Geotech Report.pdfGEOTECHNICAL DESIGN & FEASIBILITY EVALUATION
Shell Valley Access Roadway and Short Plat
Main Street to Hidden cove
Edmonds, Washington
ZZA-Terracon Project No. 81085007
May 16, 2008
Prepared for.
Perteet, Inc.
Everett, Washington
Prepared by:
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Bellevue, Washington
May 16, 2008
:..�._.ZZA-1rerracon
Consulting Engineers & Scientists
14405 SE 36ih Streel #210
Bellevue, WA 98006
(425)746-1889 ph
(425) 745-1296 N
www.terraconxom
Perteet, Inc.
2707 Colby Avenue, Suite 900
Everett, Washington 98201
Attention: Mr. Darrell Smith
RE: GEOTECHNICAL DESIGN & FEASIBILITY EVALUATION
Shell Valley Access Roadway and Short Plat
Main Street to Hidden Cove
Edmonds, Washington
Terracon Project No. 81085007
Dear Darrell:
ZZA-Terracon (ZZA) is pleased to submit this report describing the results of our geotechnical
engineering design and feasibility evaluations for the above -referenced project site. Our
geotechnical services were outlined in our proposal letter dated January 11, 2008, and were
formally authorized by your Subconsultant Agreement dated March 5, 2008.
This report is an instrument of service that conforms to locally accepted geotechnical
engineering practice. It has been prepared for the exclusive use of Perteet, Inc„ the City of
Edmonds, and their other consultants, in specific association with the stated project.
We appreciate the opportunity to be of service on this project and would be pleased to discuss
the contents of this report or other aspects of this project with you at your convenience. Please
call if you have any questions or need additional information.
Respectfully Submitted,
1 ferr o
X. Brisbine, P.E., L.G.
e Engineer
Geotechnical Services Group
Distribution: addressee (3 hardcopies + 1 electronic copy)
MON
IN zzAlrerracon
TABLE OF CONTENTS
PROJECTDESCRIPTION.........................................................................................................
l
PURPOSEAND SCOPE............................................................................................................
l
SITESETTING.............................................................................................................................
2
TopographicSetting................................................................................................................
2
DevelopmentalSetting............................................................................................................
3
GeologicSetting....................................................................................................................... 3
RegulatorySetting.................................................................................................................... 3
SITECONDITIONS..................................................................................................................... 3
SurfaceConditions................................................................................................................... 3
DevelopmentalConditions......................................................................................................4
SoilConditions..........................................................................................................................
4
GroundwaterConditions.........................................................................................................
5
SLOPE STABILITY ANALYSIS.................................................................................................
5
Methodof Analysis................................................................................................................... 5
Resultsof Analysis................................................................................................................... 6
CONCLUSIONS AND RECOMMENDATIONS.......................................................................
7
ShortPlat Considerations....................................................................................................... 7
Roadway Preparation and Grading....................................................................................... 8
Roadway Embankment and Pavement................................................................................ 9
Modular Concrete Walls........................................................................................................
l 1
Cast -in -Place Concrete Walls..............................................................................................13
CLOSURE..................................................................... ............
..................................................
16
LIST OF ATTACHMENTS
Figure 1 — Site Location Map
Figure 2 — Site & Exploration Plan
Figure 3 — Site Cross -Section A—A'
Figure 4 — Embankment Edge Diagrams
Figure 5 — Lock -Block Wall Diagrams
Site Photos 1 – 4
Appendix A — Field Exploration Procedures, General Notes, and Logs
Appendix B — Laboratory Testing Procedures and Results
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GEOTECHNICAL DESIGN & FEASIBILITY EVALUATION
Shell Valley Access Roadway and Short Plat
Main Street to Hidden Cove
Edmonds, Washington
ZZA-Terracon Project No. B1085007
May 16, 2008
PROJECT DESCRIPTION
The project site comprises a municipal property located in the Shell Valley neighborhood of
Edmonds, Washington, as shown on the attached Site Location Map (Figure 1). This property
is visually delineated by Main Street on the north, by the Hidden Cove residential development
on the south, and by other residential lots on the west and east. It has a roughly trapezoidal
shape that measures about 250 feet by 300 feet overall. Our attached Site & Exploration Plan
(Figure 2) illustrates the site limits and various adjacent features.
Currently, the project site is substantially vacant and undeveloped, although the site's eastern
margin serves as an easement for several underground utilities. We understand that the
northwestern portion of the site is being used as a long-term storage area for a large quantity of
granular fill soil that was placed by municipal crews during the 1980s. We also understand that
the southeastern corner of the site has been designated as a Class 3 wetland.
Improvement plans by the City of Edmonds call for constructing an emergency access roadway
across the eastern margin of the site. As shown on Figure 2, this new roadway segment will
extend from Main Street southward approximately 250 feet to join an existing roadway near
Hidden Cove. The new roadway section will comprise a 15 -foot -wide asphaltic pavement with
gravel shoulders on each side. Due to the presence of a steep slope on one side and a wetland
on the other, retaining walls might be used along parts of the alignment, but the height of such
walls has not yet been determined. In addition to this roadway construction project, the City is
considering development of the northwestern fill pad as a residential short plat.
PURPOSE AND SCOPE
The purpose of our geotechnical evaluation was to characterize surface and subsurface site
conditions such that we could (1) derive geotechnical design parameters regarding the
proposed roadway, and (2) determine the geotechnical feasibility of developing a short plat on
the northwestern portion of the site. We performed these services in general accordance with
our aforementioned agreement, except where modifications were warranted by project
schedules, access constraints, or client requests. It should be noted that our authorized scope
of services did not include specific design parameters regarding the short plat, nor did it include
a quantitative or qualitative assessment as to the potential presence of regulated environmental
contaminants at the project site. We ultimately completed the following scope items:
• Review of available topographic and geologic maps, municipal documents, and previous
ZZA reports pertaining to the site vicinity;
• A visual surface reconnaissance of the site;
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
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• Four exploratory borings (designated B-1 through B-4) advanced at strategic locations
across the site;
• Laboratory testing of selected soil samples recovered from our explorations,
• Qualitative and quantitative geotechnical engineering analyses regarding the existing
site conditions with respect to the proposed roadway and potential short plat;
• Preparation of this written report.
The locations, elevations, and depths associated with our recent on-site explorations are
summarized in Table 1 and are illustrated on Figure 2. Appendix A describes our field
exploration procedures, and Appendix B describes our laboratory testing procedures.
SITE SETTING
We evaluated the regional setting of the project site by means of published maps, municipal
documents, aerial photos, and previous geotechnical reports. The following text sections
summarize our findings and interpretations regarding the topographic, developmental, geologic,
and regulatory setting of the site.
Topographic Setting
The site is situated within the upper Shell Creek drainage channel, which originates on the
upland plateau of Edmonds. In the site vicinity, this valley forms a U-shaped ravine that trends
southwesterly; closely downstream, the channel turns abruptly to the northwest and forms a V-
shaped ravine that descends toward Puget Sound. Surface grades in the surrounding upland
areas are moderately rolling.
TABLE 1
SUMMARY OF SITE EXPLORATION PROGRAM
Exploration
Functional
Surface
Termination
Location
Elevation
Depth
(feet)
(feet)
B-1
Center of existing fill pad
361
30'/2
B-2
Brink of existing hillslope
361
36
B-3
Bottom of existing hillslope
349
11'2
B-4
Edge of existing wetland
342
16'/2
Note: All exploration depths and elevations should be regarded only as approximate values.
Elevation datum: 2008 survey map provided by Perteet, Inc.
SITE SETTING
We evaluated the regional setting of the project site by means of published maps, municipal
documents, aerial photos, and previous geotechnical reports. The following text sections
summarize our findings and interpretations regarding the topographic, developmental, geologic,
and regulatory setting of the site.
Topographic Setting
The site is situated within the upper Shell Creek drainage channel, which originates on the
upland plateau of Edmonds. In the site vicinity, this valley forms a U-shaped ravine that trends
southwesterly; closely downstream, the channel turns abruptly to the northwest and forms a V-
shaped ravine that descends toward Puget Sound. Surface grades in the surrounding upland
areas are moderately rolling.
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
Developmental Setting
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The site is situated in an area characterized by moderately dense residential development,
along with an extensive network of arterial and neighborhood roadways. It appears that a
sewerline underlies the ravine invert in the site vicinity. Although a Standard Oil easement also
traverses the site vicinity, we understand that no oil or gas pipeline has ever been installed.
Geologic Setting
According to the 1983 Geologic Map of the Edmonds East and Pari of the Edmonds West
Quadrangles, Washington (U.S. Geological Survey publication MF -1541), the project site
straddles a contact between two Quaternary -age glacial deposits. The upper mapped unit
comprises glacial till, which is described as a "hard ... non -sorted mixture of clay, silt, sand,
pebbles, cobbles, and boulders, all in variable amounts" with a thickness generally in the range
of 6 to 50 feet. The lower mapped unit comprises advance outwash, which is described as a
"thick section of mostly clean, gray, pebbly sand with... gravel... and some silt..." with localized
iron -oxide staining. Typically, the glacial till deposit is mantled by a relatively loose layer of
recessional outwash and/or weathered till.
