolidated by the glacial ice, these deposits are typically dense to
very dense and relatively impermeable.
SUBSURFACE INVESTIGATION
On March 29, 2021, Mr. Bryce Frisher, Staff Geotechnical Engineer from our firm, visited the
site to perform a visual reconnaissance of the property and investigate the subsurface soil
conditions. We drilled two exploratory borings (HA-1 and HA-2) using a hand auger during our
site visit. HA-1 was conducted near the top of the existing rockery near the south property line,
and HA-2 was conducted to the west of the top of the steep slope area. Locations of our
exploratory soil borings are shown in Plate 2 —Site Plan. Logs of the conditions encountered in
the borings are provided in Attachment 1 to this report.
Soils encountered in HA-1 consisted of a surficial layer of dark brown, fine-grained loose sand
with silt underlain with loose, brown silty sand and topsoil material with thin roots and gravel to
a depth of about 2 feet below the existing ground surface. Soils below 2 feet consisted of
similarly loose, brown, moist fine-grained silty sand with gravel to a depth of 4 feet below the
ground surface. Soils below 4 feet consisted of medium dense, brown to grayish light brown
fine-grained sand with gravel to a depth of 5 feet, where the boring was terminated. Water
seepage was not encountered at this boring.
Soils encountered in HA-2 consisted of a surficial layer of brown to grayish brown, loose sand
underlain with medium dense, grayish brown to light brown fine-grained sand with silt to a depth
of about 1 foot below the existing ground surface. Soils below 1 foot consisted of medium dense
to dense, fine-grained grayish brown sand with some silt and gravel to a depth of 2 feet below
the ground surface, where the boring was terminated due to refusal. We did not encounter water
' Geologic Map of the Edmonds East and part of the Edmonds West quadrangles, Washington, Minard, J.P., 1983,
U.S. Geological Survey, Miscellaneous Field Studies Map MF-1541.
GEO Group Northwest, Inc.
April 20, 2021 G-5412
8732 2091h Place SW Edmonds, Washington Page 4
seepage in this boring. The soils encountered in this boring were consistent with the Vashon till
deposits in the geologic mapping of the area.
GEOLOGICALLY HAZARDOUS AREAS REVIEW
According to the City of Edmonds GIS Webmap, the above -subject property is mapped as
containing two geologically hazardous areas. The southern half of the property which contains
the existing residence and pre -developed side yard landscaping is located within a severe erosion
hazard with slopes between 15-40%, while the eastern undeveloped sloped portion of the
property is located within a landslide hazard area with slopes of 40% and greater. The
geologically hazardous areas mapping is illustrated in Plate 4 — Hazard Areas Mapping.
The City of Edmonds prohibits the construction of retaining walls of any height within a
geologically hazard areas other than soil erosion hazard areas as defined by Chapter 23.80 of the
Edmonds City Code and Community Development Code (ECDC). Based on the proposed plans
provided, we understand that the landscape design will be constructed within the soil erosion
hazard area and not within the landslide hazard area depicted by the GIS maps.
Soil Erosion Hazard
The east portion of the residence and its southern side yard are located within a severe soil
erosion hazard area, as shown in the GIS data. The Development Standards as described in
23.80.060 and 23.80.070 of the ECDC state that alterations or activities on sites containing
erosion or landslide hazards may only occur if the activities will not increase the threat of the
geological hazard to adjacent properties or adversely impact other critical areas, and are designed
so that the hazard is eliminated or mitigated. Furthermore, setback and buffer requirements will
be determined by the director consistent with the geotechnical engineer's assessment of the slope
stability and the hazard mitigation recommendations provided in the geotechnical report.
During our site reconnaissance and subsurface investigation, we encountered medium dense to
dense, fine-grained grayish brown sand at a depth of 2 feet below the ground surface in HA-2
near the top of the steep slope area. The soils encountered in HA-1 consisted of 4 feet of loose,
fill -like soils underlain with medium dense, grayish light brown sand and gravel. In our opinion,
these soils are suitable for supporting the proposed retaining wall as illustrated in the design
plans. The retaining wall will be located within a gradually sloped area that contains previously
GEO Group Northwest, Inc.
April 20, 2021 G-5412
8732 2091h Place SW Edmonds, Washington Page 5
developed landscaping and will not be designed to support any surcharge loads or unstable
slopes. It is our opinion that the new retaining wall will not increase the risk of soil erosion at
the property or the adjacent properties.
