APPROVED PLN BLD2020-0479+Geotechnical_Report+5.11.2020_12.23.11_PMAges Engineering, LLC PuyalluP.O. Box 935
p, WA. 98371
(253)845-7000
www.agesengmeering.com
A Geotechnical and Environmental Services, LLC
GEOTECHNICAL REPORT
Meadowdale Road Residential
16216 N. Meadowdale Road
Edmonds, Washington
APPROVED BY PLANNING Parcel Number: 00649500001000
Sep 02 2020
Project No. A-1479-1
Prepared For:
Brett Buehler
20516 — 8011 Avenue W.
Edmonds, WA 98026
February 29, 2020
,ECEIVED
May 212020
CITY OF EDMONDS
DEVELOPMENT SERVICES
DEPARTMENT
Ages
P.O. Box 935
Engineering,
LLC
Puyallup, WA.98371
Main (253) 845-7000
A Geotechnical and Environmental Services LLC
www.agesengmeenng.com
February 29, 2020
Project No. A-1479-1
Brett Buehler
20516 — 801h Avenue W.
Edmonds, WA 98026
Subject: Geotechnical Report
Meadowdale Road Residential
16216 N. Meadowdale Road
Edmonds, Washington
Parcel Number: 00649500001000
Dear Mr. Buehler,
As requested, we have conducted a geotechnical study for the subject project. The attached
report presents our findings and recommendations for the geotechnical aspects of project design
and construction.
Our field exploration indicates the site is generally underlain with native sand with silt and trace
amounts of gravel consistent with Advance Outwash. We did not encounter groundwater seepage
in any of the test holes advanced on the site.
In our opinion, the soil and groundwater conditions at the site are suitable for the planned
development. The new retaining wall can be supported on the existing organic -free native soils
observed immediately below the ground surface, or on structural fill placed above these native
soils.
Detailed recommendations addressing these issues and other geotechnical design considerations
are presented in the attached report. We trust the information presented is sufficient for your
current needs. If you have any questions or require additional information, please call.
Respectfully Submitted,
Ages Engineering, W
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Bernard P. Knoll, I1 �s FGISTE" C?�
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TABLE OF CONTENTS
1.0 PROJECT DESCRIPTION...................................................................I
2.0 SCOPE.......................................................................................... I
3.0 SITE CONDITIONS..........................................................................2
3.1 Surface.................................................................................2
3.2 Soils....................................................................................2
3.3 Mapped Soils.........................................................................3
3.4 Groundwater..........................................................................3
4.0 GEOLOGIC HAZARDS.....................................................................4
4.1 General..................................................................................4
4.2 Landslide................................................................................4
4.3 Seismic.................................................................................5
4.4 Erosion..................................................................................6
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5.1 General..................................................................................7
5.2 Slope Stability Analysis.............................................................7
5.3 Development in Potential Landslide Hazard Areas...............................9
5.4 Site Preparation and Grading.......................................................12
5.5 Excavations...........................................................................14
5.6 ComerStone® Retaining Wall....................................................15
5.7 Permanent Slopes and Embankments.............................................16
6.0 ADDITIONAL SERVICES...................................................................17
7.0 LIMITATIONS..................................................................................1 7
Figures
Site Vicinity Map...............................................................................Figure 1
Exploration Location Plan.....................................................................Figure 2
GeologicMap..................................................................................Figure 3
Pre- and post -Construction Slope Stability Section ......................................Figure 4
Post -Construction Seismic Slope Stability Section .......................................Figure 5
Appendix
Site Exploration..........................................................................Appendix A
CornerStone® Wall Calculations ......................................................Appendix B
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Geotechnical Report
Meadowdale Road Residential
16216 N. Meadowdale Road
Edmonds, Washington
1.0 PROJECT DESCRIPTION
The project will consist of a residential development. We discussed the planned development
with the project contractor and were provided with two document s from the City of Edmonds.
We were provided with a City of Edmonds Building Division Plan Review Comments Letter
dated October 15, 2019 and a City of Edmonds Planning Division Plan Review Comments Letter
dated October 14, 2019. Based on these discussions and our review of the documents provided to
us, we understand the existing railroad tie retaining wall on the site is being replaced with the
CornerStone® Retaining Wall System. We understand the Cornerstone® F-100 blocks will be
used. The wall will be approximately 120 feet long and have a maximum total height of 4.0 feet.
The new wall will extend along the western side of the existing driveway and terminate at the end
of the existing concrete retaining wall located adjacent the southwest corner of the existing
residence on the site. Access to the site is provided by N. Meadowdale Road located along the
northeast side of the site.
The conclusions and recommendations presented in this report are based on our understanding of
the above stated site and the planned project design features. If actual site conditions differ, the
planned project design features are different than we expect, or if changes are made, we should
review them in order to modify or supplement our conclusions and recommendations as
necessary.
2.0 SCOPE
On February 22, 2019 we advanced two hand -augured test holes to a maximum depth of 10.0 feet
below surface grades and 3.0 feet below the bottom of the planned retaining wall location. Using
the information obtained from our subsurface exploration, we developed geotechnical design and
construction recommendations for the project. Specifically, this Preliminary Geotechnical Report
addresses the following:
• Reviewing the available geologic, hydrogeologic and geotechnical data for the site area,
and conducting a geologic reconnaissance of the site area.
• Addressing the appropriate geotechnical regulatory requirements for the planned site
development, including a Geologic Hazard evaluation.
• Advancing two hand augured test holes in the planned new development area to a
maximum depth of approximately 10.0 feet below surface grades.
• Providing geotechnical recommendations for site grading including site preparation,
subgrade preparation, fill placement criteria, suitability of on -site soils for use as
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structural fill, temporary and permanent cut and fill slopes, and drainage and erosion
control measures.
• Providing geotechnical design and construction recommendations for a new
CornerStone® Retaining Wall on the subject site.
• Providing an evaluation of the existing slopes on the site.
• Providing recommendations for site drainage.
It should be noted that our work does not include services related to environmental remediation or
design and performance issues related to moisture intrusion through walls. An appropriate design
professional or qualified contractor should be contacted to address these issues. Our work does
not include infiltration testing.
3.0 SITE CONDITIONS
3.1 Surface
The subject site is an irregular -shaped residential parcel located at 16216 North Meadowdale
Road in the Meadowdale area of Edmonds, Washington. The site is currently occupied with a
single-family residence located in the approximate center of the site. A driveway extends from
North Meadowdale Road to the south side of the existing residence. The site is bordered with
existing single-family residential parcels to the north, west, and south, and North Meadowdale
Road to the east. The location of the site is shown on the Site Vicinity Map provided in Figure 1.
