RESUB 1-Geotechnical_Report+7.23.2022_GEOTECHNICAL REPORT
PAWLING RESIDENCE
EDMONDS, WASHINGTON
MAY 17, 2013
BY:
SCOTT M. PAWLING, PE, MSCE
TABLE OF CONTENTS
Page
1.0
INTRODUCTION......................................................................................................................1
2.0
WALL DESCRIPTIONS..............................................................................................................1
3.0
SUBSURFACE CONDITIONS.....................................................................................................2
4.0
MECHANICALLY STABILIZED EARTH (MSE) WALL DESIGN.....................................................3
4.1 Seismicity....................................................................................................................3
4.2 External and Internal Wall Stability............................................................................4
4.3 Global Stability...........................................................................................................5
4.4 Backfill Gradation, Placement and Compaction........................................................6
4.5 Total and Differential Settlement..............................................................................7
5.0
LIMITATIONS...........................................................................................................................7
6.0
REFERENCES...........................................................................................................................8
TABLES
1 Interpreted Soil Properties..................................................................................... 3
2 Mechanically Stabilized Earth Wall Design Details ................................................. 5
FIGURES
1 Site and Exploration Plan
2 Mechanically Stabilized Earth (MSE) Wall Detail
3 Typical MSE Wall Subdrainage and Backfill
APPENDIX
A Subsurface Exploration Logs [Figures A-1 and A-2]
i
GEOTECHNICAL REPORT
PROPOSED MSE WALLS AND GRADING
PAWLING RESIDENCE
EDMONDS, WASHINGTON
1.0 INTRODUCTION
This report provides the details and results of geotechnical analyses for proposed mechanically
stabilized earth (MSE) walls in the backyard of the Pawling Residence, located at 755 Daley
Street in Edmonds, Washington. Details and recommendations for construction of the MSE
walls are presented herein. The maximum design wall height is 6.0 feet including 1.0 feet of
embedment below final grade (maximum 5.0 feet exposed wall height). The total length of
proposed MSE walls is approximately 70 feet with three 90-degree outside corners, two 90-
degree inside corners, and a staircase descending atop one wall section.
The existing grade in the backyard of the Pawling residence slopes gently downward from west
to east, as shown in the Site and Exploration Plan (Figure 1). Proposed walls will retain fill to
raise the grade and level the upper (western) portion of the yard to approximate Elevation 102
feet. Some excavation will be necessary to lower the existing grade to approximate Elevation
97 feet to level the lower (eastern) yard. The facing for proposed walls will consist of
RisiStone° RomanPisa° and RisiStone Pisa28 modular blocks, as specified by Studio 342
Landscape Architecture of Edmonds, Washington.
2.0 WALL DESCRIPTIONS
The layout of proposed MSE and gravity retaining walls is presented in Figure 1. The MSE walls
generally divide the upper and lower yards and include exposed wall heights between 2.5 and
5.0 feet. The wall layout generally follows existing site topography in order to maintain a
maximum exposed wall height of 5.0 feet, and this is accomplished with five 90-degree
inside/outside wall bends over a distance of about 25 feet. One MSE wall located adjacent to
the residence and deck will intersect the eastern deck foundations. According to as -built
records for the deck, the deck eastern footings are founded at approximate Elevation 96 feet.
Construction of the MSE wall at this location should be feasible; i.e., construction should not
involve soil disturbance below Elevation 96 feet at the footing locations. Other deck
foundations are closer to the existing ground surface and should not be impacted by
construction if overexcavation is performed carefully by an experienced contractor.
The proposed retaining wall that runs parallel with the northern property boundary has a
design height of 3.0 feet and less (2.0 feet and less exposed) and will be constructed as a gravity
wall. The proposed gravity wall does not require permitting through the City of Edmonds;
therefore, this wall is not discussed in detail in this geotechnical report. Construction of the
gravity wall should proceed in accordance with the manufacturer's recommendations based on
the subsurface conditions at the site as described in this report.
