GEO Tech Report.pdfff q I-IWA.GE0S(JEI14C'I,,S INC
September 18, 2014
HWA Project No. 2013-054-21
City of Edmonds
700 Main Street
Edmonds, Washington 98020
Attention: Carrie Hite
Subject: FINAL GEOTEctINICAL INVESTIGATION REPORT
City Park Play and Spray Area Revitalization
Edmonds, Washington
Dear Carrie,
This report summarizes the results of our geotecl-mical investigation for the revitalization project
of the proposed Play and Spray Area at City Park in Edmonds, Washington. The purpose of our
investigation was to characterize soil and ground water conditions in the vicinity of the proposed
improvements, and provide geotechnical recommendations for design and construction of an
underground water storage tank, as well as general earthwork reconn-nendations for the spray
area.
Our work was conducted in general accordance with the scope of work presented in our April 4,
2013 proposal and addenda to our scope dated October 17, 2013 and May 7, 2014. Our scope of
work included site reconnaissance, subsurface explorations, laboratory testing of soils, and
engineering analyses to develop geotechnical recommendations for design and construction of
the Play and Spray Area. Recommendations presented in this report include soil bearing
capacity, buoyancy mitigation for the underground structures, initigation of shallow ground
water seepage in the play area, general earthwork, and pavement subgrade recommendations.
The purpose of the additional scopes of work was to characterize soil and ground water
conditions that would be encountered in excavations for the stormwater detention system, as well
as for the proposed spray water storage tank to evaluate whether a shallower excavation than
initially planned would be advantageous.
SITE AND PROJECT DESCRIPTION
The existing park is at the toe of the overall west -facing slope in Edrnonds. This site is also just
upslopc and to the east of the near -tidal marsh. along SR 104, as shown ori Figure 1.
The park consists of a ball field, at the eastern uPslopc portion along Third
A31:? 30th Di ive SE
Avenue; the existing playground with adjacent picnic shelters and restroom Suite 110
building; and a parking lot, at the western downslope Md. The existing Bothell, NVA 9802 IJOI 0
Tel: 425.774.0106
Fax: 42'074.2714
mm.11%vageo'com
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Attention: Carrie Hite
Subject: FINAL GEOTEctINICAL INVESTIGATION REPORT
City Park Play and Spray Area Revitalization
Edmonds, Washington
Dear Carrie,
This report summarizes the results of our geotecl-mical investigation for the revitalization project
of the proposed Play and Spray Area at City Park in Edmonds, Washington. The purpose of our
investigation was to characterize soil and ground water conditions in the vicinity of the proposed
improvements, and provide geotechnical recommendations for design and construction of an
underground water storage tank, as well as general earthwork reconn-nendations for the spray
area.
Our work was conducted in general accordance with the scope of work presented in our April 4,
2013 proposal and addenda to our scope dated October 17, 2013 and May 7, 2014. Our scope of
work included site reconnaissance, subsurface explorations, laboratory testing of soils, and
engineering analyses to develop geotechnical recommendations for design and construction of
the Play and Spray Area. Recommendations presented in this report include soil bearing
capacity, buoyancy mitigation for the underground structures, initigation of shallow ground
water seepage in the play area, general earthwork, and pavement subgrade recommendations.
The purpose of the additional scopes of work was to characterize soil and ground water
conditions that would be encountered in excavations for the stormwater detention system, as well
as for the proposed spray water storage tank to evaluate whether a shallower excavation than
initially planned would be advantageous.
SITE AND PROJECT DESCRIPTION
The existing park is at the toe of the overall west -facing slope in Edrnonds. This site is also just
upslopc and to the east of the near -tidal marsh. along SR 104, as shown ori Figure 1.
The park consists of a ball field, at the eastern uPslopc portion along Third
A31:? 30th Di ive SE
Avenue; the existing playground with adjacent picnic shelters and restroom Suite 110
building; and a parking lot, at the western downslope Md. The existing Bothell, NVA 9802 IJOI 0
Tel: 425.774.0106
Fax: 42'074.2714
mm.11%vageo'com
September 18, 2014
HWA Project No. 2013-054-21
playground consists of two levels separated by a paved path and a short retaining wall. The
upper play area is separated from the grassy slope above by two short concrete retaining walls.