A CornerStone® retaining wall is currently under construction along the western (uphill) side
of the driveway on the site. Wall construction began at the south end of the planned wall
alignment and was stopped after approximately 30 feet of the wall was constructed. The
remaining portions of the planned wall alignment have been exposed and are awaiting the
continued construction of the new CornerStone® wall. We understand a wooden retaining wall
previously occupied the same alignment and the new CornerStone® wall alignment. The
previously existing wooden wall has been removed. Several pallets of CornerStone® F-100
blocks are stockpiled on the site.
Surface grades in the vicinity of the site slope down to the east. Surface grades on the site slope
down to the east at inclinations ranging from 10 to 50 percent. The steeper grades are located
along the western (uphill) side of the site.
Site vegetation consists of various medium-sized evergreen and deciduous trees with moderately
thick underbrush. The current site conditions are shown on the Exploration Location Plan
provided in Figure 2.
3.2 Soils
The soils we observed at the site generally consist of sand with silt and varying amounts of gravel
consistent with Advance Outwash.
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In Test Hole TH-1, located at the northern end of the recently constructed ComerStone® wall
alignment, we encountered 10 inches of forest duff and topsoil overlying loose to medium dense,
moist, tan sand with silt to a depth of 4.0 feet below surface grades. These soils were exposed on
the cut slope behind the wall alignment. Excavations below the base of the wall in this location
encountered moist, medium dense, slightly cemented, tannish -gray sand with silt and gravel
consistent with Advance Outwash to a total depth of 7.0 feet below surface grades. In Test Hole
TH-2, located at the northern end of the planned wall alignment adjacent the concrete wall by the
SW building comer, we encountered 10 inches of forest duff and topsoil overlying loose to
medium dense, moist, tan sand with silt to a depth of 4.0 feet below surface grades. Below 4.0
feet, the soils became moist, medium dense, slightly cemented tannish -gray sand with silt and
trace amounts of gravel to a depth of 7.0 feet below surface grades. These soils were exposed on
the cut slope behind the wall alignment. Excavations below the base of the wall in this location
encountered moist, dense, slightly cemented, gray sand with silt and gravel consistent with
Advance Outwash to a total depth of 10.0 feet below surface grades.
Figures A-1 through A-2 present more detailed descriptions of the subsurface conditions
encountered in the test holes. The approximate test hole locations are shown on the Exploration
Location Plan provided in Figure 2.
3.3 Mapped Soils
According to The Geologic Map of the Edmonds East and Part of the Edmonds West
Quadrangles, Washington, by James P. Minard (1983), the soils in the vicinity of the site are
mapped as Advance Outwash (Qva). The Advance Outwash was deposited in front of the
advancing glacial ice and was consequently over -ridden by the glacial ice mass. The Advance
Outwash is described as mostly clean, gray, pebbly sand with increasing amounts of gravel higher
in the section. Distinctive features of the outwash are its well -developed cross and horizontal
stratification, and cut and fill structures. Locally, some of these sediments are stained by iron
oxide precipitated from groundwater. Fine-grained sand and some silt are common in the lower
part of the unit and also locally occur sparingly in the upper part. The Advance Outwash, and all
units under the Advance Outwash, are typically in a dense to very dense condition, and will
exhibit a relatively high shear strength and low compressibility where undisturbed. The near
surface soils at the site have been disturbed by natural weathering processes that have occurred
since their deposition. No springs or groundwater seepage was observed on the surface of the site
at the time of our site visit. A copy of the Geologic Map for the subject site is provided in Figure
3.
3.4 Groundwater
We did not encounter groundwater seepage in any of the test holes advanced at the site. However,
we expect a seasonal perched water table develops on top of the underlying dense glacially
consolidated soils during the wet winter months. Groundwater levels and flow rates will fluctuate
seasonally and typically reach their highest levels during and shortly following the wet winter
months (October through May).
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4.0 GEOLOGIC HAZARD AREAS
4.1 General
According to Chapter 23.80 in the City of Edmonds Municipal Code geologic hazard areas
include "areas susceptible to erosion, land sliding, earthquake, or other geological events. They
pose a threat to the health and safety of citizens when incompatible development is sited in areas
of significant hazard. Such incompatible development may not only place itself at risk, but also
may increase the hazard to surrounding development and use. Areas susceptible to one or more of
the following types of hazards shall be designated as a geologically hazardous area:
A. Erosion hazard;
B. Landslide hazard; and
C. Seismic hazard. [Ord. 4026 1 (Att. A), 2016; Ord. 3527 2, 2004]."
4.2 Landslide
According to the City of Edmonds Municipal Code 23.80.020, landslide hazard areas are defined
as: "areas potentially subject to landslides based on a combination of geologic, topographic, and
hydrologic factors. They include areas susceptible because of any combination of soil, slope
(gradient), slope aspect, structure, hydrology, or other factors. Within the city of Edmonds
potential landslide hazard areas include:
l . Areas of ancient or historic failures in Edmonds which include all areas within the
earth subsidence and landslide hazard area as identified in the 1979 report of Robert
Lowe Associates and amended by the 1985 report of GeoEngineers, Inc., and further
discussed in the 2007 report by Landau Associates;
2. Coastal areas mapped as class u (unstable), uos (unstable old slides), and urs
(unstable recent slides) in the Department of Ecology Washington coastal atlas;
3. Areas designated as quaternary slumps, earthflows, mudflows, or landslides on maps
published by the United States Geological Survey or Washington State Department
of Natural Resources;
4. Any slope of 40 percent or steeper that exceeds a vertical height of 10 feet over a 25-
foot horizontal run. Except for rockeries that have been engineered and approved by
the engineer as having been built according to the engineered design, all other
modified slopes (including slopes where there are breaks in slopes) meeting overall
average steepness and height criteria should be considered potential landslide hazard
areas);
5. Any slope with all three of the following characteristics:
a. Slopes steeper than 15 percent;
b. Hillsides intersecting geologic contacts with a relatively permeable
sediment overlying a relatively impermeable sediment; and
C. Springs or ground water seepage;
6. Any area potentially unstable as a result of rapid stream incision or stream bank
erosion;
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7. Any area located on an alluvial fan, presently subject to, or potentially subject to,
inundation by debris flow or deposition of stream -transported sediments; and
8. Any slopes that have been modified by past development activity that still meet the
slope criteria."
Based on our document research, we found no areas on the site mapped as areas of historic slope
failures. The site is not located along a shoreline and therefore is not mapped by the Washington
State Department of Ecology Coastal Zone Atlas. The United States Geological Survey and the
Washington State Department of Natural Resources maps have not designated any areas as
quaternary slumps, earthflows, mudflows, or landslides. The site does not have a stream running
thru it, therefore no rapid stream incision or stream bank erosion. We did not observe any areas
with topographic expression of runout zones, such as fans and colluvial deposition at the toes of
hillsides. The sites' eastern slope area exceeds 15 percent but have no groundwater seepage or
springs, and do not have intersecting contacts with a relatively permeable sediment overlying a
relatively impermeable sediment. The sites' eastern slope area exceeds 40 percent and has a
vertical height of over 10 feet for a 25-foot horizontal run. The sites' eastern slope area may have
been cut to its current inclination by past grading activities on the site.