3.0 SUBSURFACE CONDITIONS
Two hand borings were performed along the proposed MSE wall alignment in order to classify
soils and interpret subsurface conditions at the site. Approximate locations of the hand
borings, B-1 and B-2, are shown in Figure 1. Each boring was performed by a licensed
geotechnical engineer using a manually operated auger and was extended to a depth of 10.3
feet. Soil samples were collected at maximum 2-foot intervals and classified in accordance with
the Unified Soil and Classification System (USCS). Relative densities of subsurface soils were
estimated based on the advancement rate of the auger. No groundwater was encountered
during drilling.
Detailed logs of the borings are included in Appendix A. Based on the results of the borings, the
generalized subsurface conditions may be described as follows:
• From about 0.0 to 0.5 feet below ground surface (bgs): Topsoil
• From about 0.5 to 5.5 feet bgs: Medium dense, brown, slightly silty, gravelly SAND;
moist; subrounded gravel; SP-SM
• From about 5.5 to 10.3 feet bgs: Medium dense to dense, light brown, gravelly SAND;
moist; subrounded gravel; occasional layers of dense, sandy gravel; SP
The geologic map for the Edmonds area (Minard, 1983) identifies near -surface soils at the
Pawling residence as glacial and nonglacial transitional beds (Qtb). According to Minard, Qtb
soils are generally fine-grained or fine sand but grade upward into the overlying glacial advance
outwash deposit (Qva) at some localities. Overlying Qva soils are generally sands and gravels
with variable amounts of silt. Soils encountered at the Pawling residence appear to be within
the upper sequence of the Qtb deposit where coarse -grained soils are predominant. Steep
slopes located near the site appear to be comprised of Qva. A distance of about 150 feet from
the site to the closest Qva slope is reasonable for site soils to be considered within the upper
Qtb sequence grading to Qva.
2
Table 1 (below) presents the interpreted soil properties for wall design and stability analyses.
Soil properties shown in Table 1 assume that on -site soils would be reused for backfill in the
reinforced zone of MSE walls; select backfill would not be imported.
TABLE 1
INTERPRETED SOIL PROPERTIES
Unit
Weight
Friction Angle
Z
Cohesion (lb/ft )
Material
(lb/ft3)
(degrees)
Reinforced Zone
Backfill
125
34
-
Retained Soil
120
32
-
Foundation Soil
125
36
-
Note: See Section 4.3.
4.0 MECHANICALLY STABILIZED EARTH (MSE) WALL DESIGN
The MSE wall design was completed based on allowable -stress -design methods presented in
the Federal Highway Administration (FHWA) manual for design and construction of MSE walls
(Elias et al., 2001), the National Concrete and Masonry Associate (NCMA) design manual for
segmental retaining walls (NCMA, 2009), and 2012 International Building Code (International
Code Council [ICC], 2011).
4.1 Seismicity
According to the 2012 International Building Code (ICC, 2011), seismic hazards for walls are
evaluated on the basis of a Maximum Credible Earthquake (MCE) with a 2 percent probability of
exceedance in 50 years, or 2,475-year return period. Based on regional probabilistic ground
motion hazard studies by the U.S. Geological Survey (USGS, 2008), the peak horizontal ground
acceleration (PGA) for the 2,475-year event at the project site is 0.48g for a Site Class B.
Based on interpreted soil properties in Table 1 and site geology, the site is best classified as Site
Class D. A site soil response factor (FPGA) is applied to the PGA to account for differences in Site
Class. This factor depends on the PGA value and Site Class. Using AASHTO design standards,
the site factor FPGA is 1.02 (AASHTO, 2010). As such, for Site Class D, the PGA is 0.49g. A seismic
coefficient equal to about one-half of the site -specific PGA, or 0.25, was used for seismic
design.
4.2 External and Internal Wall Stability
MSE wall design analyses were performed considering the internal and external stability of the
wall system for static, seismic, and temporary (construction) conditions. We estimated factors
of safety (FS) for the various conditions and failure modes. Geogrid tensile strength, pullout
resistance, and direct sliding were considered for internal stability calculations. External
stability was estimated for bearing capacity, base sliding, overturning, and global failure modes.