We understand that the City of Edmonds plans to revitalize the existing playground by
constructing a Play and Spray Area, with the spray area in the existing upper playground and a
new play area in the existing lower playground. The proposed improvements consist of a spray -
play area system, new play equipment, an expansion of the playground area toward the south,
water and sanitary sewer lines, and a collection and storage system for runoff from the spray area
for recirculation. The latter will include installation of an underground 5,000 gallon, 6 -foot
diameter, 25 -foot long cylindrical plastic storage tank for storage of runoff. The storage tank
will be located on the north side of the existing playground and tied to a concrete slab to be
poured beneath it, as a dead weight necessary to combat uplift buoyancy forces. We understand
the excavation for the tank will be up to approximately 10 feet deep below the existing ground
level.
A stormwater detention system is also proposed and will be located along the downslope edge of
the existing playground. The detention system will likely consist of two 4'/2- to 5 -foot diameter
pipes, approximately 60 feet long, with associated manholes and piping. Excavations for the
vaults are anticipated to be up to approximately 10 feet below existing ground surface.
Per conversations with Rich Lindsay, Park Maintenance Manager, we understand that extensive
ground water seepage was encountered during construction of the playground in the 1980's.
Rich stated that seepage was observed in the cut made for the two upper retaining walls, where
the total cut was of the order of 4 to 5 feet. A perimeter footing drain was installed
approximately 4 feet below ground surface on the uphill side of the upper wall. In addition, Mr.
Lindsay indicated that while digging to place the existing playground equipment posts, seepage
was encountered that rose to the ground surface. In response, a series of "finger" drains up to
3 feet deep were placed in most of the upper play area.
General geologic information for the site was obtained from the publication Composite Geologic
Map of the Sno-King Area (Booth et al, 2004). The map indicates that the surficial geology of
the site consists of pre -Fraser Glaciation deposits; which consist of non -glacial deposits of silt
and sand (from lake and river deposits), which were subsequently overridden by glacial ice
during the Fraser Glaciation and thus overconsolidated to a very compact and very dense
condition.
2013-054 FR 2 HWA GEOSCIENCES INC.
September 18, 2014
HWA Project No. 2013-054-21
FIELD ExPLORATIONS
The field exploration program included review of available geologic data from the vicinity,
performing a surface reconnaissance using a 3 -foot long, %2 -inch diameter, steel soil probe,
drilling two boreholes to depths of 11.5 and 21 feet, installing piezometers in the two boreholes,
and digging two handholes to refusal at depths just over 2 feet. The need for additional
explorations for the stormwater system and tank was identified by the initial work and
subsequent design revisions by SiteWorkShop. The additional explorations consisted of six test
pits excavated to depths of 6.5 to 13 feet at the locations of the proposed stormwater detention
pipes and the underground storage tank, as well as in the proposed spray area, as shown on
Figure 2.
The two boreholes, designated BH -1 and BH -2, were drilled on September 23, 2013, with a
small rubber -tracked drill rig, using hollow -stem augers. The drilling was performed by Geologic
Drill Exploration, Inc. who was under subcontract to HWA. The two handholes, designated
HH -1 and HH -2, were excavated with a posthole digger and hand auger on October 10, 2013 to
evaluate subsurface conditions within the existing lower play area. The six test pits, designated
TP -1 and TP -2, were excavated with a backhoe and operator provided by the City on October 29,
2013 and May 12, 2014.
Soil samples from the handholes and test pits were collected at selected intervals. Soil samples
from the boreholes were collected at 2.5- to 5 -foot intervals using Standard Penetration Test
(SPT) methods in general accordance with ASTM D-1586. SPT sampling consisted of using a
2 -inch outside diameter, split -spoon sampler driven with a 140 -pound drop hammer using a rope
and cathead. During the test, a sample is obtained by driving the sampler 18 inches into the soil
with the hammer free -falling 30 inches per blow. The number of blows required for each
6 inches of penetration is recorded. The Standard Penetration Resistance ("N -value") of the soil
is calculated as the number of blows required for the final 12 inches of penetration. If a total of
50 blows is recorded within a single 6 -inch interval, the test is terminated, and the blow count is
recorded as 50 blows for the number of inches of actual penetration. This resistance, or N -value,
provides an indication of the relative density of granular soils and the relative consistency of
cohesive soils. Upon completion of drilling, a 1 -inch PLIC standpipe piezometer was installed in
each boring, with a flush -mounted steel monument. Ground water levels were subsequently
measured periodically (see Table 1 below).
Representative soil samples were taken to our laboratory for further examination. Pertinent
information including soil sample depths, stratigraphy, soil engineering characteristics, and
ground water occurrence was recorded and used to develop logs of the explorations. Summary
logs of the explorations and a legend to the terms and symbols are presented in Appendix A.