Based on the current inclination of the sites' eastern slope area exceeding 40 percent, the site is
classified as a landslide hazard area. However, the site is underlain with medium dense to dense
sand with silt and trace amounts of gravel consistent with Advance Outwash that will exhibit a
relatively high shear strength and low compressibility, even in a sloping environment. We
estimate the friction angle of the native Advance Outwash sands is approximately 36-degrees
with cohesion of approximately 200 psf. And based on our site measurements, the sites' eastern
slope area in inclined at an approximate 30-degree angle. Based on these parameters, the slope is
currently at an angle that is less than the soils friction angle. A soils friction angle is based on the
principle that when a soil is gradually piled, the natural side slopes of the pile will be
representative of the soils friction angle. If piles steeper than the friction angle are made, and no
other factor are present, the soil will eventually erode until its side slope equal its friction angle.
The natural cohesion of the soil will increase the internal strength of the soil allowing it to stand
stable at a much steeper configuration. Based on these factors, we expect the sites' eastern slope
is stable from a global perspective. Provided surface water is controlled on the site, and all
structures are provided with proper subsurface drainage measures, the potential for a landslide to
occur at this site should be considered very low.
4.3 Seismic
According to the City of Edmonds Municipal Code 23.80.020, the City of Edmonds defines
seismic hazard areas as, "In addition to liquefaction -prone areas described in subsection 2 above,
seismic hazard areas are the following:
a. Areas of the City subject to ground shaking from seismic hazards that are addressed by
the Building Code (SMC Title 22).
b. The Seattle Fault zone as delineated in Troost et al., 2005, The geologic map of Seattle, a
progress report, U.S. Geological Survey, Open -file report 2005-1252 or as the Director
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determines is more accurately mapped by the U.S Geological Survey, as set out in a
Director's Rule."
The site is located north of the Seattle Fault zone. The site is located in an area underlain with
medium dense to dense compact glacially consolidated soils.
Liquefaction can be described as a phenomenon where there is a reduction or complete loss of
soil strength due to an increase in pore water pressure. The increase in water pressure is typically
induced by vibrations. Liquefaction mainly affects geologically recent deposits of loose, fine-
grained sands that are below the groundwater table.
Based on the relative density, medium -grained sand and silt content of the soils underlying the
site, and the lack of groundwater the risk for liquefaction to occur at the site should be considered
negligible.
The state of Washington has adopted the International Building Code (IBC). Based on the soil
conditions encountered and the local geology, per the (IBC) site class "D" can be used in
structural design. This is based on the inferred range of SPT (Standard Penetration Test) blow
counts for the upper 100 feet of the site relative to hand excavation progress and probing with a
%2-inch diameter steel probe rod. The presence of glacially consolidated soil conditions were
assumed to be representative for the site conditions beyond the depths explored.
4.4 Erosion
According to the City of Edmonds Municipal Code 23.80.020, defines an Erosion Hazard Area as
"those areas identified by the U.S. Department of Agriculture's Natural Resources Conservation
Service as having a "moderate to severe," "severe," or "very severe" rill and inter -rill erosion
hazard. Erosion hazard areas are also those areas impacted by shoreland and/or stream bank
erosion. Within the city of Edmonds erosion hazard areas include:
Those areas of the city of Edmonds containing soils that may experience severe to very
severe erosion hazard. This group of soils includes, but is not limited to, the following
when they occur on slopes of 15 percent or greater:
a. Alderwood soils (15 to 25 percent slopes);
b. Alderwood/Everett series (25 to 70 percent slopes);
C. Everett series (15 to 25 percent slopes);
2. Coastal and stream erosion areas which are subject to the impacts from lateral erosion
related to moving water such as stream channel migration and shoreline retreat;
3. Any area with slopes of 15 percent or greater and impermeable soils interbedded with
granular soils and springs or ground water seepage; and
4. Areas with significant visible evidence of ground water seepage, and which also include
existing landslide deposits regardless of slope.
The site is mapped as Alderwood gravelly sandy loam (15 to 25 percent slopes) which has a
moderate to severe potential for erosion when exposed. Based on the USDA classification of the
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site, the sites' eastern slope area is classified as an erosion hazard area. No development is
planned in the sloping eastern end of the site.
Temporary Erosion and Sediment Control (TESL) measures must be in place prior to and
maintained during construction activity at the site. In our opinion, the potential for erosion is not
a limiting factor in site development. Erosion hazards can be mitigated by applying Best
Management Practices (BMPs) outlined in the Washington State Department of EcoIogy's
(Ecology) Stormwater Management Manual for Western Washington. TESC measures, in
accordance with the City of Edmonds, must be in place prior to beginning construction on the
site.
5.0 CONCLUSIONS AND RECOMMENDATIONS
5.1 General
Based on our study, in our opinion, soil and groundwater conditions at the site are suitable for the
proposed development. The new retaining wall can be supported on the existing organic -free
native site soils observed immediately below the ground surface, or on structural fill placed above
these native soils.
Our study indicates the native surface soils encountered at the site contain a relatively low
percentage of fines (silt and clay -size particles) that will make them suitable to compact as
structural fill in most weather conditions. Accordingly, the ability to use the soils from site
excavations as structural fill will depend on their moisture content and the prevailing weather
conditions at the time of construction. If grading activities are planned during the wet winter
months, or the on -site soils become too wet to achieve adequate compaction, the owner should be
prepared to import a wet -weather structural fill.
The following sections provide detailed recommendations regarding these issues and other
geotechnical design considerations. These recommendations should be incorporated into the final
design drawings and construction specifications.
5.2 Slone Stability Analysis
To verify the stability of the site before, during, and after the planned development, we performed
a Slope Stability Analysis. The computer program WinStabl was used to determine the overall
stability of the site in its current configuration and for both static and seismic conditions in the
pre -development, during -development and the post -development configuration. The during -
development model included a surcharge for the soil stockpile equivalent to 600 pounds per
square foot (psf) over a 10-foot wide area. The Ultra -block wall was left off of the post -
development model to show the stability of the site is maintained without the wall, and the wall is
for the sole purpose of granting access to the structure. Additionally, the wall design includes a
Slope Stability Analysis.