Finally, total and differential elastic settlements were estimated.
The MSE wall design was completed using the computer program MSEW°, Version 3.0 from
ADAMA Engineering, Inc (ADAMA, 2010). External and internal wall stability was evaluated
assuming an extensible polyester geogrid connected to specified Vx8"x12" modular blocks.
The maximum wall height considered for design was 6.0 feet, which consists of 5.0 feet of
exposed face and 1.0 feet of embedment. Passive resistance at the toe of a wall was ignored
for external stability analyses. Wall design details are provided in Table 2 and Figure 2.
While groundwater was assumed to be deep, we recommend standard MSE wall drainage as
shown in Figure 3. The subdrain pipe in Figure 3 should discharge to a suitable infiltration
location or catch basin on the site.
M
TABLE 2
MECHANICALLY STABILIZED EARTH (MSE) WALL DESIGN DETAILS
Component
Description/Value
Commentary
Biaxial geogrid: equal strength in length
Reinforcement Material
Mirafi° Miragrid® 2XT
and width dimensions should be taken
advantage of when constructing 90-
degree outside corners
Reinforcement Length
Varies per wall height
See Figure 2
and geogrid layer depth
RisiStone®
Modular blocks dimensioned
Facing Material
RomanPisa® and Pisa2®
6"x8"x12"; RomaPisa where exposed,
Pisa2 where below final grade
Embedment
Min. 1.0 feet
6 inches of compacted
Contractor should attempt to limit
Leveling Pad
crushed rock
leveling pad dimensions to those shown
in Figure 2
Coincides with pre -manufactured
Batter
1H:8V
notches in modular blocks
Pedestrian traffic only; no storage, no
Live Load
50 psf
construction equipment behind wall
except hand -operated compaction
equipment
Maximum Exposed Wall Height
5.0 feet
Groundwater
-
Case of GW at bottom of wall checked
in analyses
Smaller than typ. vertical spacing is
Reinforcement Vertical Spacing
Max. 1.0 feet
function of reusing on -site soils for
backfill in reinforced zone
Distance Below TOW to
Min. 2.0 feet to
Irrigation lines planned for upper 2 feet
Top Reinforcement Layer
Max. 2.5 feet
Notes:
H:V = horizontal to vertical
Max. = maximum
Min. = minimum
psf = pounds per square foot
TOW = top of wall
typ. = typical
4.3 Global Stability
Global stability of the native soil was conducted with traditional limit equilibrium stability
techniques using version 7.16 of the commercial software Slope/W developed by Geo-Slope
International (2007). For our analysis, we considered the Morgenstern -Price method -of -slices
to calculate the factor of safety for each trial slip surface, as this method provides both force
and moment equilibrium. Static and seismic loading conditions were evaluated in our analysis.
For the seismic loading condition, a horizontal acceleration coefficient of 0.25g was used, which
was about one-half of the PGA.
5
As indicated in Table 1, the assumed friction angle for the foundation soil (native soil) was
36 degrees. The assumed friction angle for backfill in the unreinforced zone and native soils
above the foundation was 32 degrees. Our analyses indicated static and seismic factors of
safety greater than 1.5 and 1.1, respectively. These factors of safety are above the minimum
factors of safety for design recommended by Elias et al. (2001) and the IBC.
4.4 Backfill Gradation, Placement and Compaction
We recommend that all backfill material used for walls be free draining and free from organic
and other deleterious material. The material should also be substantially free of shale or other
soft, poor -durability particles, and should not contain recycled materials such as glass, shredded
tires, portland cement concrete rubble, or asphaltic concrete rubble. Sand and gravel suitable
for reuse (less than approximately 7% fines [particles passing the No. 200 sieve]) should be
stockpiled on site during excavation activities. Otherwise, sand and gravel that is imported
should be manufactured from crushed rock. Prior to the placement of MSE wall backfill, any
ponding water should be drained from the area and the subgrade should be compacted to a
dense, unyielding condition, if necessary.