In its existing condition, the landscape throughout the south side yard does not contain evidence
of slope instability. The exposed concrete foundations along the exterior south and east
residence perimeter did not contain visible cracks or signs of previous settlement. The proposed
block retaining wall will closely follow the natural contours of the gradual slope throughout the
southern side yard of the property by replacing the existing rockery and other previously
installed landscaping. The block retaining wall will be located within a relatively flat section of
the soil erosion area, where the total declination within the length of the proposed wall is
approximately 4 vertical feet.
Landslide Hazard
The eastern section of the property contains a steep slope with inclinations of 40% or greater and
a vertical height change of approximately 20 feet. This slope extends from the location of the
residence's east deck area towards the east property line and has remained generally
undeveloped since the original construction of the above -subject property's residence in 1969.
The steep slope area does contain a series of at -grade concrete steps that descend approximately
15 feet down the northern area of the slope before ending about 10 horizontal feet from the east
property line. The proposed new block retaining wall does not include any development within
this slope and the general landslide hazard area. The existing vegetation within the landslide
hazard is not proposed to be altered or removed during construction.
During our site reconnaissance, we observed the existing condition of the landslide hazard area
by probing the soils with a 0.5-inch diameter probing rod. The mature trees located within the
steep slope area are near -vertical. While probing the steep slope area, we encountered dense
soils within one to two feet of the existing ground surface. Based on our site reconnaissance and
our understanding of the site soils, it is our opinion that the landslide hazard area is stable in its
existing condition.
The proposed new block retaining wall is planned to occur within the previously developed south
and west sections of the property, as shown in Plate 3 —Proposed Retaining Wall Design. This
area of the property is located within topographies with inclinations between 15 and 40% and
GEO Group Northwest, Inc.
April 20, 2021 G-5412
8732 2091h Place SW Edmonds, Washington Page 6
therefore not within the landslide hazard area to the east of the residence. We understand that the
proposed new block retaining is planned to be located within the minimum 50-foot buffer from
the top of the landslide hazard area. In our opinion, the required buffer from the top of the steep
slope can be reduced to a minimal distance of 15 feet, suitable for the proposed scope of work
due to the slope stability we encountered during our reconnaissance.
Geologically Hazardous Areas Conclusions
In our opinion, the geologically hazardous areas at the project site are stable in their existing
conditions. We did not encounter any evidence of landslide debris within the landslide hazard
area, and the soils encountered during our subsurface exploration consisted of an upper layer of
rockery backfill material underlain with medium dense to dense, native fine-grained sands
suitable for supporting the proposed new block retaining wall. It is our opinion that the proposed
retaining wall achieves the minimal amount of new impervious area in the plans, as required in
the ECDC design standards. We understand that the eastern section of the new retaining wall is
proposed to be constructed within the 50-foot buffer from the top of the steep slope landslide
hazard area. In our opinion, the buffer may be reduced to a minimum distance of 15 feet without
adversely impacting the slope's stability at the project site or at the adjacent properties.
Reducing the buffer will not adversely impact the soil erosion hazard at the proposed retaining
wall location or the adjacent landslide hazard area to the east.
The new retaining wall and subsequent backfilling are designed so that they minimize the
alterations to the existing contours along the south side yard of the residence. The proposed
retaining wall also fully preserves the steep slope and landslide hazard area east of the residence,
the most critical portion of the site, as required by the ECDC. The location and height of the
proposed new retaining wall within the soil erosion hazard area will not adversely impact the
adjacent landslide hazard area, in our opinion. The removal of the existing trees within the
development area will also not pose an adverse risk to the nearby erosion and landslide hazards
present at the property. Based on the plans provided and our understanding of the project site, we
conclude that the proposed new retaining wall and permeable pavers will not adversely impact
the soil erosion and landslide hazard areas that have been mapped at the above -subject property,
and that the risk of damage to the adjacent properties will be minimal, provided that the
recommendations and retaining wall design requirements outlined in this geotechnical report are
properly implemented during construction.
GEO Group Northwest, Inc.
April 20, 2021
8732 2091h Place SW Edmonds, Washington
CONCLUSIONS AND RECOMMENDATIONS
G-5412
Page 7
It is our opinion that the proposed new block retaining wall as described in this report can be
accomplished so that it does not increase the risk of soil instability at the site or at the adjacent
properties. The underlying soil erosion hazard at the south side yard area will not be
significantly impacted by the proposed retaining walls and removal of the existing trees, as the
encountered soils consist of fill -like material and not loose, unstable landslide debris. The
retaining wall can be supported on a layer of crushed rock that bears directly on the underlying
medium dense to dense soils. Details of these recommendations and other recommendations
regarding geotechnical aspects of the project are presented in the following sections of this
report.