Slope failure surfaces were analyzed using the Bishop Circular Method. All calculations were
performed by the computer model WmStabl, which requires user input of the topographic
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surface, soil strength properties, groundwater information, and other loads, including seismic and
building loads. The surface data was provided by the topographic site plan, the King County
ArcGIS Map, and our observations and measurements in the field. The soil parameters used in the
analysis are interpreted, estimated, and/or assumed based on our visual observations, field and
laboratory testing, empirical correlations, and experience with similar soil and groundwater
conditions in the vicinity of the subject site.
Once the parameters have been determined, the critical failure surfaces and associated factors of
safety for the modeled slope and development conditions can be calculated. The critical surface is
the surface or plane most likely along which the soil mass will slide. The factor of safety is the ratio
of the sum of moments resisting movement over the sum of moments driving movements.
Accordingly, a slope with a factor of safety less than 1.0 has more driving forces than resisting
forces, while a factor of safety greater than 1.0 has more resisting forces than driving forces.
Industry standard requires that the post -development site conditions have a factor of safety of 1.5
and 1.2 against failure for static and seismic conditions, respectively for the pre -development and
post -development conditions.
To analyze the stability of the site, we performed our analysis on the slopes observed extending
through the center of the site. Based on our site observations, provided site topography, and
encountered subsurface soil and groundwater conditions, we established both dry and saturated
unit weight, isotropic strength intercept (cohesion), and isotropic strength angle (phi angle) for
the various soil types.
Ages Engineering assigned soil unit weight and strength parameters based on our experience, field
explorations accomplished on this site, as well as index laboratory testing accomplished on this
parcels and adjacent properties. Based on our review, we conclude the assumed values for the
various soil types appear to fall well within the range of tabulated values in the literature, and in
some instances, the values appear to be conservative. To accommodate the loose surface soils, we
lowered many of the soil parameters to more conservative levels. The following table summarized
our assigned soil strength properties.
Estimated Properties of On -Site Soils
Dry Unit
Sat. Unit
Isotropic
Internal
Soil Type
Weight
Weight
Strength
Strength
(pcf)
(pcfl
Intercept
Angle
(psi)
(degrees)
Surface: Medium dense SAND
125
130
0
32
with silt and gravel
Weathered Advance Outwash:
Medium dense SAND with silt
125
130
100
34
and gravel
Advance Outwash: Medium
130
135
500
35
dense SAND with silt and gravel
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The site seismic stability conditions were analyzed by applying a horizontal acceleration equal to
one-half of the appropriate peak ground acceleration. Based on current standard of practice, we
used a design peak ground acceleration of 0.195g for the site.
Table l summarizes soil properties, based on site explorations, "Geotechnical and Foundation
Engineering, Design and Construction", by Robert W. Day, copyright 1999 by The McGraw Hill
Companies Inc., and based on "Geotechnical Properties of Geologic Materials", by Koloski,
Schwarz, and Tubbs, Washington Division of Geology and Earth Resources Bulletin 78, as
presented in Volume 1, ENGINEERING GEOLOGY IN WASHINGTON.
Using the Bishop Circular method, we generated several failure surfaces for the pre-, during- and
post -development conditions using both the static and seismic loading conditions. Our analyses
yielded the following safety factors:
Calculated Factor of Safety
Development Condition
Factor of Safety
Pre -Development (Static)
1.8
Post -Development (Static)
1.8
Post -Development (Seismic)
1.2
Graphical output of the WinStabl analysis, indicating the ten most critical failure planes and
corresponding factors of safety for the static and seismic conditions of the pre -development,
during -development, and the post -development models are included in Figures 4 through 6.
5.3 Development in Potential Landslide Hazard Areas
According to the City of Edmonds Municipal Code 23.80.060 - General Requirements,
"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."
Additionally, According to the City of Edmonds Municipal Code 23.80.070 - Development
Standards, "Erosion and Landslide Hazard Areas. Activities on sites containing erosion or
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landslide hazards shall meet the requirements of ECDC 23.80.060, Development standards —
General requirements, and the specific following requirements:
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;
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;
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;
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;
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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;
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;
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 1 st to October I st 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
8. Prohibited Development. On -site sewage disposal systems, including drain fields, shall be
prohibited within erosion and landslide hazard areas and related buffers."
Alterations,
Based on our evaluation, the planned retaining wall replacement will not increase the threat of the
geological hazard to adjacent properties beyond predevelopment conditions. The pre -
development condition consisted of an old wooden retaining wall that was rotted and falling over.
The new retaining wall will consist of the CornerStone Retaining Wall System, constructed with
adequate factors of safety that will render it more stable than the previous rooted wooden wall.
Based on the new wall being more stable than the wall that previously occupied the area, the new
development will not increase the threat of the geological hazard to adjacent properties beyond
predevelopment conditions.
Ages Engineering, LLC Page Lt
253-845-7000
Based on our evaluation, it is our opinion, the new development will not adversely impact other
critical areas. Based on our site evaluation, there are no other critical areas on or immediately
adjacent the construction area. Based on their being no other critical areas on or immediately
adjacent the building area, the new development will not adversely impact other critical areas.
Based on our evaluation, it is our opinion, the new development is designed so that the hazard to
the project is mitigated to a level equal to or less than predevelopment conditions. The pre -
development condition consisted of an old wooden retaining wall that was rotted and falling over.
The new retaining wall will consist of the ComerStone Retaining Wall System, constructed with
adequate factors of safety that will render it more stable than the previous rooted wooden wall.
Based on the new wall being more stable than the wall that previously occupied the area, the new
development is designed so that the hazard to the project is mitigated to a level equal to or less
than predevelopment conditions.
Based on our evaluation, it is our opinion, as a qualified engineer, licensed in the state of
Washington, the new development is safe as designed and under anticipated conditions.
Specific Hazards,
Since the new development consists of the replacement of an old rotted failing wooden retaining
wall with a segmental block wall along the toe of a potential landslide hazard area, the minimum
setback and buffer must be reduced to zero. If the old failing wall is to be replaced, it should be
replaced with a better wall in approximately the same location. In this manner, we can assure an
increase in site stability due to the new development.
Based on our evaluation, it is our opinion, the alteration will not increase surface water discharge
or sedimentation to adjacent properties beyond predevelopment conditions. The old wall allowed
sheet flow over the top of the wall that eventually flowed into the roadside swale adjacent the site.
The new wall will have a wall drain that will discharge to a stabilized location in the existing
roadside Swale adjacent the site. The surface water discharge will be the same in post
development as it was in pre -development. The sedimentation will also be the same.
Based on our evaluation, it is our opinion the alteration will not decrease slope stability on
adjacent properties. According to the slope stability analysis provided in the previous section of
this report,
Based on our evaluation, it is our opinion, the new development will not adversely impact other
critical areas. Based on our site evaluation, there are no other critical areas on or immediately
adjacent the construction area. Based on their being no other critical areas on or immediately
adjacent the building area, the new development will not adversely impact other critical areas.