The Washington State Department of Transportation (WSDOT) 2006 Standard Specifications for
Road, Bridge, and Municipal Construction provide gradation criteria for several backfill
materials. Backfill in the reinforced zone of an MSE wall should generally consist of gravel
borrow as specified in WSDOT Section 9-03.14(1), except the maximum particle size should be 3
inches. Based on soils classifications performed on samples retrieved from the hand borings, in
general, on -site soils to be excavated would not meet the WSDOT gradation requirements for
MSE wall backfill. However, in my opinion, the majority of on -site soils are free -draining and
suitable for use as MSE wall backfill if the material is well compacted, gravels larger than 3
inches in diameter are removed, vertical spacing between geogrid layers is maximum 12 inches,
and a drainage system is installed as shown in Figure 3. As noted in Figure 2, reuse of onsite
soils as backfill for MSE walls is contingent on approval from the Engineer of Record based on a
visual inspection of stockpiled materials in the field.
All backfill should be placed in layers not exceeding 4 inches loose thickness and compacted
with hand -operated compactors to at least 95 percent of the Modified Proctor maximum dry
density (ASTM D 1557). A minimum of four lifts shall be compacted between two adjacent
geogrid layers; i.e., a minimum of four lifts per 12 inches of elevation gain.
R
4.5 Total and Differential Settlement
The estimated settlement of the walls can be attributed to two distinct sources: settlement of
the subsurface materials subjected to the new load and settlement of the wall backfill material.
These settlements will occur during construction and may continue after the wall is built. Based
on the hand borings and my experience with similar soils, we estimate that post -construction
settlement of subsurface soils will be % inch to negligible. Settlement of backfill material
should be less than % inch provided the fill is properly placed and compacted. This settlement
is anticipated to occur within the first year following construction. Differential settlements
should also be acceptable and within the tolerable limits recommended by RisiStone, the
manufacturer of the specified modular blocks.
5.0 LIMITATIONS
This report was prepared for the exclusive use of Studio 342 Landscape Architecture and Scott
M. Pawling. The analyses, conclusions, and recommendations contained in this report are
based on site conditions encountered at the time of the site visit only. The assumptions
provided in this report and used as the basis of this design should be confirmed prior to
construction or included in the construction contract. If subsurface conditions different from
those described in this report are observed or appear to be present beneath excavations, we
should be advised at once so that we can review these conditions and reconsider our design
where necessary.
Within the limitations of the scope, schedule and budget, the analyses, conclusions and
recommendations presented in this report were prepared in accordance with generally
accepted professional geotechnical engineering principles and practice in this area at the time
we prepared our report. We make no other warranty, either express or implied. These
conclusions and recommendations were based on our understanding of the project as
described in this report and the site conditions specified in the statement of work.
�GJAAEL
� n
,p R 45873 9 ��
7
Scott M. Pawling, P.E.
Geotechnical (Civil) Engineer
License No. 45873
6.0 REFERENCES
ADAMA Engineering, 2010, Mechanically Stabilized Earth Walls: Program MSEW 3.0, Copyright
1998-2010, ADAMA Engineering.
ASTM International (ASTM), 2012, Annual book of standards, Construction, v. 4.08, Soil and
rock (1): D 420 — D 4914: West Conshohocken, Pa.
Elias, V., Christopher, B.R., and Berg, R.R., 2001, Mechanically stabilized earth walls and
reinforced soil slopes design and construction guidelines, Federal Highway Administration
(FHWA) and National Highway Institute (NHI) manual no. FHWA-NHI-00-043.
Geo-Slope International, 2007, Slope/W (Geostudio 2007), version 7.16, Calgary, Alberta,
Canada.
International Code Council, Inc., 2011, International building code 2012, Country Club Hills,
Illinois.