Grading and Earthwork
Site Clearing and Erosion Control
Grading work for the proposed retaining wall should be restricted to the minimum needed to
achieve proposed final grades. The area where construction work will be performed should be
cleared of the existing trees within the development area, vegetation, topsoil, organics, debris,
and any other deleterious materials that are found. These materials should be hauled off site or
used for landscaping, as appropriate; they should not be used as structural fill or retaining wall
backfill for the project.
Temporary erosion and sedimentation controls (TESCs) such as silt fences should be installed as
part of site clearing activities. The silt fences or other barrier controls should be placed along the
south and west property lines as well as the cross -slope boundaries of the disturbed areas to
prevent sediment -laden runoff from being discharged off site. Exposed soils, including
stockpiled soils, should be covered with plastic sheeting when they are not being worked.
Excavations and Slopes
Temporary excavation slopes should not be greater than the limits specified in local, state and
federal government safety regulations. Based on the findings from our subsurface investigation,
water seepage should not be anticipated for excavations up to 4 feet below the existing ground
surface. If water seepage or other adverse conditions are encountered, temporary cuts in these
GEO Group Northwest, Inc.
April 20, 2021
8732 2091h Place SW Edmonds, Washington
G-5412
Page 8
soils may need to be made at shallower inclinations where recommended by the geotechnical
engineer.
During construction, water should not be allowed to stand in areas where the risers are to be
constructed. Surface runoff should not be allowed to flow over the top of slopes into
excavations. During wet weather, exposed slopes should be covered with plastic sheeting to
prevent erosion or softening.
Subgrade Preparation
Soils in areas to receive the crushed rock subgrade should be prepared to a firm, unyielding
condition. The prepared subgrade should be observed and approved by the geotechnical
engineer. Any detected soft spots or disturbed areas should be compacted or excavated and
replaced with compacted structural fill or crushed rock as directed by the geotechnical engineer.
Proposed Block Retaining Wall
Based on the information provided, we understand that the proposed block retaining wall will
have a maximum height of 3 to 4 feet near the southwest property corner, and this height will
gradually step down with the topography along the south side yard. The north -south segment of
the retaining wall will extend approximately 15 feet to the north from the southwest property
corner adjacent to the private driveway. This segment of the retaining wall will not be
constructed adjacent to the shared access road to the north. The east -west segment will extend
approximately 35 feet to the east from the southwest property corner. The east -west segment of
the wall will have heights ranging between 1 and 4 feet, depending on the adjacent sided yard
topography. It is our opinion that concrete blocks (6" H x 16" L x 12" D, or similar dimensions)
are sufficient to achieve the proposed wall geometry. To prevent erosion, there must be at least
one buried block extended into the ground surface along the entire length of the new retaining
wall sections.
The block retaining walls require a crushed rock (1/4 to 1.5 inches diameter and with less than
5% fines) base with a minimum depth of 6 inches or thicker, depending on the presence of soft
soils during excavations. The same material must be used to a minimum 12 inch layer behind
the base and the stacked blocks up to a depth of one block (8 inches) below the ground surface.
GEO Group Northwest, Inc.
April 20, 2021 G-5412
8732 2091h Place SW Edmonds, Washington Page 9
The top 12 inches of the fill behind the walls can consist of topsoil if desired. This material can
be separated from the underlying more granular drainage material by a geotextile fabric. Typical
section details of the proposed block retaining wall are illustrated in Plate 3 — Proposed
Retaining Wall Design.
Surface Drainage
Storm water should not be permitted to develop into concentrated flows on the ground surface,
because concentrated flows can lead to increased soil erosion and rutting. Final site grades
within the construction area should direct surface water away from the residence to mitigate the
landslide and soil erosion hazards located at the east section of the property.
Subsurface Drainage
We recommend that a zone of crushed rock backfill material at least 12 inches wide and
consisting of (1/4 to 1.5-inches diameter and with less than 5% fines) should be placed against
the full height of the block retaining wall sections. This backfill should extend downward to the
bottom of the retaining wall and at least 6 inches below the base of the wall, as shown in Plate 3
— Proposed Retaining Wall Design. The permeable pavers near the west perimeter of the
residence should be underlain with a 12-inch layer of crushed rock or other drainage aggregate.