Regulatory Setting
Based on the Edmonds Community Development Code (ECDC), the site vicinity appears to
contain geologically hazardous areas due to the presence of steep slopes (greater than 40
percent). However, the ECDC includes provisions for mitigating factors such as favorable soil
conditions. The presence of glacial till or advance outwash soils, which have been mapped in
the site vicinity, would constitute a significant mitigating factor.
SITE CONDITIONS
ZZA representatives visited the project site on January 3 and March 14, 2008, to evaluate
surface and subsurface conditions. Our geotechnical observations, measurements, findings,
and interpretations are described in the following text sections. The enclosed Site Photos
illustrate various aspects of the site conditions. The enclosed Site Cross -Section (Figure 3)
depicts topographic and stratigraphic conditions through a key part of the site.
Surface Conditions
Local surface grades vary considerably across the site, apparently due to both natural stream
erosion and subsequent artificial filling. The western portion consists of a high plateau with a
relatively flat surface that slopes gently downward to the north; existing vegetation is limited to
low grass with a few trees along the southern edge. We infer that this plateau was created
mainly by municipal filling activities. The eastern portion of the site consists of a low ravine
bottom with a gently concave surface; existing vegetation includes grasses, cattails, bushes,
and scattered mature trees. We observed standing water over most of this ravine bottom at the
time of our site reconnaissance. The high plateau and the ravine bottom are separated by a
steep hillslope that ranges up to about 25 feet high. Slope inclinations range from about 2H:1V
(horizontal: vertical) to as much as '/2H:1 V in localized areas. This hillslope is vegetated with
mature evergreen trees and low -growing plants. We did not observe indications of recent
sloughing or slumping at the time of our reconnaissance.
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
Developmental Conditions
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Existing on-site development, appears to be limited to a sewerline that runs in a roughly north—
south alignment through the ravine bottom, Several manhole covers are visible on the ground
surface. There is also a large (about 6 -foot -diameter) culvert that extends underneath Main
Street to serve as a pedestrian crossing.
Soil Conditions
Our on-site exploratory borings revealed subsurface conditions that generally conform to the
published mapping designation of advance outwash soil and to our localized surface
interpretations of fill soils. None of our borings appeared to encounter glacial till, indicating that
this deposit probably lies at a somewhat higher elevation. Table 2 summarizes the stratigraphic
data obtained from our on-site exploratory borings, and Figure 2 shows the relative field
locations of these borings. Figure 3 schematically illustrates our interpretation of subsurface
stratigraphy. Appendix A presents our stratigraphic logs, and Appendix B presents our
laboratory testing results.
Borings B-1 and B-2, which were advanced on the northwestern plateau, disclosed about 14'/2
to 17 feet of fine to coarse sands and gravels with varying amounts of silt and cobbles. We
interpret these surficial soils to be artificial fill that was placed here by municipal crews. The fill
ranged from loose to dense, with the lowest densities occurring at depths around 10 feet below
existing grades. Both borings encountered medium dense to very dense sands and gravels,
which we infer to be advance outwash, underlying the fill deposit and extending downward to
the drilling termination depths of 30 to 36 feet.
Borings B-3 and B-4, which were advanced in the ravine bottom, encountered about 4 feet of
medium stiff sandy silts and loose silty sands mantling the surface. We interpret these soils to
be colluvium derived from upslope areas. B-4 also penetrated about 6'/ feet of mottled, loose,
silty sands, which we infer to be a lower fill or alluvial layer. Underlying the surficial soils, at
depths starting about 4 to 10'/2 feet below existing grades, we observed medium dense to dense
advance outwash.
TABLE 2
SUMMARY OF STRATIGRAPHIC SITE DATA
Thickness of
Thickness of
Thickness of
Depth to
Exploration
Municipal
Upper
Lower Fill/
Advance
Fill Soil
Colluvial Soil
Alluvial Soil
Outwash
(feet)
(feet)
(feet)
(feet)
B-1
17
0
0
17
B-2
14'/2
0
0
14'/2
B-3
0
4
0
4
B-4
0
4
6%
10'/2
Note: All stratigraphic measurements are based on interpretation of gradual or undulating soil contacts
and should be regarded only as approximate or average values.
Elevation datum: 2008 survey map provided by Perteet, Inc.
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
Groundwater Conditions
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At the time of exploration (March 2008), our two northwestern -plateau borings encountered
groundwater at depths of about 18 and 28 feet below existing grades. These depths lie within
the advance outwash deposit. Our two ravine -bottom borings did not reveal a distinct
groundwater horizon, but the uppermost soils were generally wet. Throughout the year, the on-
site groundwater conditions will likely fluctuate due to seasonal precipitation patterns, on-site or
off-site land use changes, irrigation schedules, and other factors.
SLOPE STABILITY ANALYSIS
In order to quantify construction -phase and post -construction stability conditions of the existing
hillslope at the project site, we analyzed the hillslope under several different graphic models.
The following text sections describe our analytical methods and results.
Method of Analysis
Our hillslope analysis included several scenarios that involve slope gradients of '/2H:lV and
1H:1V, which represent the likely range of temporary cut -slope angles that might be used during
construction. We also evaluated a scenario involving a 10 -foot -high, near -vertical wall, to
represent a severe post -construction case in which a full -height gravity or cantilevered wall is
built at the toe of the hillslope.
For any given slope topography, a stability analysis typically involves five basic subsurface
parameters: (1) location and shape of the potential failure surface, (2) internal friction angle of
the various soils, (3) cohesion of the various soils, (4) density of the various soils, and (5)
location of the piezometric groundwater surface. Because these values are seldom accurately
known at the start of an analysis, they usually must be estimated, interpreted, and/or assumed
on the basis of visual observations, field testing, laboratory testing, empirical correlations, and
experience with similar soil types. Table 3 summarizes the soil properties that we used for this
analysis.
TABLE 3 -
SOIL PROPERTIES USED FOR STABILITY ANALYSIS
Material Type/Purpose
Density
Cohesion
Internal Friction
Angle
(pcf)
(psf)
(degrees)
Retaining Wall (concrete blocks or gabions)
155
>1000
60
Medium -Dense SAND (upper fill soil)
125
25
32
Loose Silty SAND (lower fill soil)
120
25
32
Medium -Dense to Dense SAND
(upper advance outwash)
130
25
36
Dense to Very Dense SAND
(lower advance outwash)
135
25
38
Shell Valley Access Roadway
Edmonds, Washington
81085007
May 16, 2008
ZZA,lrerracon
We analyzed slope stability conditions for the project site using Bishop's Simplified Method of
Slices, which is based on a limit -equilibrium technique. All calculations were performed by
means of the computer program XSTABL. This program utilizes topographic, soil, and
groundwater information input by the user to determine numerous slip surfaces and associated
safety factors. We have assumed that effective drains will be installed behind any new retaining
walls to prevent a build-up of excess hydrostatic pressure. 'By convention, seismic stability
conditions are based on a horizontal acceleration equal to one-half of the appropriate peak
ground acceleration; starting with a peak bedrock acceleration of 0.30g to 0.35g for the site, we
utilized a conservative design value of 0.20g.
Results of Analysis
Based on the subsurface parameters described above, an array of slip surfaces and associated
safety factors was calculated. A critical slip surface is defined as the most likely surface along
which a soil mass will slide, and a safety factor is defined as the ratio of the sum of all moments
resisting slope movement versus the sum of all moments tending to cause slope movement.
Consequently, a slope that possesses a minimum safety factor of 1.0 is on the verge of sliding,
whereas a slope with a minimum safety factor greater than 1.0 possesses some resistance to
sliding. According to standard geotechnical engineering practice, a static safety factor of 1.50
and a seismic safety factor of 1.10 are typically considered the lowest acceptable values for
permanent slopes, whereas significantly lower values are usually acceptable for temporary
slopes.
We subsequently found that the minimum static safety factor corresponding to a '/2HAV
temporary cut slope is less than 1.00, and that the minimum value for a 1H:1V temporary cut
slope is 1.01. In both cases, the sliding mode was a fairly shallow circular surface, indicating
that the soil becomes more slide -resistant with depth; that is, deep-seated slope movements
are highly unlikely. For the case of a 10 -foot -high retaining wall, we found static and seismic
safety factors of 2.05 and 1.34, respectively. The sliding mode was a roughly circular slide
surface that lies closely below the wall base and exits 10 to 15 feet in front of the wall. Table 4
summarizes our calculated safety factors.
TABLE 4
CALCULATED SAFETY FACTORS FOR SELECTED FAILURE SCENARIOS
Failure
Scenario
Sliding
Mode
Static Seismic
Safety Factor Safety Factor
Temporary '/zH:1V Slope
Shallow Circular
<1.00 —
Temporary 1HAV Slope
Shallow Circular
1.01 —
Permanent 10 -foot Wall
Shallow Circular
2.05 1.34
Shell Valley Access Roadway
Edmonds, Washington
61085007
May 16, 2008
CONCLUSIONS AND RECOMMENDATIONS
ffizzAlrerracon
Based on the information obtained from our surface and subsurface exploration program, the
proposed access roadway appears feasible from a geotechnical standpoint, contingent on
proper design and construction practices. The following paragraphs present our general
geotechnical conclusions, recommendations, and comments regarding important development
issues.