5.4 Site Preparation and Gradin
To prepare the site for construction, all vegetation, organic surface soils, and other deleterious
materials including any existing structures, foundations or abandoned utility lines should be
stripped and removed from the new development areas. Organic topsoil will not be suitable for
use as structural fill but may be used for limited depths in non-structural areas.
Ages Engineering, LLC Page 12
253-845-7000
Once clearing and stripping operations are complete, cut and fill operations can be initiated to
establish desired grades. In order to achieve proper compaction of structural fill, and to provide
adequate foundation and floor slab support, the native subgrade must be in a stable condition.
Prior to placing structural fill, and to prepare the foundation subgrade, all exposed surfaces should
be compacted with heavy vibratory compaction equipment to determine if any isolated soft and
yielding areas are present.
If excessively soft or yielding areas are present, and cannot be stabilized in place by compaction,
they should be cut to firm bearing soil and filled to grade with structural fill. If the depth to
remove the unsuitable soil is excessive, using a geotextile fabric can be considered, such as
Mirafi HP270 or an approved equivalent, in conjunction with structural fill. In general, a
minimum of 1 S-inches of clean, granular structural fill over the geotextile fabric should establish
a stable bearing surface.
A representative of Ages Engineering, LLC should observe the foundation subgrade compaction
operations to verify that stable subgrades are achieved for support of structural elements.
Our study indicates the native surface soils encountered at the site contain a sufficient enough
percentage of fines (silt and clay -size particles) that will make them difficult to compact as
structural fill when too wet. Accordingly, the ability to use the soils from site excavations as
structural fill will depend on their moisture content and the prevailing weather conditions at the
time of construction. If grading activities are planned during the wet winter months, or the on -
site soils become too wet to achieve adequate compaction, the owner should be prepared to
import a wet -weather structural fill. For wet weather structural fill, we recommend importing a
granular soil that meets the following gradation requirements:
U. S. Sieve Size
Percent Passing
6 inches
100
No. 4
75 maximum
No. 200
5 maximum*
* Based on the'/a inch fraction
Prior to use, Ages Engineering, LLC should examine and test all materials to be imported to the
site for use as structural fill.
Structural fill should be placed in uniform loose layers not exceeding 12 inches and compacted to
a minimum of 95 percent of the soils' laboratory maximum dry density as determined by
American Society for Testing and Materials (ASTM) Test Designation D-1557 (Modified
Proctor). The moisture content of the soil at the time of compaction should be within two percent
of its optimum, as determined by this same ASTM standard. In non-structural areas, the degree
of compaction can be reduced to 90 percent.
Ages Engineering, LLC Page 13
253-845-7000
5.5 Excavations
General,
The inclination for a safe and stable excavation slope cut is determined based on two factors, the
current Washington State Safety and Health Administration (WSHA) regulations for confined
spaces and global stability of the slope cut. Most often, the WSHA regulations are more
conservative than the global stability requirements.
According to WAC 296-809-099, a confined space is defined as: "A space that is all of the
following:
(a) Large enough and arranged so an employee could fully enter the space and work.
(b) Has limited or restricted entry or exit. Examples of spaces with limited or restricted
entry are tanks, vessels, silos, storage bins, hoppers, vaults, excavations, and pits.
(c) Not primarily designed for human occupancy."
In the context of site excavation and grading, the Washington State Department of Labor and
Industries considers a confined space as a space in which a worker enters an excavation that is tall
enough and/or narrow enough to inundate the worker and cause bodily harm if a cave-in occurs.
This does not include excavations that are less than 4.0 feet in depth.
WSHA Approved Slopes,
All excavations at the site associated with confined spaces, such as utility trenches and lower
level building and retaining walls, must be completed in accordance with local, state, and/or
federal requirements. Based on current Washington State Safety and Health Administration
(WSHA) regulations, the existing near -surface loose medium dense old fill soils and the medium
dense Advance Outwash soils would be classified as Type C soils. The deeper dense native sand
with silt and trace gravel soils would be classified as Type B soils.
According to WSHA, for temporary excavations of less than 20 feet in depth, the side slopes in
Type C soils should be laid back at a slope inclination of 1.5:1 (Horizontal:Vertical) or flatter
from the toe to the crest of the slope and the side slopes in Type B soils should be laid back at a
slope inclination of 1:1 (Horizontal:Vertical) or flatter from the toe to the crest of the slope. All
exposed slope faces should be covered with a durable reinforced plastic membrane during
construction to prevent slope raveling and rutting during periods of precipitation. These
guidelines assume that all surface loads are kept at a minimum distance of at least one half the
depth of the cut away from the top of the excavation slope and that significant seepage is not
present on the slope face. Flatter cut slopes will be necessary where significant raveling or
seepage occurs, or if construction materials will be stockpiled along the slope crest. If these safe
temporary slope inclinations cannot be achieved due to property line constraints, shoring may be
necessary.
This information is provided solely for the benefit of the owner and other design consultants and
should not be construed to imply that Ages Engineering, LLC assumes responsibility for job site
safety. It is understood that job site safety is the sole responsibility of the project contractor.
Ages Engineering, LLC Page 14
253-845-7000
Non-W.SM Approved .Slopes,
Based on the composition and consistency of the site soils, stable slope cuts to provide adequate
global stability can be steeper than WSHA standards in areas that are not considered confined
spaces. Excavations into the native site soils that will not result in WSHA regulated confined
spaces can be cut to an inclination of 0.5:1. Some raveling of the gravel and cobbles exposed on
the slope surface may occur at an inclination of 0.5:1. Due to the potential for raveling to occur,
and to prevent erosion, the slope face should be covered with durable plastic sheeting.
This information is provided solely for the benefit of the owner and other design consultants and
should not be construed to imply that Ages Engineering, LLC assumes responsibility for job site
safety. It is understood that job site safety is the sole responsibility of the project contractor.
5.6 ComerStone® Retainine Wall
The new wall will consist of the ComerStone® Retaining Wall System. The wall will be
constructed along the east side of the driveway to the existing residence on the site. The new
retaining wall will support the native Advance Outwash soils exposed in the cut slope along the
east side of the driveway to the existing residence on the site. The new retaining wall should be
constructed according to the manufacturers' specifications and the recommendations provided in
this report. We recommend the following be incorporated into the construction of the wall:
• We recommend using the ComerStone® F 100 and/or ComerStone® F200 blocks.
• The wall batter should be in accordance with the ComerStone® Wall Solutions system.
• The walls should have maximum total heights of no more than those provided in this
report.
• If a cap block is used, it must be entirely above ground and as such will not be considered
in the total height of the wall.