LIMITATIONS
The findings and recommendations stated herein are based on field observations, our experience
on similar projects and our professional judgment. The recommendations presented herein are
our professional opinions derived in a manner consistent with the level of care and skill
ordinarily exercised by other members of the profession currently practicing under similar
conditions in this area and within the project schedule and budget constraints. No warranty is
expressed or implied. In the event that site conditions are found to differ from those described in
this report, we should be notified so that the relevant recommendations in this report can be
reevaluated and modified if appropriate.
GEO Group Northwest, Inc.
April 20, 2021
8732 2091h Place SW Edmonds, Washington
CLOSING
G-5412
Page 10
We appreciate the opportunity to provide you with geotechnical engineering services for this
project. Please do not hesitate to contact us if you have any questions regarding this report.
Sincerely,
GEO Group Northwest, Inc.
95 -
Bryce Frisher, E.I.T.
Staff Geotechnical Engineer
Plates and Attachments:
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orP.�� William Chang, P.E.
NA1. Principal Engineer
Plate 1 — Site Location Map
Plate 2 —Site Plan
Plate 3 —Proposed Retaining Wall Design
Plate 4 — Hazard Areas Mapping
Attachment 1 — Boring Logs
GEO Group Northwest, Inc.
PROJECT SITE
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Source: Snohomish County SCOPI Maps
SITE LOCATION MAP
Group Northwest, Inc. PROPOSED BLOCK RETAINING WALL
- Geotechnical Engineers, Geologists, & 8732 209TH PLACE SW
Environmental Scientists EDMONDS, WASHINGTON
SCALE: NO SCALE DATE: 4/14/2021 MADE: BF CHKD: WC JOB NO: G-5412 PLATE 1
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�� PROPOSED BLOCK RETAINING WALL
�� Geotechnical Engineers, Geologists, & 8732 209TH PLACE SW
V'Al F- TM FF-F'' Environmental Scientists EDMONDS, WASHINGTON
Source: Boundary and Topographic Survey, Allied Land Surveying, Inc., 11/4/2020 SCALE AS SHOWN I DRAWN BY BF CHECKED BY WC DATE 4/13/2021 PROJECT NO. G-5412 I PLATE 3
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Source: City of Edmonds GIS
Group
Northwest, Inc.
CRITICAL AREAS MAPPING
PROPOSED BLOCK RETAINING WALL
— Geotechnical Engineers, Geologists, &
Environmental Scientists
8732 209TH PLACE SW
EDMONDS, WASHINGTON
SCALE: AS SHOWN
DATE: 4/14/2021
MADE: BF
CHKD: WC
JOB NO: G-5412
PLATE 4
SOIL CLASSIFICATION & PENETRATION TEST DATA EXPLANATION
MAJOR DIVISION
CLEAN
GRAVELS
GRAVELS
(little or no
COARSE-
(More Than Half
fines)
GRAINED SOILS
Coarse Fraction is
Larger Than No. 4
Sieve)
DIRTY
GRAVELS
(with some
fines)
SANDS
CLEAN
SANDS
(More Than Half
More Than Half
Coarse Fraction is
(little or no
by Weight Larger
Smaller Than No.
fines)
Than No. 200
4 Sieve)
Sieve
DIRTY
SANDS
(with some
fines)
SILTS
Liquid Limit
(Below A -Line on
< 50 %
Plasticity Chart,
Liquid Limit
FINE-GRAINED
Negligible
SOILS
Organics)
>50%
CLAYS
Liquid Limit
(Above A -Line on
< 50 %
Plasticity Chart,
Liquid Limit
Negligible
Organics)
>50%
Less Than Half by
Weight Larger
Liquid Limit
Than No. 200
ORGANIC SILTS
<50%
Sieve
& CLAYS
(Below A -Line on
Plasticity Chart)
Liquid Limit
> 50 %
HIGHLY ORGANIC SOILS
UNIFIED
SOIL CLASSIFICATION SYSTEM (USCS)
GROUP
TYPICAL DESCRIPTION
LABORATORY CLASSIFICATION CRITERIA
SYMBOL
WELL GRADED GRAVELS, GRAVEL -SAND
Cu = (D60 / D10) greater than 4
GW
MIXTURE, LITTLE OR NO FINES
CONTENT
Cc = (D30)2 / (1310 " D60) between 1 and 3
OF FINES BELOW
POORLY GRADED GRAVELS, AND GRAVEL -SAND
5 %
CLEAN GRAVELS NOT MEETING ABOVE
GP
MIXTURES LITTLE OR NO FINES
REQUIREMENTS
GM
SILTY GRAVELS, GRAVEL -SAND -SILT MIXTURES
GM: ATTERBERG LIMITS BELOW "A" LINE.