Roadway Subgrades: Our exploratory borings disclosed about 4 to 10 feet of silty
sands and sandy silts mantling the proposed roadway alignment. Because these soils
are somewhat compressible and highly moisture -sensitive, special subgrade preparation
is needed to prevent excessive long-term pavement distress.
• Slope Stability: Our stability analysis indicated that the proposed truncation of the
existing hillslope is geotechnically feasible, contingent on construction of an
appropriately designed retaining wall. During wall construction, it appears that a
reasonable temporary cut -slope angle can be maintained behind the wall alignment.
Retaining Walls: To support the truncated hillslope, suitable types would include cast -
in -place concrete cantilever walls, soldier pile cantilever walls, modular concrete gravity
walls, and gabion gravity walls. We anticipate that either a cast -in-place concrete
cantilever wall or a modular concrete gravity wall might be most advantageous, for
reasons of appearance and economy. Gabion walls could also be used to support the
wetland side of the new roadway embankment.
The following text sections present our specific geotechnical conclusions and recommendations
concerning short plat considerations, roadway preparation and grading, roadway embankments
and pavements, modular concrete walls, cast -in-place concrete walls, and structural fill. ASTM
and WSDOT specification codes cited herein respectively refer to the current manual published
by the American Society for Testing & Materials and the current edition of Standard
Specifications for Road, Bridge, and Municipal Construction,
Short Plat Considerations
We understand that the City of Edmonds intends to develop the northwestern plateau as a
residential short plat. Our limited exploration of this area indicated that development of a short
plat might be feasible. We offer the following preliminary comments.
Building Setbacks: Any new structures will need to maintain adequate horizontal setbacks from
the brink of the plateau. We tentatively estimate that a setback on the order of 10 to 20 feet
would be appropriate, depending on the final height and angle of the sideslope. Setbacks could
be reduced by grading the surface down to a lower elevation, constructing retaining walls along
the edge, and/or flattening the sideslopes.
Soil Conditions: Our exploratory borings disclosed that the northwestern plateau is mantled by
about 14'/2 to 17 feet of fill soils comprising fine to coarse sands and gravels with varying
amounts of silt and cobbles. This fill ranged from loose to dense, with the lowest densities
occurring at depths around 10 feet below existing grades. It appears that relatively little
mechanical compaction was used when the fill was placed; more likely, a moderate degree of
7
Shell Valley Access Roadway
Edmonds, Washington
81085007
May 16, 2008
N zzA lrerracan
incidental densification was achieved through some combination of vehicle traffic, percolation,
and self -weight. Our visual evaluation indicated that these soils could be reused for general
structural fill use either on site or off site.
Structure Foundations: In our opinion, future houses and other structures built on the
northwestern plateau could experience undesirably large settlements due to gradual
compression of the loose soils. We tentatively anticipate that the adverse effects of such
settlements could be mitigated through some or all of the following means:
■ Overexcavation of existing fill soils down to an appropriate depth, followed by
replacement and compaction of the same fill soil in a sequence of thin lifts.
■ Surcharging the existing fill surface with a high soil embankment for an appropriate
length of time to induce settlements.
® Improving future foundation subgrade areas by installing short aggregate piers to an
appropriate depth.
■ Supporting new structures on pin piles or concrete piers that extend to an appropriate
depth.
Additional Work: Additional explorations and analyses will be necessary to facilitate actual
design criteria for a future short plat development. Specifically, we recommend that three to five
more borings be advanced through the existing fill and into the underlying native soils.
Roadway Preparation and Grading
Preparation and grading of the new roadway and retaining wall alignments will likely involve
tasks such as temporary drainage, clearing, stripping, cutting, filling, erosion control, and
subgrade compaction. The paragraphs below present our geotechnical comments and
recommendations concerning these various issues.
Temporary Drainage: Any sources of surface or near -surface water that could potentially enter
the construction zone should be intercepted and diverted before stripping or grading activities
begin. We tentatively anticipate that a system of temporary berms or swales placed around the
construction zone will adequately intercept surface water runoff. However, because the
selection of an appropriate drainage system will depend on the water quantity, season, weather
conditions, construction sequence, and contractor's methods, final decisions regarding drainage
systems are best made in the field at the time of construction.
Clearing and Stripping: After surface and near -surface water sources have been controlled, the
construction zone should be cleared and stripped of all trees, bushes, sod, topsoil, debris,
asphalt, and concrete. We anticipate that a minimum stripping depth of 6 inches will be needed
to remove surficial organic soils, but greater depths might be needed in certain areas. A ZZA
representative should be allowed to observe the stripping operation and determine an
appropriate depth. Furthermore, it should be realized that if the stripping operation proceeds
during wet weather, a generally greater stripping depth might be necessary to remove disturbed
moisture -sensitive soils. For this reason, site stripping is best performed during a period of dry
weather.
Shell Valley Access Roadway
Edmonds, Washington
61085007
May 16, 2008
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Roadway Grading: The proposed roadway alignment should be graded as needed to
accommodate the new roadway section. South of the approximate midpoint (near Station
11+50), a cut depth of 2 feet will likely be necessary. North of this point, we anticipate that the
cut depth can be reduced. However, the appropriate cut depth in all areas will depend on actual
soil conditions observed by ZZA at the time of grading.
Erosion Control Measures: Because stripped surfaces and soil stockpiles are typically a source
of runoff sediments, they should be given particular attention. We recommend that silt fences,
berms, and/or swales be installed around the downslope side of stripped areas and stockpiles in
order to capture runoff water and sediment. If earthwork occurs during wet weather, all stripped
surfaces should be covered with straw to reduce runoff erosion, whereas soil stockpiles should
be protected with plastic sheeting. Permanent slopes should be revegetated as soon as
possible to minimize erosion.
Temporary Cut Slopes: All temporary cut slopes associated with the roadway and wall cuts
should be adequately inclined to prevent sloughing and collapse. For the loose to dense sands
and medium stiff silts that will likely be exposed, our slope stability analysis indicated that cut
slope inclinations should be in the range of 1.25H:1 V to 1.OH:1 V (horizontal: vertical). However,
appropriate inclinations will depend on the actual soil and groundwater conditions encountered
during earthwork. Ultimately, the site contractor must be responsible for maintaining safe
excavation slopes that comply with applicable OSHA or WISHA guidelines.
Temporary Dewatering: The potential for groundwater problems within the site excavations will
greatly depend on the soil conditions, the time of year, and the prevailing weather conditions
during earthwork. If only a relatively slow rate of groundwater seepage is encountered, we
anticipate that an internal system of ditches, sumpholes, and pumps will be adequate to
temporarily dewater the excavations.
Roadway Embankment and Pavement
Once the roadway alignment has been stripped and graded, as previously described, the
subgrade can be prepared and the roadway section can be constructed. We offer the following
geotechnical comments and recommendations concerning various design and construction
issues.
Subgrade Compaction: Before any fill material or geotextile is placed, the excavated subgrade
for the new roadway should be compacted to a firm, unyielding state by means of a heavy
static -drum roller. Any localized zones of organic, soft, or pumping soils observed within a
subgrade should be overexcavated and replaced with a suitable structural fill material.
Roadway Section: Based on the observed and anticipated subgrade conditions along the
proposed roadway alignment, we recommend the following minimum roadway section. Each
individual layer is discussed sequentially from bottom to top in the paragraphs below.
Shell Valley Access Roadway
Edmonds, Washington
81085007
May 16, 2008
Roadway Layer
(top to bottom
Asphalt Concrete Pavement
Granular Top Course
Granular Base Course
Embankment Fill
Bearing Blanket
Separation Geotextile
O ZZ lrerfacon
Minimum
Thickness
3 inches
2 inches
3 inches
1 foot
2 feet
Separation Geotextile: To retard upward silt migration from native subgrade soils into any
overlying structural fill, it would be beneficial to cover all subgrade areas with a separation
geotextile. We specifically recommend using a durable woven material, such as Mirafi 500X.
Granular Bearing Blanket: We recommend that a full -width bearing blanket of granular
structural fill material be provided below the new roadway embankment. In our opinion, a well -
graded sand and gravel, such as "Gravel Borrow" or "Ballast" per WSDOT: 9-03.14 or 9-03.9(1),
respectively, would be suitable for this purpose. Alternatively, an angular material such as
"Crushed Surfacing Base Course" per WSDOT: 9-03.9(3) could be used, We recommend
providing a thickness of at least 2 feet; however, the actual thickness will depend on the
stripping and subgrade excavation depths.
Embankment Fill: We understand that it will be necessary to maintain hydraulic conductivity
across the new roadway for the benefit of existing wetland areas. Therefore, the new roadway
embankment should consist of a clean, uniform, coarse-grained, structural' fill material. to our
opinion, a fairly uniform 2 -inch crushed rock (often called "railroad ballast") would be suitable.
We recommend providing a thickness of at least 1 foot, for hydraulic purposes; however, the
actual thickness could be considerably greater, depending on the height of the new roadway
surface above surrounding grades.