2013-054 FR 3 HWA GEOSCIENCES INC.
September 18, 2014
HWA Project No. 2013-054-21
The stratigraphic contacts shown on the individual logs represent the approximate boundaries
between soil types; actual transitions may be more gradual. Moreover, the soil and ground water
conditions depicted are only for the specific locations and dates reported and, therefore, are not
necessarily representative of other locations and times.
Laboratory tests were conducted on selected soil samples to characterize relevant engineering
properties of the on-site materials. The laboratory testing program was performed in general
accordance with appropriate ASTM Standards as outlined below. Figures B-1 and B-2 present a
summary of the material properties obtained from our testing program.
Moisture Content of Soil: The moisture content of selected soil samples (percent by dry mass)
was determined in accordance with ASTM D 2216. The results are shown at the sampled
intervals on the appropriate exploration logs.
Particle Size analysis of Soils: Selected samples were tested to determine the particle size
distribution of material in accordance with ASTM D422 (wet sieve or wet/hydrometer method).
The results are summarized on the attached Grain Size Distribution Reports, Figures B-3 and
B-4, which also provide information regarding the classification of the samples and the moisture
content at the time of testing.
Brief general descriptions of the soil units observed in our site explorations are presented below
in order of deposition, beginning with the most recently deposited. The exploration logs
presented in Appendix A provide more detail of subsurface conditions observed at specific
locations and depths. The soils encountered in the explorations are described below:
Fill — Fill was observed in each of our explorations performed at the site. Dense to very dense,
olive brown, silty, gravelly, sand was encountered in the upper 7 feet of borehole BH -1, near the
location of the proposed storage tank. Based on its density and unweathered coloration, in
juxtaposition to underlying soils of lower density and weathered coloration, the upper material in
BH -1 appears to be fill. Test pit TP -2, located about 30 feet north of BH -1, encountered only 21/2
feet of fill consisting of silty, gravelly sand, with organics. Test pit TP -1, excavated within the
proposed stormwater retention area, encountered 6 feet of fill, also consisted of silty, gravelly
sand, with abundant organics including partly decomposed wood debris. This is consistent our
understanding that uncontrolled fill with demolition debris from former waterfront mills has been
encountered between the playground and restroom building. Handholes HH -1 and HH -2
encountered and were terminated in fill within the existing lower play area.
2013-054 FR 4 IfWA GEoSCIENcFs INC.
September 18, 2014
HWA Project No. 2013-054-21
Recessional Outwash — Loose to dense, slightly silty to very silty, gravelly, sand was
encountered in the boreholes and test pits beneath the fill to the full depths explored (up to
21 feet). This unit was apparently deposited by glacial meltwater streams during recession of the
Puget Lobe ice sheet at the end of the Vashon Stade of the Fraser Glaciation. This unit exhibited
stratification in the test pits, with interbedded layers of sand with variable silt content.
At the time of drilling, ground water was observed in the boreholes at depths of approximately
7 feet in BH -1 and 5.5 feet in BH -2. On October 3, 2013, the ground water level in BH -2 was
measured at 5.6 feet below ground surface. However, BH -1 (bottom of boring at 21 feet) proved
to be a flowing artesian well, with water flowing at a low rate over the lip of the 1 -inch PVC
standpipe. On October 20, 2013, a standpipe was used to measure the height of the artesian
ground water in BH -1. The piezometric head was observed to be about 0.5 feet above the
ground surface.
In the test pits excavated this Spring, toward the end of the wet season, the depth of initial
ground water encountered ranged from 3.5 feet in the existing upper play area (test pit TP -6) to
5.5 to 9.5 feet in test pits TP -3, 4, and 5 at proposed tank and vault excavations. Test pit TP -6
was left open (with plywood cover) overnight and the City Parks crew noted that the water level
was up to approximately 4 to 5 inches below the ground surface. The latter three test pits were
left open for at least a couple hours in order to observe ground water seepage conditions, and
drawdown pump tests with a 20 gpm electric sump pump were conducted, before backfilling. A
ground water level recovery test was conducted in test pit TP -4. Observations of ground water in
these test pits are noted below:
TP®
Excavated 5/12/2014. Total depth =11.5 ft. Test pit area approx. 3 x 5 feet at bottom.
Time WL (ft) Action
09:05 Finished digging. Variable seepage from 5.5 to B feet.
11:15 9.5
11:47 9.1
11:50 9.1 Began pumping @ 20 gpm; 3 x 5 foot area.
11:50:30 11 Stopped pumping. It took 30 seconds to drawdown 1.9'.