CONTENT
or P.I. LESS THAN 4
OF FINES EXCEEDS
CLAYEY GRAVELS, GRAVEL -SAND -CLAY
12 %
GC: ATTERBERG LIMITS ABOVE "A" LINE.
GC
MIXTURES
or P.I. MORE THAN 7
WELL GRADED SANDS, GRAVELLY SANDS,
Cu = (D60 / D10) greater than 6
SW
LITTLE OR NO FINES
CONTENT
Cc = (D30)2 / (1310 " D60) between 1 and 3
OF FINES BELOW
POORLY GRADED SANDS, GRAVELLY SANDS,
5 %
CLEAN SANDS NOT MEETING ABOVE
SP
LITTLE OR NO FINES
REQUIREMENTS
SM
SILTY SANDS, SAND -SILT MIXTURES
ATTERBERG LIMITS BELOW "A" LINE
with P.I. LESS THAN 4
CONTENT OF FINES
EXCEEDS12%
SC
CLAYEY SANDS, SAND -CLAY MIXTURES
ATTERBERG LIMITS ABOVE "A" LINE
with P.I. MORE THAN 7
ML
MH
CL
CH
OL
OH
Pt
SOIL PARTICLE SIZE
U.S. STANDARD SIEVE
FRACTION
Passing
Retained
ze
Sieve
Sieve
(MM)
(mm)
SILT / CLAY
#200
0.075
SAND
FINE
#40
0.425
#200
0.075
MEDIUM
#10
2.00
#40
0.425
COARSE
#4
4.75
#10
2.00
GRAVEL
FINE
0.75"
19
#4
4.75
COARSE
3"
76
0.75"
19
COBBLES
76 mm to 203 mm
BOULDERS
> 203 mm
ROCK
> 76 mm
FRAGMENTS
ROCK
>0.76 cubic meter in volume
INORGANIC SILTS, ROCK FLOUR, SANDY SILTS 60 -
OF SLIGHT PLASTICITY
INORGANIC SILTS, MICACEOUS OR 50
DIATOMACEOUS, FINE SANDY OR SILTY SOIL
INORGANIC CLAYS OF LOW PLASTICITY,
X 40 -
GRAVELLY, SANDY, OR SILTY CLAYS, CLEAN W
CLAYS Z
} 30 -
INORGANIC CLAYS OF HIGH PLASTICITY, FAT F
CLAYS U
20
ORGANIC SILTS AND ORGANIC SILTY CLAYS OF Q
LOW PLASTICITY d
10
7�
ORGANIC CLAYS OF HIGH PLASTICITY 4�
MMMON Ron
.1 .... I'll..
0 10 20 30 40 50 60 70 80 90 100
PEAT AND OTHER HIGHLY ORGANIC SOILS I LIQUID LIMIT (%)
GENERAL GUIDANCE FOR ENGINEERING PROPERTIES OF SOILS, BASED ON STANDARD
PENETRATION TEST (SPT) DATA
SANDY SOILS
.1 .... I'll..
0 10 20 30 40 50 60 70 80 90 100
PEAT AND OTHER HIGHLY ORGANIC SOILS I LIQUID LIMIT (%)
GENERAL GUIDANCE FOR ENGINEERING PROPERTIES OF SOILS, BASED ON STANDARD
PENETRATION TEST (SPT) DATA
SANDY SOILS
SILTY & CLAYEY SOILS
Unconfined
Blow Counts
Relative
Friction Angle
Blow Counts
Description
Strength Clu,
Description
N
Density, %
AI, degrees
N
tsf
0-4
0 -15
Very Loose
< 2
< 0.25
Very soft
4-10
15 - 35
26 - 30
Loose
2-4
0.25 - 0.50
Soft
10-30
35 - 65
28 - 35
Medium Dense
4-8
0.50 - 1.00
Medium Stiff
30-50
65 - 85
35 - 42
Dense
8 - 15
1.00 - 2.00
Stiff
> 50
85 - 100
38 - 46
Very Dense
15 - 30
2.00 - 4.00
Very Stiff
> 30
> 4.00
Hard
Group Northwest, Inc.