Granular Base Course: The granular base course should be sufficiently coarse-grained to
prevent migration into the underlying embankment fill, while providing a suitable bearing layer
for the overlying top course. We specifically recommend using "Crushed Surfacing Base
Course" per WSDOT: 9-03.9(3). The base course should have a minimum thickness of 3
inches.
Granular Too Course: The granular top course serves as a bearing and leveling layer for the
overlying pavement layer. For this purpose, we recommend using "Crushed Surfacing Top
Course" per WSDOT: 9-03.9(3). The top course should have a minimum thickness of 2 inches.
Asphalt Concrete Pavement: For the pavement course, we recommend using standard
WSDOT hot -mix asphalt concrete with %2 -inch -maximum aggregate (known as "HMA -'/Z"). In
our opinion, a pavement thickness of 3 inches would be appropriate, assuming that the roadway
will be limited to occasional use by passenger cars, buses, and emergency vehicles.
Fill Placement and Compaction: All roadway fill material
having a maximum loose thickness of 12 inches. For
thoroughly compacted to a uniform density of at least 90
10
should be placed in horizontal lifts
well -graded fill, each lift should be
percent (based on ASTM: D-1557).
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
zzAlrerracon
For coarse gravels, each lift should be compacted by means of at least three passes with a
heavy, vibratory, smooth -drum or segmented -drum roller.
Embankment Settlements: We estimate that post -construction settlements of the new roadway
embankment could range from about 1 to 3 inches. Actual settlements will ultimately depend on
the final embankment height and the specific soil conditions at any particular location. The
adverse effects of these settlements can be mitigated by deferring the final paving operation
until very late in the construction project, thereby allowing most settlement to occur in advance.
Edge Treatments: If sufficient lateral space is available within the wetland beside the new
roadway, it would be practical to construct the roadway embankment with conventional
permanent sideslopes. On the other hand, if lateral constraints demand that the roadway
footprint be made as narrow as possible, reinforced edges or retaining walls might be required.
Our recommendations concerning these options are discussed below and are illustrated on the
enclosed Embankment Edge Diagrams (Figure 4).
• Conventional Sideslopes: For conventional permanent sideslopes, we recommend that the
face angle be no steeper than 2H:1 V. The use of flatter slopes (such as 3H:1 V) would be
advantageous to further reduce long-term erosion and facilitate revegetation
Retaining Walls: Vertical or near -vertical embankment edges can be maintained by
constructing a retaining wall on one or both sides. Considering the probability of some long-
term differential settlements along the new embankment, we recommend using a flexible
wall type that can accommodate moderate deformations. In our opinion, rock -filled gabion
baskets are well-suited for this purpose. Common sizes of gabion baskets are 3 feet wide
by 3 feet high by 6 or 9 feet long. All gabions should sit directly on the bearing blanket, as
shown on Figure 4. This option is particularly well-suited for wetland crossings that require
both hydraulic connectivity and a minimal roadway footprint.
Reinforced Edges: Sideslope angles in the range of 1 H:1V to'/2H:1V can be maintained by
using geotextiles to reinforce the soil at the embankment edges. We recommend the use of
a strong woven geotextile (such as Mirafi 500X) as an inner wrapping around 12 -inch
(maximum) lifts of embankment soil, combined with an outer wrapping of geogrid (such as
Mirafi 5T) to contain a topsoil infill strip. After completion, the topsoil infill should be
hydroseeded or planted with a hearty groundcover. It should be noted that this option would
not provide as much hydraulic connectivity as the previous two options.
Modular Concrete Walls
In our opinion, a gravity -type modular concrete retaining wall would adequately support the
proposed hillslope cut and allow some additional filling along the edge of the northwestern
plateau, possibly for a lower cost than other wall types. The paragraphs below present our
geotechnical comments and recommendations concerning this wall type, and the enclosed
Lock -Block Wall Diagrams (Figure 5) illustrate many of our recommendations.
Wall Systems: Possible varieties of modular concrete walls include the proprietary Lock -Block
and Kelley -Block systems, both of which comprise heavy precast concrete blocks. A basic
("full") Lock -Block module measures 2'/z feet by 2'/ feet by 5 feet and has two interlocking
features, whereas a basic Kelley -Block module measures 2 feet by 2 feet by 4 feet and has
11
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
O zzlrerracon
eight interlocking features. Both varieties are available with architectural facades. For the
subject site, we have assumed the use of Lock -Blocks because they seem to be more readily
available in the Puget Sound area. If an alternative system is selected for the subject wall, we
might need to re -analyze the wall to account for any differences in the module size or shape.
Subgrade Preparation: Gravity walls must bear on firm, unyielding, non-organic soils to
minimize post -construction settlements and avoid bearing failures. Based on our exploratory
borings, we anticipate that an overexcavation extending approximately 4 feet below existing
grades will be needed to reach adequate bearing soils, but the actual depth should be
determined by a geotechnical field representative. Once suitable bearing soils have been
reached, the overexcavation should be backfilled to subgrade level with compacted structural
fill. We specifically recommend using either 2 -inch angular rock ("railroad ballast") or 2- to 4 -
inch quarry spalls for this purpose.
Embedment Depth: For sliding resistance, as well as frost and erosion protection, the bottom
row of blocks should be embedded at least 18 inches below the adjacent ground surface at the
wall toe. This will require the excavation of an embedment trench along the entire wall
alignment. After completion of the wall, a prism of structural fill (such as 5/8 -inch crushed rock)
should be compacted along the toe, as shown on Figure 5.
Wall Height: We assume that the wall would have a maximum exposed face height of about 10
feet, which includes a 2 -foot -high parapet for catching debris. Given the height of a "full' Lock -
Block module (2'/2 feet) and our recommended embedment depth (1'/Z feet), six rows of blocks
would be required to provide this maximum height, as shown on Figure 5.
End Treatment: If desired, each end of the wall could be stepped down to meet the base grade,
rather than terminating the wall abruptly. Figure 5 illustrates the use of specially shaped
"transition" Lock -Blocks to achieve a more visually attractive step-down configuration, but these
esthetic enhancements can be regarded as optional.
Face Batter: The term batter refers to the intentional inclination of a wall face into the soil bank
behind it, such that the wall appears to be leaning against the bank rather than standing
vertically. For reasons of wall stability and visual esthetics, we recommend that the subject wall
be constructed with a face batter of 1 H:5V (approximately 11 degrees), as shown on Figure 5,
Module Configuration: For a Lock -Block wall comprising six rows of blocks, the first and third
rows should be oriented perpendicular to the cut bank, whereas the other rows can be oriented
parallel to the cut bank, as shown on Figure 5. Our calculations indicate that such a
configuration will provide safety factors of 1.5 or more against sliding and overturning, based on
inferred backslope geometry, assumed soil parameters, and adequate drainage. If the wall is
stepped downward at each end, the lowest row of blocks can be successively eliminated to
accommodate the height decrease.
Drainage and Backfill: Effective drainage behind retaining walls is critical to prevent a buildup of
hydrostatic pressure, and a high-strength backfill material is beneficial for reducing lateral earth
pressure. Consequently, we recommend that the entire void between the wall and soil bank be
backfilled with clean, coarse, angular rock, such as 2 -inch "railroad ballast" or 2- to 4 -inch quarry
spalls. This backfill should extend outward at least 18 inches from the wall to create a curtain
drain, and the surface should be capped with topsoil or some other relatively impervious
12
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
ffiZZA-1rerracon
material. Also, a 4 -inch -diameter perforated drainpipe within a pea gravel envelope should be
placed along the heel of the wall, per Figure 5.
Cast -in -Place Concrete Walls
In our opinion, a cast -in-place concrete cantilever retaining wall would adequately support the
proposed hilislope cut and allow some additional filling along the edge of the northwestern
plateau, although the cost for this would likely be higher than for a gravity -type wall. The
paragraphs below present our geotechnical comments and recommendations concerning this
wall type.
Subgrade Preparation: Cantilevered walls must bear on firm, unyielding, non-organic soils to
minimize post -construction settlements and avoid bearing failures. Based on our exploratory
borings, we anticipate that an overexcavation extending approximately 4 feet below existing
grades will be needed to reach adequate bearing soils, but the actual depth should be
determined by a geotechnical field representative. Once suitable bearing soils have been
reached, the overexcavation should be backfilled to subgrade level with compacted structural
fill. We specifically recommend using either 2 -inch angular rock ("railroad ballast") or 2- to 4 -
inch quarry spalls for this purpose.
Footing Depths and Widths: For frost and erosion protection, all wall footings should bear at
least 18 inches below the adjacent ground surface. However, greater depths might be
necessary to develop adequate passive resistance and/or bearing resistance in certain cases,
as determined by the project structural engineer. To reduce post -construction settlements, all
footings should be at least 36 inches wide.
Bearing Capacities: Based on the dimensional criteria and bearing subgrade conditions
described above, we recommend that all footings be designed for the following maximum
allowable soil bearing capacities. These values incorporate static and transient (wind or
seismic) safety factors of at least 2.0 and 1.5, respectively.