Piezo installed to 11.0 ft, screened from 6 to 11 feet.
Water level on 5/13/2014 at 15:25 -- 2.63 ft TOC, 2.39 ft BGS
2013-054 FR 5 HWA GFoSciENCFs INC.
September 18, 2014
HWA Project No. 2013-054-21
TP -4
Excavated 5/12/2014. Total depth = 11.5 ft. Test pit area approx. 3 x 4 feet at bottom.
Time WL (ft) Action
09:50 Finished digging. Moderate seepage at 9.5 feet.
11:20 9.8
12:41 9.5 Began pumping @ 20 gpm. 3 x 5 foot area.
12:49 10.5 Stopped pumping. 3 x 4 foot area. It took 8 mins. to drawdown 1'.
13:11 10.1 Recovery. 3 x 4 foot area.
TP -5
Excavated 5/12/2014. Total depth = 11.0 ft. Test pit area approx. 3 x 2.5 feet at bottom.
Time WL (ft) Action
10:24
Finished digging. Variable seepage from 8.5 to 10 feet.
11:25 8.8
(No seepage visible)
12:05 8.5
Began pumping @ 20 gpm. 3 x 5 foot area.
12:27 10.1
12:33 10.5 Still pumping; pump just keeping up with ground water seepage.
It took 28 minutes to drawdown 2 feet (=10.5-8.5).
12:35 10.5 Stopped pumping. 3 x 2.5 foot area.
Piezo installed to 10.7 ft, screened in lower 5 feet.
Water level on 5/13/2014 at 15:31— 7.69 ft TOC, 7.85 ft BGS
In the test pits excavated in the Fall, ground water seepage was generally encountered at similar
levels; at 8.4 feet in TP -1 and 7.3 feet in TP -2. Where seepage was encountered below about 9.8
in TP -1 and 8.5 feet in TP -2, the flow was initially moderate to heavy; however the rates
diminished within minutes. In test pit TP -1, the rate diminished to approximately 3 gpm after 5
minutes (visual estimate), in a pit approximately 2 feet wide by 8 feet long within the seepage
zone. The water level in the pit from the seepage reached a near -static level of about 10.5 feet
after 10 minutes. In test pit TP -2, which measured approximately 3 by 7 feet within the seepage
zone, the seepage diminished to approximately 1 to 2 gpm after 10 minutes (visual estimate),
with the water level at about 12 feet.
2013-054 FR 6 HWA GEOSCIENCES INC.
September 18, 2014
HWA Project No. 2013-054-21
See Table 1 below for all measurements of static water level.
Table 1— Ground Water Level Data
Static Water Level, bgs (feet)
Exploration:
®ate I 13H-1 131-1-2 TP -1 TP -2 TP -3 TP -4 TP -5 TP -6
10/3/2013
(flowing)
5.60
10/20/2013
+0.5
5.60
1/14/2014
+0.54
5.52
5/12/2014
+0.28
5/13/2014
+0.61
5.77
2.89
7.85
0.33
We did not observe any ground water seepage from the ground surface in the vicinity of the
playground during any of our site visits. It is anticipated that ground water conditions at various
site locations will change in response to rainfall, time of year, and other factors.
XMIMMA11301MA"M ti:
Based on the ground water conditions encountered in the explorations, dewatering will likely be
necessary for the tank and vault excavations. We anticipate that dewatering can be accomplished
either with sump pumps within the excavations or a well point system.
Recommendations for soil bearing capacity, tank bouyancy mitigation, excavation shoring or
sloping and dewatering, mitigation of ground water seepage, general earthwork, and pavement
subgrade are provided in the following sections.
Temporary Excavations
Excavations up to 10 feet deep should be sloped or shored per WAC 296-155. If conventional
shoring systems are used they should be kept shallow (10 feet) so as not penetrate into flowing
artesian conditions as encountered in borehole BH -1. Alternatively, excavations could be sloped
to no steeper than 1.51-1: IV (Horizontal:Vertical) for worker safety.
2013-054 FR 7 HWA GEOSCIENCES INC.
September 18, 2014
HWA Project No. 2013-054-21
Dewatering will be necessary for all underground tank and utility excavations. The contractor
shall dewater the ground water to at least one foot below bottom of excavations, by using sumps
or well point systems as necessary. Ground water conditions may change in response to rainfall,
time of year, and other factors, such that higher ground water conditions could be encountered
during the wet season. Dewatering during construction is the responsibility of the contractor.
Baring Capacity
We recommend using a bearing capacity of 2,000 pounds per square foot (psf) for the medium
dense to dense soils encountered below the fill soils.