• A minimum of 6 inches (0.75 full blocks) of toe embedment is necessary for erosion
protection and stability purposes.
• A 4 to 6-inch thick layer of crushed rock can be placed along the wall subgrade to
provide a leveling course if desired, but is not necessary.
• The soil used in the backfill zone must consist of structural fill as described in the Site
Preparation and Grading section of this report. The native soils can be used as structural
fill in most weather conditions.
• A drainage layer consisting of 7/8 to 1 1/4 inch clean crushed rock or drain rock with a
minimum horizontal thickness of 12 inches should be placed behind the blocks and up to
the top of the wall, or to within 12 inches of the top of the wall.
• A layer of separation fabric can be placed over the top of the 12-inch wide drainage zone.
No other separation fabric should be used.
• The upper 12 inches of fill may contain organic -laced soil.
• The wall drain should outfall at the low point in the center or at the end of the wall, or
through the base of the wall at a convenient location (1 block above the base block) and
discharge into the sites' storm water system catch basin located to the southeast of the
wall.
Ages Engineering, LLC Page 15
253-845-7000
Wall Design,
The ComerStone® F 100 blocks require geogrid reinforcement for any wall that exceeds 4.5 feet
(7 Blocks) in total height. The ComerStone® F200 blocks require geogrid reinforcement for any
wall that exceeds 6.50 feet (10 Blocks) in total height. Based on our examination of the cut slope
on the site, it appears the wall may have a maximum total height of 4.00 feet and therefore the
FIN blocks can be used. If the wall exceeds 4.5 feet in total height, the F200 blocks must be
used. The tallest portion of the wall will be along the northern end where it meets the existing
concrete retaining wall.
Based on these expected loading conditions, we performed calculations for all these expected
wall heights and are providing calculations for the tallest wall section that can support the
ComerStone® F l 00 blocks and the tallest section that can support the ComerStone® F200
blocks. The wall calculations were performed using the ComerStone® Wall Solutions software
and are provided in Appendix B of the report.
Wall Drainage,
To guard against hydrostatic pressure development, drainage must be installed behind the wall.
We recommend that wall drainage consist of a minimum 12 inches of clean 7/8 to 1 '/4 inch clean
crushed rock or drain rock with less than three percent fines placed against the back of the wall. In
addition, a drainage collector system consisting of 4-inch perforated PVC pipe should be placed
behind the wall to provide an outlet for any accumulated water. The drain should be provided
with a vertical cleanout at each end of the wall alignment. These cleanouts should be serviced at
least once every year. The wall drainage material can be capped at the ground surface with 1-foot
of relatively impermeable soil to prevent surface intrusion into the drainage zone. The wall drain
should outfall at the low point at the end of the wall and discharge to a stabilized area on the
ground surface, or to the site storm water system.
5.7 Permanent Slopes and Embankments
All permanent cut and fill slopes should be graded with a finished inclination of no greater than
2:1 (Horizontal:Vertical). Upon completion of grading, the slope face should be appropriately
vegetated or provided with other physical means to guard against erosion. Final grades at the top
of the slope must promote surface drainage away from the slope crest. Water must not be
allowed to flow in an uncontrolled fashion over the slope face. If it is necessary to direct surface
runoff towards the slope, it should be controlled at the top of the slope, piped in a closed conduit
installed on the slope face, and taken to an appropriate point of discharge beyond the toe.
All fill used for slope and embankment construction should meet the structural fill requirements
described in the Site Preparation and Grading section of this report. In addition, if new fills will
be placed over existing slopes of 20 percent or greater, the structural fill should be keyed and
benched into competent slope soils.
Ages Engineering, LLC Page 16
253-845-7000
6.0 ADDITIONAL SERVICES
Ages Engineering, LLC should review the final project designs and specifications in order to
verify that earthwork and foundation recommendations have been properly interpreted and
incorporated into project design. If changes are made in the loads, grades, locations, configura-
tions or types of facilities to be constructed, the conclusions and recommendations presented in
this report may not be fully applicable. If such changes are made, we should be given the
opportunity to review our recommendations and provide written modifications or verifications, as
necessary.
We should also provide geotechnical services during construction to observe compliance with our
design concepts, specifications, and recommendations. This will allow for expedient design
changes if subsurface conditions differ from those anticipated prior to the start of construction.
7.0 LIMITATIONS
We prepared this report in accordance with generally accepted geotechnical engineering
practices. No other warranty, expressed or implied, is made. This report is the copyrighted
property of Ages Engineering, LLC and is intended for the exclusive use of Mr. Brett Buehler and
his authorized representatives for use in the design, permitting, and construction portions of this
project.
The analysis and recommendations presented in this report are based on data obtained from others
and our site explorations, and should not be construed as a warranty of the subsurface conditions.
Variations in subsurface conditions are possible. The nature and extent of which may not become
evident until the time of construction. If variations appear evident, Ages Engineering, LLC
should be requested to reevaluate the recommendations in this report prior to proceeding with
construction. A contingency for unanticipated subsurface conditions should be included in the
budget and schedule. Sufficient monitoring, testing and consultation should be provided by our
firm during construction to confirm that the conditions encountered are consistent with those
indicated during our exploration, to provide recommendations for design changes should the
conditions revealed during the work differ from those anticipated, and to evaluate whether
earthwork and foundation installation activities comply with contract plans and specifications.
The scope of our services does not include services related to environmental remediation and
construction safety precautions. Our recommendations are not intended to direct the contractor's
methods, techniques, sequences or procedures, except as specifically described in our report for
consideration in design.
Ages Engineering, LLC Page 17
253-845-7000
Lynnwood
I
Approximate Site Location
0
Ages Engineering, LLC
P. O. Box 935
Puyallup, WA. 98371
Main (253) 845-7000
www.agesengineering.com
r� I
r
I
r
t
Mill Creek
i
I
I
Dk'rtl l
('r'aek
Phrk
Site Vicinity Map
Meadowdale Road Residential
16216 N. Meadowdale Road
Edmonds, Washington
Project No.: A-1479-1 February 2020
Figure 1
00643-9
1i
0
Gu6aG5uGGGG&Gi
KEY:
APPROXIMATE LOCATION OF TEST HOLE TH-1
Ages Engineering, LLC
P. O. Box 935
Puyallup. WA. 98371
Main (253)845-7000
www.agesenginecring.com
Exploration Location Plan
Meadowdale Road Residential
16216 N. Meadowdale Road
Edmonds, Washington
Project No.: A-1479-1 1 February 2020 1 Figure 2
Approximate Site Location
Ages Engineering, LLC
P. O. Box 935
Puyallup, WA. 98371
Main (253) 845-7000
www.agesengineering.com
Geologic Map
Meadowdale Road Residential
16216 N. Meadowdale Road
Edmonds, Washington
Problem 16216 N Meadowdale Road - FS Min- Bishop = 1 853
S.ft Ca —wn Fmfi-
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,SC .Feet.