Design Parameter Allowable Value
Static Bearing Capacity 3000 psf
Transient Bearing Capacity 4000 psf
Curtain Drains: A curtain drain is a vertical layer of drainage material that is placed against the
back of a wall to dissipate hydrostatic pressures. Ideally, this curtain drain would consist of pea
gravel, washed rock, or some other clean, uniform, well-rounded gravel, extending outward at
least 18 inches from the wall and extending upward to within about 12 inches of the ground
surface. In all cases, we recommend that a 4 -inch -diameter perforated drainpipe be installed at
the base of the curtain drain.
Backfill Soil: Ideally, all wall backfill placed behind the curtain drain would consist of clean, free -
draining, granular material, such as "Gravel Backfill for Walls" per WSDOT: 9-03.12(2).
Alternatively, on-site granular soils could be used as backfill if they are placed at a moisture
content near optimum. In the event that very silty soils are used as backfill, a filter fabric (such
as Mirafi 140N) should be placed between the granular curtain drain and the backfill soil to
prevent drain clogging.
13
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
zzlrerracon
Backfill Compaction: Because soil compactors place significant lateral pressures on walls, we
recommend that only small, hand -operated compaction equipment be used within 3 feet of a
wall. Also, all backfill should be compacted to a density as close as possible to 90 percent of
the maximum dry density (based on ASTM: D-1557). A greater degree of compaction closely
behind the wall would increase the lateral earth pressure, whereas a lesser degree of
compaction might lead to excessive post -construction settlements.
Grading and Capping: To retard the infiltration of surface water into the backfill soils and curtain
drain, we recommend that the backslope surface of exterior walls be adequately inclined to
route water away from the wall. Ideally, this backfill surface would also be capped with asphalt,
concrete, or 12 inches of low -permeability (silty) soils to reduce or preclude surface water
infiltration.
Applied Loads: All walls should be designed to resist the various lateral loads applied to them.
Based on existing and proposed conditions at the subject site, we expect that these lateral loads
will consist of static pressures, surcharge pressures, and seismic pressures. We do not expect
that hydrostatic pressures will need to be considered if adequate drainage is provided per our
recommendations given above. The following paragraphs present our recommended design
pressures.
Static Pressures: Walls that are allowed to yield slightly during the backfilling operation (such
as cantilevered site walls) should be designed to withstand an appropriate active lateral earth
pressure. In contrast, walls that are restrained against rotation should be designed to withstand
an. appropriate at -rest lateral earth pressure. These pressures act over the entire back of the
wall and vary with the backslope inclination. For various backslope angles (measured
perpendicular to the wall face), we recommend using the following active and at -rest pressures
(given as equivalent fluid unit weights):
Backslope
Active
At -Rest
Angle
Pressure
Pressure
Level
35 pcf
55 pcf
3.OH:1 V
44 pcf
69 pcf
2.OH:1 V
53 pcf
83 pcf
• Surcharge Pressures: Static lateral earth pressures acting on a wall should be increased to
account for surcharge loadings resulting from any traffic, construction equipment, material
stockpiles, or structures located within a horizontal distance equal to the wall height. For
simplicity, a traffic surcharge can be modeled as a uniform pressure of 75 psf acting against
the upper 6 feet of wall.
Seismic Pressures: Static lateral earth pressures acting on a wall should be increased to
account for seismic loadings. These pressures act over the entire back of the wall and vary
with the backslope inclination, the seismic acceleration, and the wall height. Based on a
design acceleration coefficient of about 0.30 and a wall height of "H" feet, we recommend
that these seismic loadings be modeled as the following uniform horizontal pressures for
various backslope angles:
14
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
Backslope
Angle
Level
3.OH:1 V
2.OH:1V
Active
At -Rest
Pressure
Pressure
4H psf
12H psf
6H psf
18H psf
8H psf
24H psf
zzalrerracon
Resisting Forces: The above-described loads applied to a wall can be resisted by a
combination of several other forces. These forces include passive pressure and base friction.
The following paragraphs present our recommended design values.
Passive Pressures: The soil located directly in front of a wall helps to resist both sliding and
overturning. This pressure acts over the entire embedded front of a wall, excluding the
upper 2 feet but including any shear keys, and it varies with the foreslope declination.
Assuming a level foreslope (as measured perpendicular to the wall face), we recommend
modeling the passive pressure as a triangular distribution equivalent to fluid weights of 300
pcf for static conditions and 400 pcf for transient conditions. These values incorporate static
and transient safety factors of at least 1.5 and 1.1, respectively.
Base Friction: The soil/concrete interface friction along the bottom of a wall footing can be
combined with the appropriate passive pressure to resist sliding. This force acts over the
entire basal surface of a footing. Assuming the footing concrete is cast directly on the soil
subgrade, we recommend using an allowable base friction coefficient of 0.4 for both static
and transient conditions. This single value incorporates static and transient safety factors of
at least 1.5 and 1.1, respectively.
15
Shell Valley Access Roadway
Edmonds, Washington
B1085007
May 16, 2008
CLOSURE
zZAlrerracon
The conclusions and recommendations presented in this report are based, in large part, on our
subsurface explorations accomplished for the project. It should be remembered that the
number, locations, and depths of these explorations were completed within the constraints of
budget, schedule, and site access. We wish to further emphasize that our explorations reveal
subsurface conditions only at discrete locations across the site; subsurface conditions in other
areas could vary considerably, but the nature and extent of any such variations would likely not
become evident until additional explorations are performed or construction activities have
begun. If significant variations are observed at that time, we may need to modify our
conclusions and recommendations to reflect the actual conditions.
We appreciate the opportunity to have been of service on this project and would be pleased to
discuss the contents of this report or other aspects of this project with you at your convenience.
Please call if you have any questions or need additional information.
Sincerely,
zzAlrerracon
ames M. Brisbine, P.E., L.G.
ssociate Engineer
Geotechnical Services Group
FIGURES
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GEOGRID OUTER WRAP
TOPSOIL INFILL
0 0
6' MIN,
BEARING BLANKET
24" MIN.
A
D A
77-77,77
SEPARATION ----/
FABRIC (AS NEEDED) OPTION 2: REINFORCED EDGE
EMBANKMENT
FILL
SEPARATION - -/
FABRIC (AS NEEDED)
2" MIN.
GABION
BASKET (3'x3')
12" MIN.
BEARING BLANKET ',-
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OPTION 3: GABION WALL
24" MIN.
Zipper Zeman Assocjiatei, Iijc.
Project No. 81085007
Shell Valley Access Roadway
Geotechnical and Environmental Consulting
Date: April, 2008
Edmonds, Washington
18905 33rd Avenue West, Suite 117
Drawn by: J. Duncan
FIGURE 4: EMBANKMENT EDGE
Lynnwood. Washington 98036
Scale: As Shown
DIAGRAMS
fele: (425) 771-3304 Fax: (425) 771-3549
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FIELD EXPLORATION
PROCEDURES, GENERAL NOTES, AND LOGS
B10850U7
FIELD EXPLORATION PROCEDURES
The following paragraphs describe our procedures associated with the on-site subsurface
explorations and field tests that we conducted for this project. Interpretive stratigraphic logs of
our explorations are enclosed in this appendix.
&tiger Boring Procedures
Our exploratory borings were advanced with a hollow -stem auger, using a track -mounted drill rig
operated by an independent drilling firm (Boretec, Inc.) working under subcontract to ZZA. A
geotechnical specialist from our firm continuously observed the borings, logged the subsurface
conditions, and collected representative soil samples. All samples were stored in watertight
containers and later transported to our laboratory for further visual examination and/or testing.
After each boring was completed, the borehole was backfilled with a mixture of bentonite chips
and soil cuttings, and the surface was patched with asphalt or concrete (where appropriate).
Throughout the drilling operation, soil samples were obtained at 2'/2- or 5 -foot depth intervals by
means of the Standard Penetration Test (SPT) per ASTM: D-1586. This testing and sampling
procedure consists of driving a standard 2 -inch -diameter steel split -spoon sampler 18 inches
into the soil with a 140 -pound hammer free -falling 30 inches. The number of blows required to
drive the sampler through each 6 -inch interval is counted, and the total number of blows struck
during the final 12 inches is recorded as the Standard Penetration Resistance (often called the
"SPT blow count" or "N value"). If a total of 50 blows are struck within any 6 -inch interval, the
driving is stopped and the blow count is recorded as 50 blows for the actual penetration
distance. The resulting Standard Penetration Resistance values indicate the relative density of
granular soils and the relative consistency of cohesive soils.
Each enclosed Boring Log describes the vertical sequence of soils and other materials
encountered in the respective borehole, based primarily on our field classifications and
supported by our subsequent laboratory examination and/or testing. Where a soil contact was
observed to be gradational within the sampler, our logs indicate the average contact depth;
where a soil type changed between two sample intervals, we show an inferred contact depth.
Our logs also graphically indicate the blow count, sample type, sample number, and
approximate depth of each soil sample obtained from the borings, as well as any laboratory
tests performed on these soil samples. If any groundwater was encountered in a borehole, the
approximate groundwater depth is depicted on the boring log. Groundwater depth estimates
are typically based on the moisture content of soil samples, the wetted height on the drilling
rods, and the water level measured in the borehole after the auger has been extracted.