Buoyancy and Uplift for Underground Structures
The primary design concern for underground structures is buoyancy as the uplift forces on the
structures are large due to the artesian ground water condition and the perched ground water.
For buoyancy calculations, the design ground water level should be assumed to be one foot
above the existing ground surface, as shown on Figure 3. The resisting forces are the weight of
the soil above the structure and the frictional force along the sides of the structure or within the
soil above an extended base.
Selection and design of the water tank and stormwater vault structures must account for the large
bending moments that the slabs will be subject to from hydraulic uplift when the structures are
empty.
MITIGATION OF GRouND WATER SEEPAGE
We understand that ground water seepage was a problem during construction of the playground,
such that a series of subsurface drains was constructed in the upper play area, as well as a 4 -foot
deep footing drain above the upper retaining wall. According to Rich Lindsay, there are no
current instances of ground water seepage in or around the playground, though he noted there are
other seepage locations in the park. A system of perforated underdrains should be installed
within the proposed play areas and spray area to intercept ground water seepage and direct it
away from the subgrade.
We anticipate ground water seepage will reach the ground surface after backfilling, unless
underdrains are installed similar to those for the play areas.
2013-054 FR 8 IIWA GEOSUENCES INC.
September 18, 2014
HWA Project No. 2013-054-21
Temporary Excavations
Any temporary excavations deeper than 4 feet should be sloped or shored in accordance with
current State of Washington Labor and Industries Safety and Health guidelines. Per these
guidelines, any fill, alluvial soils and recessional outwash are classified as Type C soils.
Unsupported excavations within Type C soils should be sloped no steeper than 1.5H:1 V. The
recommended maximum slope is applicable to temporary excavations above the water table
only; flatter side slopes would be required for excavations below the water table and/or where
seepage is occurring. Seepage areas of exposed slopes shall be covered with a crushed rock
layer. Minor sloughing shall be contained by placing ecology blocks at the toe of the slopes.
Structural Fill and Compaction
For the purposes of this report, material used to raise grades, backfill excavations and pipeline
trenches, or placed for purposes of preparing pavement Subgrade, is classified as structural fill.
In general, imported structural fill should consist of clean, relatively free -draining, granular soils
that are free from organic matter or other deleterious materials. Such materials should comprise
particles of less than 4 -inch maximum dimension, with less than 7% fines (portion passing the
U. S. Standard No. 200 sieve), as specified for "Gravel Borrow" in Section 9-03.14(1) of the
WSDOT Standard Specifications (WSDOT, 2014). The fine-grained portion of structural fill
soils should be non -plastic. Soils excavated from the site are likely to be suitable for structural
fill, but based on the variability of existing fill it should be evaluated by the geotechnical
engineer at the time of construction.
Structural fill soils should be moisture conditioned as needed, placed in loose horizontal lifts less
than 8 -inches thick, and compacted to at least 95% of the maximum dry density as determined
using test method ASTM D1557 (Modified Proctor). Achievement of proper density of a
compacted fill depends on the size and type of compaction equipment, the number of passes,
thickness of the layer being compacted, and soil moisture -density properties. In areas where
limited space restricts the use of heavy equipment, smaller equipment can be used, but the soil
must be placed in thin enough layers to achieve the required relative compaction. Generally,
loosely compacted soils result from poor construction technique and/or improper moisture
content. Soils with high fines contents are particularly susceptible to becoming too wet and
coarse-grained materials easily become too dry, for proper compaction.
Pavement Subgrade Preparation
All pavement structures shall have under -drains which shall be tied to the storm water drain
systems. Subgrade preparation for pavement construction within the Spray and Play Area should
consist of stripping the surficial organics and removing any other deleterious materials. In areas
of competent subgrade consisting of granular soils, such as observed in the two handholes, the
2013-054 FR 9 IfWA GEOSCIENCES INC.
September 18, 2014
HWA Project No. 2013-054-21
exposed subgrade should be proof -rolled with a roller or fully loaded dump truck prior to placing
the base course. Any soft and yielding materials identified during the proof -rolling process
should be removed and replaced with structural fill. If necessary, and as may be directed by the
geotechnical engineer, a soil separation grade geotextile and/or geogrid may be required to be
placed on the exposed subgrade for support of the structural fill.
Crushed surfacing base/top course and structural fill should be compacted to at least 95% of the
maximum dry density, as determined using test method ASTM D 1557 (Modified Proctor).