Geo technical Engineers, Geologists, &
Environmental Scientists
13240 NE 20th Street, Suite 10 Bellevue, WA 98005
Phone (425) 649-8757 Fax (425) 649-8758 TAT ATE A 1
BORING NO. HA-1 Page 1 of 2
Completed By: BF Date Drilled: 3/29/2021 Surface Elev. 402'
Depth
ft.
0
'?
W
USCS
Code
Description
Sample
4
Probing
Rod Penet.
(in.)
Water
Content
off"
Other Tests/
Comments
Loc.
No.
SP - SM
SAND with SILT, fine-grained, loose, brown, moist, topsoil
4"
material.
18"
SM
SILTY SAND, brown, moist, fine-grained, loose, some thin
roots, rare GRAVEL.
1
SM
As above.
15"
2
SM
SILTY SAND, brown, fine-grained with some coarse -grained
10"
SAND, moist, some GRAVEL, loose.
3
SP
SAND, brown, loose, fine-grained, some thin roots, rare
6"
GRAVEL, moist.
4
SP - GP
SAND with GRAVEL, brown, moist, fine-grained, medium,
3"
dense, some silty fines.
SP - GP
SAND and GRAVEL, grayish light brown, medium dense,-
1"
g
1
fine-grained, damp to moist.
LEGEND: I 2" O.D. SPT Sampler p Water Level noted during drilling
T 3" O.D. California Sampler Water Level measured at later time, as noted
BORING LOG
Group Northwest, Inc.
PROPOSED BLOCK RETAINING WALL
- Geotechnical Engineers, Geologists, a
8732 209TH PLACE SW
Environmental Scientists
EDMONDS, WASHINGTON
JOB NO. G-5412
I DATE 4/6/2021
PLATE A2
BORING NO. HA-1 Page 2 of 2
Completed By: BF Date Drilled: 3/29/2021 Surface Elev. 402'
Depth
0
USCS
Description
Sample
4
Probing
Rod Penet.
Water
Content
Other Tests/
ft.
°?
W
Code
(in.)
off"
Comments
Loc.
No.
Depth of boring: 5 feet. Refusal.
Drilling Method: Hand Auger
Sampling Method: Grab and hand tools.
Groundwater not encountered.
6
7
8
9
10
LEGEND: I 2" O.D. SPT Sampler p Water Level noted during drilling
T 3" O.D. California Sampler Water Level measured at later time, as noted
BORING LOG
Group Northwest, Inc.
PROPOSED BLOCK RETAINING WALL
- Geotechnical Engineers, Geologists, a
8732 209TH PLACE SW
Environmental Scientists
EDMONDS, WASHINGTON
JOB NO. G-5412
I DATE 4/6/2021
PLATE A3
BORING NO. HA-2 Page 1 of 1
Completed By: BF Date Drilled: 3/29/2021 Surface Elev. 398'
Depth
0
USCS
Description
Sample
4
Probing
Rod Penet.
Water
Content
Other Tests/
ft.
'?
W
Code
(in.)
off"
Comments
Loc.
No.
SP
SAND, fine-grained, brown to grayish brown, loose, moist.
8"
SP
SAND, fine-grained, loose, grayish brown, moist, some
6"
GRAVEL.
3"
SP - SM
SAND with SILT, grayish brown to light brown, fine-grained,
some GRAVEL, moist, medium dense.
1
1"
SP
SAND, medium dense, fine-grained, grayish brown,
some GRAVEL, moist.
2
SP
SAND, medium dense to dense, fine-grained, grayish brown,
< 1"
rare GRAVEL, moist.
Depth of boring: 2 feet. Refusal.
Drilling Method: Hand Auger
Sampling Method: Grab and hand tools.
Groundwater not encountered.
3
4
5
LEGEND: I 2" O.D. SPT Sampler p Water Level noted during drilling
T 3" O.D. California Sampler Water Level measured at later time, as noted
BORING LOG
Group Northwest, Inc.
PROPOSED BLOCK RETAINING WALL
- Geotechnical Engineers, Geologists, a
8732 209TH PLACE SW
Environmental Scientists
EDMONDS, WASHINGTON
JOB NO. G-5412
I DATE 4/6/2021
PLATE A4