B1085W7
GENERAL NOTES
DRILLING & SAMPLING SYMBOLS:
< 15
Boulders
SS:
Split Spoon - 1 ,r`8" I.D., 2" O.D.. unless otherwise noted
HS
Hollow Stem Auger
ST
Thin -'Platted Tube - 2" 0 D, unless otherwise noted
PA
Power Auger
RS:
Ring Sampler - 2.42" 1 D , 3" O -D., unless otherwise noted
HA:
Hand Auger
DB
Diamond Bd Coring - 4'% N, B
RB:
Rock Bit
BS:
Bulk Sample or Auger Sample
VIJB
'Nash Boring or Mud Rotary
The number of blows required to advance a standard 2 -inch 0-D. spilt -spoon sampler (SS) the last 12 inches of the total 1134nch
penetration with a 140 -pound hammer falling 30 inches is considered the Standard Penetration` or "N•value'
WATER LEVEL MEASUREMENT SYMBOLS:
WL Water Level WS While Sampling WE Not Encountered
WCI Wet Cave in WD: While Drilling
DCi Dry Cave in BCR: Before Casing Removal
AS: After Boring AGR: After Casing Removal
Water levels Indicated on the boring logs are the levels measured in the borrlgs at the times indicated Groundwater levels at other
Umes and other locations across the site could vary. In pervious sots, the Indtcateci levels may resect the location of groundwater. In
tow permeability soils the accurate determination of groundwater levels inlay not be possible with only short -terra observations.
DESCRIPTIVE SOIL CLASSIFICATION: Soil classification is based on the Unified Classification System. Coarse Grained Soils have
more than 50% of their dry weight retained on a 4200 sieve; their principal descriptors are boulders, cobbles. gravel or sand. Fine
Grained Soils have less than 50% of their dry weignt retained on a 1200 sieve, they are principally described as days if they are plastic,
and silts if they are slightly piastic or non -plastic Major constituents (nay be added as modifiers and minor constituents may be added
according to the relative proportions based on grain size In addition to gradation, coarse-grained soils are defined on the basis of their
in-place relative density and fine-grained soils on the basis of their consistency_
CONSISTENCY OF FINE-GRAINED SOILS RELATIVE DENSITY OF COARSE-GRAINED SOILS
Stand r
Unconfined Penetration or Standard Penetration
Compressive N -value (SS) or N -value (SS)
Strength. Chu, ast BlowslFt. JalowslFt,
Consistency Relative Densitv
500 a2 very Soft 0-3 Very Lame
500 — 1.000 2-3 Soft 4-9 Loose
1.001 — 2.000 4-6 Medium Stiff 10-29 Medium Dense
2.001 — 4.000 7-12 Stiff 30-49 Dense
4,.001 — 8 000 13-213 Very Stiff 60+ Very Dense
8,000+ 26+ Hard
RELATIVE PROPORTIONS OF SAND AND GRAVEL GRAIN SIZE TERMINOLOGY
Descriptive Term is) of other Percent of Major Component
constituents DN Weight of Sample Particle Size
Trace
< 15
Boulders
Over 12 in. (300mm)
with
I �F -- 29
Cobbles
12 in to 3 in (300mm to 75 mm)
Modifier
-30
Gravel
3 in. to #4 sieve (75mm to 4 75 mm)
Sand is l to #2ily sieve (4.75mm to 0 075mm)
RELATIVE PROPORTIONS OF FINES
SII; or Clay
Passing 1#2^,70 Sieve (0 075mrn)
Descriptive Terms) of other
Percent of
PLASTICITY
DESCRIPTION
constituents
Dry Weight
Term
Pjasttcity Index
Trace
s 5
Non -plastic
0
With
5-12
Low
1-10
Modifiers
> 12
Medium
11-30
High
30+
itICJ■'"flr�ii`'
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131085007
LOG OF BORING NO. B-1
Pa2e 1 of 2
CLIENT
Perteet, Inc.
SITE
PROJECT
Edmonds, WA
Shell Valley Access Roadway
SAMPLES
TESTS
DESCRIPTION
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.33—t GRASS SURFACE with silt, sand, gravel t-36
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FINE TO COARSE SAND with gravel and
some silt, grayish brown to brown, medium
dense, moist (Fill)
GSA
SM
S-1
P
8
12
12
4--------------------------357
SILTY FINE TO MEDIUM SAND with
gravel and occasional cobbles, brown,
loose to dense, moist (Fill)
5
SM
S-2
PT
8
36
10
SM
S-3
SPI
6
8
i5
SM
S-4
P
8
22
0
c�
o..;:.
17 ---------------- 344
oSILTY
GRAVEL with sand, brown and
orange mottled, dense to very dense, moist Q
(Advance Outwash)
O c
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m
W
Continued Next Pae
20
J
d The
stratification lines represent the approximate boundary lines
between
soil and rock types. in-situ, the transition may be gradual.
N WATER
LEVEL OBSERVATIONS, It
18 3/14/08 IT :i«. ka
torr
n
BORING
STARTED
3-14-08
WL
BORING
COMPLETED
3-14-08
WL
Z — --
RIG
Volvo
E55
CO.
Boretec
m WL
LOGGED
Scott
JOB
#
B1085007
LOG OF BORING NO. B-1
Page 2 of 2
CLIENT
Perteet, Inc.
SITE
PROJECT
Edmonds, WA
Shell Valley Access Roadway
SAMPLES
TESTS
0
o
DESCRIPTION
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SM
S-5
SPT
10
55
orange mottled, dense to very dense, moist
p
(Advance Outwash)
0
O
a
D
°
25
GP
S-6
SPT1
0
150/5"
°
GM
0
0
0
a
0
0
0
30.5 330.5
30
GP
S-7
P
0
50/5"
GM
Boring completed at -30.5 feet on 3/14/08
Q
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O
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0
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it
0
m
r
0
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stratification lines represent the approximate boundary lines
> between
soil and rock types: in-situ, the transition may be gradual.
w
N WATER
LEVEL OBSERVATIONS, ft
18 3/14/08 1 "Z ti�M,
BORING
STARTED
3-14-08
WL
COMPLETED
3-14-08
WL
w
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aconBORING
RIG
Volvo
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LOGGED
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# B1085007
LOG OF BORING NO. B-2
Page 1 of 2
CLIENT
Perteet, Inc.
SITE
PROJECT
Edmonds, WA
Shell Valle Access Roadway
SAMPLES
TESTS
DESCRIPTION
M
Z i
_
CL
3f(n
w
m
>
Z
ALU
Z
=)
ZZ
t—
w
(0
N
n
w
n
O
w
w F—
d0
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Approx. Surface Elev.: 361 ft
o
z
aQ
X
z�
.33—t GRASS SURFACE with silt, sand, gravel36(14
\and roots, brown, loose, moist
SILTY FINE TO COARSE SAND with
gravel, brown, medium dense, moist (Fill)
SM
S-1
SPT
8
21
4 357
---------------
— — — —
SILTY FINE TO MEDIUM SAND with
gravel and occasional cobbles, brown to
orange brown, loose, moist (Fill)
5
GSA
SM
S-2
PT
8
9
13
to
SM
S-3
P
0
6
14.5-----------------------346.5
-
FINE SAND with silt and a trace of gravel
light brown, medium dense to very dense,
15—SM
GSA
S-4
Pj
12
15
5
moist (Advance Outwash)
O
Q ,
C
FW -
'a
h
O
J
20341
--------
Continued Next Page
20
W
J
The
stratification lines represent the approximate boundary lines
J J between
soil and rock types: in-situ, the transition may be gradual.
W
(30: WATER
LEVEL OBSERVATIONS, ft
28 77� �4/08 -1-
BORING
STARTED
3-14-08
WL
BORING
COMPLETED
3-14-08
$ WL
k
RIG
Volvo
E55
CO.
Boretec
& WL
LOGGED
Scott
JOB
#
B1085007
LOG OF BORING NO. B-2
Page 2 of 2
CLIENT
Perteet, Inc.
SITE
PROJECT
Edmonds, WA
Shell Valley Access Roadway
SAMPLES
TESTS
DESCRIPTION
m
>-
W o
U
a.N
ED
w
Zr
Z
a
W
O
wE_
Ow
O
o
z
X vaim
"y 00
0 a
5W
SILTY GRAVEL with sand and occasional
GP
S-5
Plj
0
50/4"
°
cobbles, grayish brown, very dense, moist
GM
"
(Advance Outwash)
°
0
0
O
24 ------------------------ 337
SILTY FINE TO MEDIUM SAND with a
trace of gravel, light brown, dense, moist
(Advance Outwash)
25
SP
S-6
SPT
16
48
26.5______________ ____ ____3_34.5
"
FINE TO MEDIUM SAND with some silt
27"5 and a trace of gravel, light brown, dense, 333.5
— --I moist (Advance Outwash) _ _ _ _ _ _ — —
------------ —
SILTY FINE TO COARSE SAND,brown -
and orange mottled, very dense, wet
(Advance Outwash)
30
SM
S-7
SPT
2
50/5"
33 328
—
SILTY FINE TO COARSE SAND with
gravel, brown, very dense, moist (Advance
Outwash)
Q
35
SM
S-8
E;PT
4
50/5"
8
'.