Wet Weather Earthwork
Existing site soils are moisture sensitive to varying degrees, and may be difficult to handle or
traverse with construction equipment during periods of wet weather. Therefore, general
recommendations relative to earthwork performed in wet weather or in wet conditions are
presented below. These recommendations should be incorporated into the contract specifications
and should be required when earthwork is performed in wet conditions:
1) Site stripping and fill placement should be accomplished in small sections to
minimize exposure to wet weather. Excavation or removal of unsuitable soil should
be followed promptly by placement and compaction of a suitable thickness of clean
structural fill. The size and type of construction equipment used may have to be
limited to prevent soil disturbance.
2) Material used as structural fill should consist of clean granular soil, of which not
more than 5% passes the U.S. Standard No. 200 sieve, based on wet sieving the
fraction passing the 3/4 -inch sieve. The fine-grained portion of structural fill soils
should be non -plastic.
3) No soil should be left uncompacted so it can absorb water. Stockpiles of excavated
soil should either be shaped and the surface compacted, or be covered with plastic
sheets. Soils that become too wet should be removed and replaced with clean
granular materials.
4) Excavation and placement of fill should be monitored by a geotechnical inspector to
determine that the work is being accomplished in accordance with the project
specifications and the recommendations contained herein.
� �° ► 1 � �fy\x;17:11 ►� I`II Ir Il G7►f
We have prepared this report for the City of Edmonds and its agents for use in design and
construction of a portion of this project. This report should be provided in its entirety to
prospective contractors for bidding and estimating purposes; however, the conclusions and
interpretations presented in this report should not be construed as our warranty of the subsurface
2013-054 FR 10 HWA GEOSCIENCES INC.
September 18, 2014
HWA Project No. 2013-054-21
conditions. Experience has shown that soil and ground water conditions can vary significantly
over small distances. Inconsistent conditions can occur between explorations and may not be
detected by a geotechnical study of this limited nature. If, during future site operations,
subsurface conditions are encountered which vary appreciably from those described herein,
14WA should be notified for review of the recommendations of this report, and revision of such
if necessary.
Sufficient geotechnical monitoring, testing, and consultation should be provided during
construction to confirm that the conditions encountered are consistent with those indicated by
explorations, to provide recommendations for design changes should conditions revealed during
construction differ from those anticipated, and to verify that the geotechnical aspects of
construction comply with the contract plans and specifications.
Within the limitations of scope, schedule and budget, HWA attempted to execute these services
in accordance with generally accepted professional principles and practices in the fields of
geotechnical engineering and engineering geology in the area at the time the report was prepared.
No warranty, expressed or implied, is made. The scope of our work did not include
environmental assessments or evaluations regarding the presence or absence of wetlands or
hazardous substances in the soil, surface water, or ground water at this site, nor the impact of this
project upon existing conditions or the impact of existing conditions other than geotechnical on
the project.
HWA does not practice or consult in the field of safety engineering. We do not direct the
contractor's operations, and cannot be responsible for the safety of personnel other than our own
on the site. As such, the safety of others is the responsibility of the contractor. However, the
contractor should notify the owner if he considers any of the recommended actions presented
herein unsafe.
®-®
2013-054 FR 11 HWA GEOSCIENCES INC.
September 18, 2014
HWA Project No. 2013-054-21
We appreciate the opportunity to provide geotechnical services for this project. Should you have
any questions, or if we may be of further service, please contact us at your convenience.
Brad W. Thurber, L.E.G.
Senior Engineering Geologist
BWT:SHH
Sa H. Hong, P.E.
Principal Geotechnical Engineer
Attachments:
Figure 1 Vicinity Map
Figure 2 Site and Exploration Plan
Figure 3 Parameters for Calculating Uplift Resistance of Tanks
Appendix A Field Explorations
Appendix B Laboratory Testing
2013-054 FR 12 HWA GEOSCIENCES INC.
September 18, 2014
HWA Project No. 2013-054-21
1101 W'DI
Booth, D.B., Cox, B.F., Troost, K.G., and Shimel, S.A., 2004, Composite Geologic Map of the
Sno-King area: University of Washington, Seattle -Area Geologic Mapping Project, scale
1:24,000.
WSDOT, 2014, Standard Specifications for Road, Bridge, and Municipal Construction,
Washington State Department of Transportation Publication M 41-10.
2013-054 FR 13 HWA GEOSCIENCES INC.