Ages Engineering, LLC Slope Stability Analysis — Static
P. o. Box 935 Meadowdale Road Residential
Puyallup, WA. 98371 16216 N. Meadowdale Road
Main (253) 845-7000 Edmonds, Washington
www.agesengineering.com
Project No.: A4479-1 February 2020 Figure 4
Problem 16216 N Meadowdale Road - FS Min- Bishop = 1 208
M,y
32 1 two 3.a
sw a 35 01
'2 SWII-2
tt Swb..3
S.I..
5.f_ S
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S.H_ to
90
as
70
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2C -lE _101 3 10 to ZI) 2. 20 3! -C fC Ef 6C SE 70 aC 2! 9C 9! IOC 10! IIC IIE t.1 12E IaC la5 113 W M IS: 160 165 170 1?5 150 M IN 195 200 205 210 21E 220 22s 230
Ages Engineering, LLC Slope Stability Analysis — Seismic
P. O. Box 935 Meadowdale Road Residential
Puyallup, WA. 98371 16216 N. Meadowdale Road
Main (253) 845-7000 Edmonds, Washington
www.agesenginee6n.com
Project N February A- 14 79-1 2020Figure 5
APPENDIX A
FIELD EXPLORATION AND LABORATORY TESTING
Meadowdale Road Residential
Edmonds, Washington
On February 22, 2019 we explored subsurface conditions at the site by excavating two hand -augured test holes to
a maximum depth of 10.0 feet below surface grades. This depth equates to a depth of 3.0 feet below the bottom
of the planned retaining wall. The approximate test hole locations are shown on the Exploration Location Plan
provided in Figure 2.
A geotechnical engineering representative from our office conducted the field exploration, maintained a log of
each test hole and, classified the soils encountered, collected representative soil samples, and observed pertinent
site features. All soil samples were visually classified in accordance with the Unified Soil Classification System
(USCS) described on Figure A-1. The test hole logs are presented on Figure A-2.
Representative soil samples obtained from the test holes were placed in sealed containers and taken to our
laboratory for further examination and testing. The moisture content of each sample was measured and is
reported on the test hole logs.
Project No. A-1479-1
UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GROUP
SYMBOL
GROUP NAME
GRAVEL
GW
Well -Graded GRAVEL
WITH
GRAVEL
< 5 % FINES
GP
Poorly -Graded GRAVEL
GRAVEL
GW-GM
Well -Graded GRAVEL with silt
GW-GC
Well -Graded GRAVEL with clay
WITH
BETWEEN
GP -GM
Poorly -Graded GRAVEL with silt
COARSE
More than 50%
Of Coarse Fraction
Retained on
5 AND 15 %
FINES
GP -GC
Poorly -Graded GRAVEL with clay
GRAINED
No. 4 Sieve
GRAVEL
GM
Silty GRAVEL
SOILS
WITH > 15 %
FINES
GC
Clayey GRAVEL
SAND
SW
Well -Graded SAND
WITH
SP
Poorly -Graded SAND
More than 50%
Retained on
SAND
< 5 % FINES
No. 200 Sieve
SAND
SW-SM
Well -Graded SAND with silt
SW -SC
Well -Graded SAND with clay
WITH
More than 50%
Of Coarse Fraction
Passes
BETWEEN
5 AND 15 %
FINES
SP-SM
Poorly -Graded SAND with silt
SP-SC
Poorly -Graded SAND with clay
No. 4 Sieve
SAND
SM
Silty SAND
WITH > 15 %
FINES
SC
Clayey SAND
FINE
ML
Inorganic SILT with low plasticity
CL
Lean inorganic CLAY with low plasticity
GRAINED
Liquid Limit
Less than 50
OL
Organic SILT with low plasticity
SOILS
SILT AND
CLAY
MH
Elastic inorganic SILT with moderate to high plasticity
More than 50%
Passes
Liquid Limit
50 or more
CH
Fat inorganic CLAY with moderate to high plasticity
Organic SILT or CLAY with moderate to high plasticity
No. 200 Sieve
HIGHLY ORGANIC SOILS
PT
PEAT
NOTES
(1) Soil descriptions are based on visual field and laboratory observations using the classification methods described in ASTM D-2488. Where
laboratory data are available, classifications are in accordance with ASTM D-2487.
(2) Solid lines between soil descriptions indicate a change in the interpreted geologic unit. Dashed lines indicate stratigraphic change within the unit.
(3) Fines are material passing the U.S. No. 200 Sieve.
Ages Engineering, LLC
P. O. Box 935
Puyallup, WA. 98371
Main (253) 845-7000
www.agesengineering.com
Unified Soil Classification System (USCS)
Meadowdale Road Residential
16216 N. Meadowdale Road
Edmonds, Washington
Ages Engineering, LLC
Test Hole TH-1
P.O. Box 935
Puyallup, WA. 98371
Office (253) 845-7000
DATE: February 22, 2019 LCXiGFD BY: BPK ELEv:
Depth Soil Description Notes
(feet) M% Other
0
Tan SAND with silt, medium dense, moist. (SP-SM)
5 -1Tannish -gray SAND with silt, slight cementation, medium dense, moist.
(SP-SM) (Weathered Advance Outwash)
Test hole terminated at 7.0 feet below surface grades.
No groundwater seepage encountered.
Test Hole TH-2
DAre: February 22, 2019 LOGGED BY: BPK ELEV
Depth Soil Description Notes
(feet) M% I Other
0
Tan SAND with silt, medium dense, moist. (SP-SM)
5 -1Tannish -gray SAND with silt, trace gravel, slight cementation, medium
dense, moist. (SP-SM1) (Weathered Advance Outwash)
10
Gray SAND with silt, trace gravel, slight cementation, dense, moist.
(SP-SM) (Advance Outwash)
Test hole terminated at 10.0 feet below surface grades.
No groundwater seepage encountered.
FIGURE A-2 Project Number: A-1479-1
APPENDIX B
CORNERSTONE® RETAINING WALL SYSTEM
Meadowdale Road Residential
Edmonds, Washington
We used the ComerStoneg Wall Solutions design software to design the ComerStone® retaining wall planned on
the subject site. The ComerStone® Wall Solutions design software requires user input of the topographic surface,
soil strength properties, groundwater information, and other loads, including seismic and building loads. The
surface data was provided by the King County ArcGIS Map, and our observations and measurements in the field.
The soil parameters used in the analysis are interpreted, estimated, and/or assumed based on the visual observations,
field and laboratory testing, empirical correlations, and experience with similar soil and groundwater conditions in
the vicinity of the subject site.