36 325
z
Boring completed at -36 feet on 3/14/08
'a
(t9
O
J
z
2
K
O
m
J
The
stratification lines represent the approximate boundary lines
between
J
soil and rock types. in-situ, the transition may be gradual.
w
WATER
LEVEL OBSERVATIONS, ft
s 28 3/14/08 �N+� w;
--�" _
fir%
BORING
STARTED
3-14-08
WL
BORING
COMPLETED
3-14-08
WL
RIG
Volvo
E55
CO.
Boretec
o WL
m
LOGGED
Scott
I JOB
#
131085007
LOG OF BORING NO. B-3
Page 1 of 1
CLIENT
Perteet, Inc,
SITE
PROJECT
Edmonds, WA
Shell Valley Access Roadway
SAMPLES
TESTS
o
DESCRIPTION
m
w a
z
U
a
=
w
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F
a:w
H
Z
zZ
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°
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w
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a�¢o
w F-
w
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o
z
o:
U
0 a
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'= _q
o.5 SANDY SILT with organic matter and 348.5
_1 ome gravel, brown, loose, wet (Colluvium)_
SILTY FINE TO MEDIUM SAND with
some gravel and organic matter, brown
and orange mottled, loose, moist
(Colluvium)
SM
S-1
SPT
8
7
._4346
345
FINE TSE O COARSAND with silt and
some gravel, brown and orange mottled,
medium dense, moist (Advance Outwash)
5
SP
S-2
SPI
6
13
SM
grades to grayish brown and some gravel
SP
S-3
SPT
10
23
SM
grades to dense
10
SP
S-4
P
12
45
SM
11 5 337.5
Boring completed at -11.5 feet on 3114108
0
0
a
'a
t�
0
J
z
0
m
J
a The
stratification lines represent the approximate boundary lines
jbetween
soil and rock types in-situ, the transition may be gradual.
w
N WATER
LEVEL OBSERVATIONS, ft
V 112 1,,,,
BORING
STARTED
3-14-08
WL
BORING
COMPLETED
3-14-08
WIL
s'
rr
RIG
Volvo
E55
CO.
Boretec
W
o WL
LOGGED
Scott
JOB
#
B1085007
LOG OF BORING NO. B-4
Page 1 of 1
CLIENT
Perteet, Inc.
SITE.
PROJECT
Edmonds, WA
Shell Valley Access Roadway
SAMPLES
TESTS
DESCRIPTION
m
>
°w
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x
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zcn
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u_
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a
v
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w
o
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=)z
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IL
m
¢O
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❑ a
ZF
M
SANDY SILT with organic matter and 341_5
come gravel, brown, soft, wet (Colluvium) i^
SANDY SILT with some organic matter
and a trace of gravel, brown, stiff, wet
(Colluvium)
ML
S-1
6
16
4------------------------- 338
�Pj
SILTY FINE TO MEDIUM SAND, brown
and orange mottled, loose, moist (Fill)
5
SM
S-2
E3PI
1
8
SM
S-3
3PI
2
5
..`-
10_5v-----------------------331.5
10
SM
S-4
P7
6
17
SILTY FINE TO MEDIUM SAND, brown
and orange mottled, medium dense, moist
(Advance Outwash)
grades to grayish brown and orange
mottled and dense
m
15
SMS-5
P
10
48
o
16.5 325.5
W
Boring completed at -16.5 feet on 3114108
a'
c�
0
z
0
0
m
J
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stratification lines represent the approximate boundary lines
between
J
soil and rock types: in-situ, the transition may be gradual,
LL7
WATER
LEVEL OBSERVATIONS, ft
s
err
BORING
STARTED
3-14-08
WL
BORING
COMPLETED
3-1408
WL
RIG
Volvo E55
CO.
Boretec
W
m WL
LOGGED
Scott
JOB
#
B1085007
APPENDIX B
LABORATORY TESTING
PROCEDURES, CLASSIFICATIONS, AND RESULTS
LABORATORY TESTING PROCEDURES
The following paragraphs describe our procedures associated with the laboratory tests that we
conducted for this project. Our test results are enclosed in this appendix and/or are shown on
the exploration logs contained in Appendix A. As part of our testing program, the samples were
examined in our laboratory and classified in accordance with the attached Genera! Notes and
the Unified Soil Classification System (USCS), based on the texture and plasticity of the soil.
The estimated group symbols for native samples using this system are shown on our boring
logs. A brief description of the USCS is included with this appendix.
Visual Classification Procedures
Visual soil classifications were conducted on all samples in the field and on selected samples in
our laboratory. All soils were classified in general accordance with the United Soil Classification
System, which includes color, relative moisture content, primary soil type (based on grain size),
and any accessory soil types. The resulting soil classifications are presented on the exploration
logs contained in Appendix A.
Moisture Content Determination Procedures
Moisture content determinations were performed on representative samples to aid in
identification and correlation of soil types, All determinations were made in general accordance
with ASTM: D-2216. The results of these tests are shown on the exploration logs contained in
Appendix A.
Grain Size Analysis Procedures
A grain size analysis indicates the range of soil particle diameters included in a particular
sample. Grain size analyses were performed on representative samples in general accordance
with ASTM: D-422. The results of these tests are presented on the enclosed grain -size
distribution graphs and were used in soil classifications shown on the exploration logs contained
in Appendix A.
B1095007
UNIFIED SOIL CLASSIFICATION SYSTEM
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests*
Soil Classification
Group
Symbol
Grotp Name"
Coarse Gralix-d Solis
Gravers
Clean L7rave•rs
Cu _ 4 and 1 _ G^-, 3'
GN:
•,NeiiSradeo grave'
Moe than 5G°6 retained
More than 5C% of coarse
fracfon reta--lied on
Less than 5%fines
Cd . s andtor t Cc 3F
C,P
Feat y graded graver
on No 200 sieve
No 4 sieve
Gravels with FIneS More Fines classify as M._ of MH
GNI
S!Itygrave.`° "
than 12`fa fires
Funs classfy, as CL or Cfi
GC
Clayey gravel,
Sans
CA'an Sands
Cu_ 5 and t _ C -C:,?`
SW
Well -graded sand'
5clb or store of coarse
Less than Sac ffnr'
fraction passes
Cv e. a,~dror 1 Cr_ 3r
SP
Poorly graded sand
No, 4 sleve
Sands aith Fines
Fines classify as ML or fvlH
SM
S!Itt'sand-"
More than '2% firs=
Fines Classihr as CL or CH
SC.
riayey Sart""'
Fhte-Giaioea Soils
Silts ar5d Craye
lragarfc
FI 7 and pints on o; alwve'A' line
Ci-
Lean clay,
50% or mon pisses the
Liqurc limit less than 50
NO. 2'x sb ve
PI 4 or k!rs tie rw "A' Uns'
P
t.Y
S#t ' "
arovi.
LIgUdILntl- o'rendried
OrganicCklyr,4 "
C 75
OIL
Liquid incl - not dned
Cxgan:c 5!ltK: "
34ts and Clays
irorga^i c
FI plots W cr above 'A' -ine
CF
Rr car""
Liqud Out 50 or Pian
PI plots irelo v'A" jlns
4',H
Elas Vc Silt"'
rrganlC
Lxiurd Unit - O'rr:n dried
Organic Clay 0
075
CN -
Laud Jnyt - not dned
::rgatic sit`
Highly organic s'Als
Primarily
organic mallei• dark in
color and (,-gardc odor
FT
Per.
"Based on the material passing die 3 -in 1n
75-xm) sieve
31f field sample contained cobbles or boulders, or both, add "with cobbles
or boulders, or both' to group name.
Gravels with 5 to 12% fines require dual symbols- GW -GM weU-graded
gravei with silt. GYN -GC well -graded gravel vxth clay_ GP -G%-1 poorly
graded gravel with silt, GP -GC poorly graded gravel *nth clay
`Sa icls with 5 to 12% fines requre dual symbols- SW -Su weal -graded
sen •wrth silt SW -SC well -graded sand with clay, SP SM poorly graded
sand with slit: SP -SC poorly graded sand will, clay
=Cu = D5y'D,r Cc= (D- `
DcX De
if soil contains _ 16% sand, add -with sand" to group name
"If tines Cissify as CL -RAL use dual symbol GC-Gfv1, or K -SNI.
fr)
For classffloation of lino -grained
solis and fine --grained inaction
Of coarse•gralnoo soils
rr�tix,n" of 'A - 8ne
lroirtonisF ui ?1�4 ;v il.-.15 v
X 40 1hrnP!_O:3ILI-i10)
n twahcr. of •U' nine %
Z VarGcnf al lt.= i6 to Y!=i /
T
30 IMi' PisO it ill. -Al
-If fines are organic. add -with organic ttnes to group name
If soil contains 15°r: gravel, add "with gravel" to group name
if Atferberg limits plot in shaded area, sal is a CL -ML, silty clay
if sod contains 15 to 29% plus No. 200 add -with sandor `istth
gravel,' whicheear is predominant
1f soil contains _ 30% plus No 200 predom mir tty sand, :add
sandy" to group name
"If soil contains', 30% pW No. 2W predomi iantly gravel, add
"gavel:y' to group new
"Pi ; an plots on or above A" line
'Pk, 4 or plots below'A" fne
°Pi plots on or abave'A" line.