5:\2013 Projects\2013-054-21 Edmonds City Park Play & Spray Area Revitalization\CADTIG 1 2013-054.docx
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SYMBOL
ASSUMPTIONS
B =
Width of extended base in feet
(1®foot minimum)
Soil Unit Weight = 130 pcf
Soil Friction Angle
= 35®
W =
Structure weight in kips
At—rest Pressure
Coefficient = 0.43
WB =
Total soil weight above base in kips
Buoyant Soil Unit
Weight = 66 pcf
WS =
Buoyant weight of soil above
structure in kips
NOTES
FB =
Buoyant force in kips
Factor of Safety
= W+FSW L+FSS L
=
Unit weight of water x volume of
FB
structure below design ground—water level
(without extended
base,
as indicated on
the left side)
L =
Perimeter around base of wall in feet
Fss =
Shearing resistance of soil without
Factor of Safety
= W + W® + FS L
extended base
FB
=
0.0071(HS2)
(with extended base
(in kips per foot of wall)
around perimeter
of structure,
FSW =
Shearing resistance of soil—wall contact
as indicatedpn the right side
of this figure)
=
0.0050(H2—HS2)
(in kips per foot of wall)
FS =
Shearing resistance of soil with
extended base
=
0.0071(H2 )
(in kips per foot of wall)
PARAMETERS FOR CALCULATING
ff _��05 UPLIFT RESISTANCE OF TANKS
0 INC CITY PARK PLAY AND
ZU SPRAY REVITALIZATION
S:\2013 PROJECTS\2013-054-21 EDMONDS CITY PARK PLAY & SPRAY AREA REVITALIZATION\CAD\UPLIFT.DWG <8.5x11 Figure 3> Plotted: 11/13/2013 6:42 PM
r, � � �:
RELATIVE DENSITY OR CONSISTENCY VERSUS SPT N -VALUE
COHESIONLESS SOILS
COHESIVE SOILS
Boulders
Gravel and
Cobbles
910
GW
Approximate
Density
N (blows/ft)
Approximate
Consistency
N (blows/ft)
Undrained Shear
Grained
Gravelly Soils
Relative Density(%)
No. 10 (2.0 mm) to No. 40 (0.42 mm)
Fine sand
—
Silt and Clay
Smaller than No. 200 (0.074mm)
MR
o Q
GP
Strength (psf)
Very Loose
0 to 4
0 - 15
Very Soft
0 to 2
<250
Loose
4 to 10
15 - 35
Soft
2 to 4
250 - 500
Medium Dense
10 to 30
35 - 65
Medium Stiff
4 to 8
500 - 1000
Dense
30 to 50
65 - 85
Stiff
8 to 15
1000 - 2000
Very Dense
over 50
85 - 100
Very Stiff
15 to 30
2000 - 4000
Sand and
Clean Sand
Hard
I over 30
>4000
USCS SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GROUP DESCRIPTIONS
Boulders
Gravel and
Cobbles
910
GW
Well -graded GRAVEL
Coarse
3 in to 314 in
Clean Gravel
®&
Sand
No. 4 (4.5 mm) to No. 200 (0.074 mm)
Grained
Gravelly Soils
(little or no fines)
No. 10 (2.0 mm) to No. 40 (0.42 mm)
Fine sand
—
Silt and Clay
Smaller than No. 200 (0.074mm)
MR
o Q
GP
oody-graded GRAVEL
Solis
Pocket Penetrometer
Approx. Compressive Strength (tsf)
SG
Specific Gravity
TC
More than
TV
Torvane
Approx. Shear Strength (tsf)
UC
50% of Coarse
Gravel with
o
GM
Silty GRAVEL
Fraction Retained
Fines (appreciabledwl
on No. 4 Sieve
amount of fines)
GC
Clayey GRAVEL
Sand and
Clean Sand
,•
SW
Welkgraded SAND
More than
Sandy Soils
(little or no fines)
SP
Poorly -graded SAND
50% Retained
50% or More
on No.