Minard, J.P., 1983, Geologic map of the Edmonds East and part of the Edmonds West
quadrangles, Washington, U.S. Geological Survey (USGS) map MF-1541.
U.S. Geological Survey (USGS), 2008, Interactive Deaggregations, accessed August 3, 2010, from
USGS website: http://eqint.cr.usgs.gov/deaggint/2008/index.php
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Plsa2 block retaining wall
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Leyland Cypress
screen hedge
6'-0' height cedar fence x
Roman Pisa block
and cap stairs
Roman Pisa block
retaining wall H/1�,
TW 102.0
transition to 36" height
cedar fence
24" x 24" architectural slab /
pavers with lawn joints (typ.)
6-0" height cedar fence
Pisa2 block retaining wall „
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TW 102.0
TW 103.0
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9" , x w- "
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24" x 24" sand -set architectural
concrete slab paver patio
cedar arbor structure
LEGEND
• B-1 Boring Designation and
Approximate Location
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planter planter _
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asphalt I
parking area I
F777777— — — — — _ T (95.80)
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black powder coated
tubular steel mail box
frame with new black
mailboxes
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Site and
Exploration
Plan -
NOT TO SCALE f— —
FIG. 1
NORTH
RisiStone® Coping Unit or
Revers -a -Cap Coping Unit
Exposed Modular Blocks:
RisiStone® RomanPisa®
Buried Modular Blocks: 1
RisiStone® Pisa2®
H 8
Finish Grade
(Elev. 97.0' Typ.)
12" Min. Embedment
--_I6
Crushed Rock Leveling Pad
Geogrid Schedule
Finish Grade
(Elev. Varies)
Min. 24" to Max. 30" I
Miragrid® 2XT
Geogrid
L2 (See Geogrid Schedule)
L1 (See Geogrid Schedule)
Reinforced Zone Unreinforced Zone
Approved
Max. 12" On -Site Soils
6" Typ.
din.
Not to Scale
H
L1
L2
Type
(Ft)
(Ft)
(Ft)
5.5 - 6.0
5.0
7.0
Mirafi®
4.5 - 5.0
4.0
6.0
Miragrid®
2XT
3.5 - 4.0
4.0
5.0
LEGEND
H = Design Wall Height
L1 = Lower Geogrid Layers
L2 = Top Geogrid Layer
NOTES
1. L1 and L2 include portion of geogrid between
modular blocks.
2. Only hand -operated compaction equipment
shall be used behind the wall, up to a
horizontal distance equal to H.
3. See Figure 3 for additional details.
DATE: MAY2013 rlVuKt
SCALE: NOT TO SCALE PAWLING RESIDENCE MECHANICALLY STABILIZED EARTH (MSE) ^
DRAWN BY: C.TAYLOR EDMONDS, WASHINGTON WALL DETAIL L
REVISED
Facing Finish Grade Drainage Sand and Gravel
(Elev. Varies) (See Note 2)
Wall Batter
(as per design) 18" Min. Ilk�
Geosynthetic or Reinforced Retained Soil
Steel Reinforcement Fill Zone
On -Site Soils
(See Note 1)
Finish Grade
(Elev. 97.0' Typ.)
12" Min.
2"Min.
ax.
Not to Scale
NOTES
1. On -site soils used for backfill shall be free of organic
matter and debris, and shall be approved in the field for
reuse by the Engineer of Record.
2. Drainage sand and gravel shall meet the requirement of
Section 9-03.13 of the WSDOT standard specifications.
Sand and gravel should be manufactured from crushed
rock. Alternatively, on -site soils excavated from below
approx. Elev. 96 feet may be used as drainage sand if
approved in the field by the Engineer of Record.
3. The subdrain should consist of 4-inch-diameter
(minimum), slotted or perforated plastic pipe meeting
the requirements of AASHTO M 252; 1/8-inch maximum
slot width; 3/16- to 3/8-inch perforated pipe holes in the
lower half of pipe, with lower third segment unperforated
for water flow; tight joints; sloped at a minimum of
6"/100' to drain; cleanouts to be provided at regular
intervals.