"PI plots below: A' line.
` fw'
cn 20
�U
EL MH o^ OH
to
4 Ift or OL
dJ i
0 10 t5 20 30 »ti Y., vci Al
LIQUID LIMIT (LL)
61085007
1:.. :tt tyJ 110
100
90
2 80
0
W
70
Im
W 6C
z
Il.
Z 50
W
U
W 40
CL
3C
2C
1C
C
1000.000
GRAIN SIZE ANALYSIS Test Results Summary ASTM D 422
100.000 10.000 1.000 0100 0.010 0.001
PARTICLE SIZE IN MILLIMETERS
Comments.
Exploration
Sample
Coarse
Fine
Coarse
Medium
Fine
Sill
Clay
BOULDERS
COBBLES
GRAVEL
SAND
FINE GRAINED
Comments.
Exploration
Sample
Depth (feet)
Moisture (%)
Fines (%)
Description
B-1
S-1
2.5-4
12
97
SAND with gravel and
silt
JOB NO 81085007 PROJECT NAME:
DATE OF TESTING. 3I21I2008 Shell Valley ACCESS
Geoleohnical and Environmental Consulting Roadway
10C
9C
H
= 8C
C9
W
7C
i'
m
W 6C
Z
z 5C
W
U
W 4C
CL
3C
2(
1(
1000.000
GRAIN SIZE ANALYSIS Test Results Summary ASTM D 422
100.000 10.000 1.000 0.100 0.010 0.001
PARTICLE SIZE IN MILLIMETERS
Comments:
Exploration
I
Coarse
Fine
Coarse
Medtum
Fine
Silt
Clay
BOULDERS
COBBLES
GRAVEL
SAND
FINE GRAINED
Comments:
Exploration
Sample
Depth (feet)
Moisture (%)
Fines (%)
Description
B-2
S-2
5-6.5
13
24.8
silty SAND with gravel
JOB NO: 81085007 PROJECT NAME-
Wm-
A- �'�° n DATE OF TESTING: 3/2112008 Shell Valley Access
Geoteohnical and Environmental Consulting Roadway
1010
z
BC
0
W
7C
d1
W 6C
Z
W
Z 5C
W
U
W 4C
a
3C
2C
1C
C
1000.000
GRAIN SIZE ANALYSIS Test Results Summary ASTM D 422
100.000 10.000 1.000 0.100 0.010 0.001
PARTICLE SIZE IN MILLIMETERS
BOULDERS
COBBLES
Coarse
Fine
Coarse
Medium
Fine
Siff
Clay
GRAVEL
SAND
FINE GRAINED
Comments:
Exploration
Sample
Depth (feet)
Moisture (%)
Fines (%)
Description
B-2
S-4
15-16.5
5
5.7
FINE SAND with silt
and trace gravel
c:•
JOB NO: 81685007 PROJECT NAME.
eag
DATE OF TESTING 3721/2008 Shell Valley Access
Geotechnical and Environmental Consulting Roadway
Wan -Yee Kuo
From:
Brisbine, James M Umbrisbine@terracon.com]
Sent:
Monday, June 01, 2009 5:18 PM
To:
Wan -Yee Kuo
Cc:
Darrell Smith
Subject:
RE: Edmonds Shell Valley -infiltration rate
Wan -Yee - In the third bullet, I think you meant Station 12+75. In the fourth bullet, replace "required" with "expected."
Otherwise, your summary is accurate.
1NIN
James M. Brisbine, P.E.
Senior Project Engineer I Geotechnical
ZZA-Terracon
14405 SE 36th Street, Suite 210 1 Bellevue, WA 98006
P 425-746-1889 1 F 425-746-1296 1 M 425-218-4614
imbrisbine(a)-terracon.com I www.terracon.com
From: Wan -Yee Kuo [mailto:wkuo@perteet.com]
Sent: Monday, June 01, 2009 5:08 PM
To: Brisbine, James M
Cc: Darrell Smith
Subject: RE: Edmonds Shell Valley -infiltration rate
Jim,
It was good talking to you. Thanks for getting back to me promptly.
Per our discussion, I understand that the following criteria would apply to the Porous Concrete roadway.
• Amended soil layer with 92% compaction will conservatively yield an infiltration rate of 1.4" per hour.
• The existing soil under the roadway is estimated at 1" per hour infiltration rate.
• From station 11+50 to 112+75 (Intersection with Main street)), the project will require the removal of minimum
top 12" soil to allow for infiltration. The over excavated area shall be filled with Gravel Borrow.
• From station 10+00 to 11+50, over excavation is not required.
• You recommend that the project should require a Geotech to be on-site in case more over -excavation is needed
during construction.
Please let me know if you have any concerns or I have missed something.
Thanks.
Wan -Yee
From: Brisbine, James M [mailto:jmbrisbine@terracon.com]
Sent: Monday, June 01, 2009 3:37 PM
To: Wan -Yee Kuo
Cc: Darrell Smith
Subject: RE: Edmonds Shell Valley -infiltration rate
Wan -Yee -
The amended soil you described to me back in April is similar to our B -2/S-4 soil sample, which yielded an ultimate rate of
44 inches per hour. When used as roadway subgrade, it becomes more difficult to estimate a rate for it, because there are
limitations on the vertical extent of amended soil. Plus, the soil will need to be compacted to support traffic loads, rather
than left in a more porous condition. WSDOT suggests reducing the rate by about 10 to account for compaction.
By combining this reduction with a safety factor of 20, we're left with 44/(10+20) =1.4 inches per hour. I'd be extra
conservative on using that value, however.
Jim
James M. Brisbine, P.E.
Senior Project Engineer I Geotechnical
ZZA-Terracon
14405 SE 36th Street, Suite 210 1 Bellevue, WA 98006
P 425-746-1889 1 F 425-746-1296 1 M 425-218-4614
imbrisbine@terracon.com I www.terracon.com
From: Wan -Yee Kuo [mailto:wkuo@perteet.com]
Sent: Monday, June 01, 2009 3:10 PM
To: Brisbine, James M
Cc: Darrell Smith
Subject: RE: Edmonds Shell Valley -infiltration rate
Thanks, Jim. What about the roadway? Do you have an estimate for that?
From: Brisbine, James M [mailto:jmbrisbine@terracon.com]
Sent: Monday, June 01, 2009 3:08 PM
To: Wan -Yee Kuo
Cc: Darrell Smith
Subject: RE: Edmonds Shell Valley -infiltration rate
Hello Wan -Yee,
I've finished my calculations of infiltration rates based on our previous three grain -size test results, using the WSDOT
HRM method (4-5.2.1).
For the gallery with a bottom elevation at 346 feet, I calculated an ultimate infiltration rate of 45 inches per hour.
For the trenches, with a bottom elevation at 352 feet, I calculated an ultimate infiltration rate of 24 inches per hour.
When we perform field infiltration testing, we typically apply a safety factor of 10 to the ultimate value. Since we did not
perform any field testing for this study, I recommend applying a minimum safety factor of 20. This would result in the
following maximum design rates:
Gallery: 2.25 inches per hour
Trenches: 1.2 inches per hour.
Good luck in your meeting tomorrow!
RFIT
James M. Brisbine, P.E.
Senior Project Engineer I Geotechnical
ZZA-Terracon
14405 SE 36th Street, Suite 210 1 Bellevue, WA 98006
P 425-746-1889 1 F 425-746-1296 1 M 425-218-4614
imbrisbine(a)terracon.com I www.terracon.com
From: Wan -Yee Kuo [mailto:wkuo@perteet.com]
Sent: Monday, June 01, 2009 10:34 AM
To: Brisbine, James M
Subject: RE: Edmonds Shell Valley -infiltration rate
Hi, Jim. Hope you had a good weekend.
I am checking in to see if you have any questions for me.
I also would like to know when you will have an estimate today. I have a meeting with the client tomorrow afternoon
so I would like to confirm the recommended design infiltration rate as soon as possible. If the rate is less than 1" per
hour, I would need to update my design and report.
Thanks. Let me know what you think.
Wan-yee
From: Wan -Yee Kuo
Sent: Friday, May 29, 2009 11:29 AM
To: 'Brisbine, James M'
Cc: Darrell Smith; Dean Franz
Subject: Edmonds Shell Valley -infiltration rate
Jim,
Per our discussion, please follow the infiltration rate estimate method outlined in the WSDOT Highway Runoff Manual
(2008). The process is outlined under Section 4-5.2.1
The bottom of the infiltration gallery will be at elevation 346. The roof infiltration trench bottom is about elevation 352.
The bottom of the amended soil will follow the roadway elevation. The porous concrete is designed to be 8" thick, on
top of an 8 inch thick modified crushed surfacing base course ( reduce to only 1-2% fines)as we discussed and there will
be an 1.5' amended soil layer.
You have the plan drawing and the roadway section and I am also attaching a roadway profile for your reference. I hand
sketched in the pavement design layers.
We are interested in your recommended design infiltration rates and hopefully by Monday. Please call me at my cell
phone 206-992-0987 if you have any questions today. You can call me at 425-322-0278 ( my direct line at work) on
Monday if you need to talk to me.
Thank you.
Wan -Yee
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