Once the parameters have been determined, the critical failure surfaces and associated factors of safety for the
modeled wall configuration are calculated. The critical surface is the surface or plane most likely along which the
soil mass will slide. The factor of safety is the ratio of the sum of moments resisting movement over the sum of
moments driving movements. Accordingly, a wall design with a factor of safety less than 1.0 has more driving
forces than resisting forces, while a factor of safety greater than 1.0 has more resisting forces than driving forces.
Industry standard requires that the wall have a factor of safety of 1.5 against sliding and 1.5 against overturning. A
factor of safety of at least 1.2 is required for seismic conditions.
Project No. A-1479-1
CORNERSTONE
REA Analysis
Project: Meadowdale Road Residential
Location: Site Location
Designer: Ages Engineering
Date: 2/29/2020
Section: Section 1
Design Method: NCMA_09_3rd_Ed, Ignore Vert. Force
Design Unit: Cornerstone 200
SOIL PARAMETERS cp coh y
Retained Soil: 35 deg 50 psf 125 pcf
Foundation Soil: 36 deg 100 psf 130 pcf
Leveling Pad: Crushed Stone
GEOMETRY
Design Height: 4.50 ft
Live Load:
0 psf
Wall Batter[Tilt: 4.50/ 0.00 deg
Live Load Offset:
0.00 ft
Embedment: 0.50 ft
Live Load Width:
0 ft
Leveling Pad Depth: 0.00 ft
Dead Load:
0 psf
Slope Angle: 0.0 deg
Dead Load Offset:
0.0 ft
Slope Length: 0.0 ft
Dead Load Width:
0 ft
Slope Toe Offset: 0.0 ft
Leveling Pad Width:
1.00 ft
Vertical b on Single Depth
FACTORS OF SAFETY
Sliding: 1.50
Overturning:
1.50
Bearing: 2.00
Cornerstone Analysis and Design 5.0.19106
vuCORNERSTONE
. �-.- .DESIGNER
RESULTS
FoS Sliding: 2.49 (fnd)
Bearing: 1152.02
FoS Overturning: 1.59
FoS Bearing: 8.07
Name Elev.[dpth] ka Pa Paq
Paqd
(PaC)
PaT
FSsI(Ivl Pd)
FoS OT
%D/H
CS10 4.00[0.50] 0.214 3 0
0
12�
0
—
10.00
150%
CS10 3.33[l.17] 0.214 18 0
0
27
0
-
10.00
86%
CS10 2.67[l.83] 0.214 45 0
0
42
3
--
92.45
55%
CS10 2.00[2.50] 0.214 84 0
0
58
26
12.24
9.30
40%
CS10 1.33[3.17] 0.214 134 0
0
73
61
30.20
4.06
32%
CS10 0.67[3.83] 0.214 196 0
0
89
108
18.32
2.37
26%
CS10 0.00[4.50] 0.214 271 0
0
104
167
2.49 (2.49)
1.59
22%
Column Descriptions:
ka: active earth pressure coefficient
Pa: active earth pressure
Paq: live surcharge earth pressure
Paqd: dead surcharge earth pressure
(PaC): reduction in load due to cohesion
PaT: sum of all earth pressures
FSsl(lvl Pad): factor of safety for sliding at each layer. (FS sliding below
the leveling
pad)
FSot: factor of safety of overturning about the toe.
%D/H: ratio of based depth to height (warning for narrow walls, < 35%)
CornerStone Analysis and Design 5.0.19106 2
7 CORNERSTONE
"..L WAL DESIGNER
REA Analysis
Project:
Meadowdale Road Residential
Location:
Site Location
Designer:
Ages Engineering
Date:
2/29/2020
Section:
Section 1
Design Method: NCMA_09_3rd_Ed, Ignore Vert. Force
Design Unit:
Cornerstone 200
SOIL PARAMETERS cp coh y
Retained Soil:
35 deg 50 psf 125 pcf
Foundation Soil:
36 deg 100 psf 130 pcf
Leveling Pad:
Crushed Stone
GEOMETRY
Design Height:
6.50 ft
Wall Batter/Tilt:
4.50/ 0.00 deg
Embedment:
0.50 ft
Leveling Pad Depth:
0.00 ft
Slope Angle:
0.0 deg
Slope Length:
0.0 ft
Slope Toe Offset:
0.0 ft
Vertical 6 on Single Depth
FACTORS OF SAFETY
Sliding:
1.50
Bearing:
2.00
Live Load:
0 psf
Live Load Offset:
0.00 ft
Live Load Width:
0 ft
Dead Load:
0 psf
Dead Load Offset:
0.0 ft
Dead Load Width:
0 ft
Leveling Pad Width:
1.83 ft
Overturning: 1.50
CornerStone Analysis and Design 5.0,19106
L a
CORNERSTONE
MIER7t"' W A L L D E S I G N E R
CS20
� CS20
CS20
<;
CS20
RESULTS
CS20
FoS Sliding: 2.41 (fnd)
FoS Overturning:
2.03
1 83
Bearing: 1254.97
FoS Bearing:
9.39
Name Elev.[dpth] ka Pa
Paq Paqd
(PaC)
PaT
FSsI(Ivl Pd)
FoS OT
%D/H
CS20 6.00[0.50] 0.214 3
0 0
12
0
—
10.00
275%
CS20 5.33[1.17] 0.214 18
0 0
27
0
-
10.00
157%
CS20 4.67[1.83] 0.214 45
0 0
42
3
100%
C320 4.00[2.501 0.214 84
0 0
58
26
18.95
29.34
73%
CS20 3.33[3.17] 0.214 134
0 0
73
61
9.58
12.57
58%
CS20 2.67[3.83] 0.214 196
0 0
89
108
6.28
7.21
48%
CS20 2.00[4.50] 0.214 271
0 0
104
167
4.63
4.75
41 %
CS20 1.33[5.17] 0.214 357
0 0
119
237
3.65
3.40
35%
CS20 0.67[5.83] 0.214 455
0 0
135
320
7.19
2.57
31 %
CS20 0.00[6.50] 0.214 565
0 0
150
414
2.41 (2.41)
2.03
28%
Column Descriptions:
ka: active earth pressure coefficient
Pa: active earth pressure
Paq: live surcharge earth pressure
Paqd: dead surcharge earth pressure
(PaC): reduction in load due to cohesion
PaT: sum of all earth pressures
FSsI(Ivl Pad): factor of safety for sliding at
each layer. (FS sliding
below the leveling pad)
FSot: factor of safety of overturning about
the toe.
%D/H: ratio of based depth to height (warning for narrow walls, < 35%)
CornerStone Analysis and Design 5.0.19106 2