4. Cover subdrain pipe with 8 inches (minimum) of washed
pea gravel. Washed pea gravel to be graded from
3/8-inch to No. 8 standard sieve.
DATE: MAY 2013
SCALE: NOT TO SCALE PAWLING RESIDENCE
DRAWRSY: C.TAYLOR EDMONDS, WASHINGTON
Terrace Excavation Slope
(Ref. 2-03.3(14) WSDOT Standard
Specifications); Excavation Slope is
Contractor's Responsibility; For Fill
Walls not Terraced into Existing
Ground, Drain May Be Vertical
8" Min. Cover of Pea Gravel
(6" Min. on Sides of Pipe; 2" Below)
Drainage Geotextile (See Note 5)
Pea Gravel (See Note 4)
Subdrain Pipe (See Note 3)
5. Drainage geotextile to be placed below subdrain pipe
pea gravel only. Geotextile should not be placed
below retaining wall, between drainage sand and
gravel and retained soil, or wrapped over the top of
the pea gravel. Drainage geotextile shall meet the
requirements of WSDOT Standard Specification
Section 9-33.2, for a non -woven, low survivability
Class B geosynthetic.
6. Drainage sand and gravel, pea gravel, and on -site
soils should be placed in layers not exceeding 4
inches loose thickness and compacted to at least 95
percent of its Modified Proctor maximum dry density
(ASTM D 1557).
7. Design of wall system is shown in Figure 2.
TYPICAL MSE WALL
SUBDRAINAGE AND BACKFILL
FIGURE
REVISED
J.013 NO.
LOGGED BY
DRILL CONTRACTOR
DRILLER TYPE DRILL��
SIZE & TYPE OF CASING
SAMPLE DATA
TIME
SAMPLE NO.
F
0. �
uj �
FROM
DRIVING
RESISTANCE
BLOWS/61N.
LENGTH
DRILL
ACTION
CONTACTS
GROUNDWATER
PID
DATE
TYPE
To
NO. SAVED
ice` to
DEPTH
FROM I TO
(Tjc� —�—,
C25, �,K-,�
CS FIELD LOG OF BORING
JOB
BORING NO. ELEV.
LOCATION 2 dic-L 6,4N1,f
mtj 54��j qUoLu-4�, 55
DATE WEATHER -
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FIELD CLASSIFICATION
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HAMMER WT. —
HAMMER SYSTEM
ROD DIA. —
WATER LEVEL
DROP —
NO.OFTURNS
TIME I
FOOTAGE DRILLED
ATTEMPTED
NO. SAMPLES:
RECOVERED
TIME DISTRIBUTION THIS HOLE
ON HOLE DONE DRILLING
DRILLING OFF HOLE
BORING NO.=
DATE
FIELD LOG OF BORING
•: NO.
LOGGED BY SM JOB
DRILL CONTRACTOR BORING NO. ELEV.
DRILLER � �,) TYPE DRILL 1a- 4 Aur tr LOCATION L Lne w CL pogf �' I e , �,
SIZE & TYPE OF CASING DATE 1 L L y WEATHER r-4'�` 4. A'
SAMPLE DATA
TIME
SAMPLE NO.
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FROM
DRIVING
RESISTANCE
BLOWS /6 IN.
LENGTH
ILL
ACTION
CONTACTS /PID
GROUNDWATER
ICHEMICAL
SAMPLE
(Y) OR (N)
DATE
TYPE
TO
NO. SAVED
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FIELD LOG OF BORING
REMARKS
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HAMMER WT. DROP
HAMMER SYSTEM
ROD DIA. NO.OF TURNS
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WATER LEVEL
TIME
ATTEMPTED
NO. SAMPLES:
RECOVERED
TIME DISTRIBUTION THIS HOLE
ON HOLE DONE DRILLING.
DRILLING OFF HOLE—
m
DATE
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BORING NO. `� —�' �I� � � � _=