Sand with
SM
Silty SAND
200 Slave
of Coarse
Fines (appreciable
Fraction Passing
Size
amount of fines)
SC
Clayey SAND
No. 4 Sieve
ML
SILT
Fine
Silt
CL
Lean CLAY
Grained
and Liquid Limit
Soils
Less than 50%
Clay
_
—
OL
Organic SILT/Organic CLAY
MH
Elastic SILT
50% or More
Silt
Liquid limit
Passing
50% or More
CH
Fat CLAY
No. 200 Sieve
Clay
Size
OH
Organic SILT/Organic CLAY
Highly Organic Soils
` r
PT
PEAT
COMPONENT DEFINITIONS
COMPONENT
SIZE RANGE
Boulders
Larger than 12 in
Cobbles
3 in to 12 in
Gravel
3 in to No 4 (4.5mm)
Coarse gravel
3 in to 314 in
Fine gravel
3/4 in to No 4 (4.5mm)
Sand
No. 4 (4.5 mm) to No. 200 (0.074 mm)
Coarse sand
No. 4 (4.5 mm) to No. 10 (2.0 mm)
Medium sand
No. 10 (2.0 mm) to No. 40 (0.42 mm)
Fine sand
No. 40 (0.42 mm) to No. 200 (0.074 mm)
Silt and Clay
Smaller than No. 200 (0.074mm)
SAMPLE TYPE SYMBOLS
®2.0" OD Split Spoon (SPT)
(140 Ib. hammer with 30 in. drop)
Shelby Tube
3-1/4" OD Split Spoon with Brass Rings
OSmall Bag Sample
Large Bag (Bulk) Sample
Core Run
Non-standard Penetration Test
(3.0" OD split spoon)
GROUNDWATER SYMBOLS
jz Groundwater Level (measured at
time of drilling)
- Groundwater Level (measured in well or
open hole after water level stabilized)
PROPORTION RANGE
TEST SYMBOLS
%F
Percent Fines
AL
Atterberg Limits: PL = Plastic Limit
12-30%
LL = Liquid Limit
CBR
California Bearing Ratio
CN
Consolidation
DD
Dry Density (pcf)
DS
Direct Shear
GS
Grain Size Distribution
K
Permeability
MD
Moisture/Density Relationship (Proctor)
MR
Resilient Modulus
PID
Photoionization Device Reading
PP
Pocket Penetrometer
Approx. Compressive Strength (tsf)
SG
Specific Gravity
TC
Triaxial Compression
TV
Torvane
Approx. Shear Strength (tsf)
UC
Unconfined Compression
SAMPLE TYPE SYMBOLS
®2.0" OD Split Spoon (SPT)
(140 Ib. hammer with 30 in. drop)
Shelby Tube
3-1/4" OD Split Spoon with Brass Rings
OSmall Bag Sample
Large Bag (Bulk) Sample
Core Run
Non-standard Penetration Test
(3.0" OD split spoon)
GROUNDWATER SYMBOLS
jz Groundwater Level (measured at
time of drilling)
- Groundwater Level (measured in well or
open hole after water level stabilized)
PROPORTION RANGE
DESCRIPTIVE TERMS
<5%
Clean
6-12%
Slightly (Clayey, Silty, Sandy)
12-30%
Clayey, Silty, Sandy, Gravelly
30-60%
Very (Clayey, Silty, Sandy, Gravelly)
Components are arranged in order of increasing quantities.
NOTES: Soil classifications presented on exploration logs are based on visual and laboratory observation.
Soil descriptions are presented in the following general order: MOISTURE CONTENT
Density/consistency, color, modifier (if any) GROUP NAME, additions to group name litany), moisture DRY Absence of moisture, dusty,
content. Proportion, gradation, and angularity of constituents, additional comments. dry to the touch.
(GEOLOGIC INTERPRETATION) MOIST Damp but no visible water.
Please refer to the discussion in the report text as well as the exploration logs for a more WET Visible free water, usually
complete description of subsurface conditions. soil is below water table.
LEGEND OF TERMS AN#
OVA City Park Play & Spray Area Revitalization SYMBOLS
HWEOSCOM INC Edmonds, Washington EXPLORATION LOGS
PROJECT NO.: 2013-054 FIGURE: A-1
LEGEND 2013-054.GPJ 11/13/13
DRILLING COMPANY: Geologic Drill, Inc. SURFACE ELEVATION: 25.00 * feet DATE STARTED: 9/23/2013
DRILLING METHOD: HSA, MT52 mini -track CASING ELEVATION * feet DATE COMPLETED: 9/23/2013
SAMPLING METHOD: SPT w/ cathead LOGGED BY: B. Thurber
LOCATION: N. of playground, see Figure 2
U)
g
U
J
J 0
N a.^ m U)0
O �� N D
0 1-7.� Sod and topsoil
SM I Gravelly drill action.
5-
-
10-
10-
15-
15 -
20-
20 -
25-
25 -
Dense, olive brown, slightly silty, fine gravelly, fine to S-1 6-23-35
medium SAND, moist. Blow counts overstated.
(FILL)
----------------------
Dense, olive brown, gravelly, silty, fine to medium SAND, S-2 14-23-18
moist. No bedding.
SM
11�
W
O
.. ....
5
0.
W
m
�
z^
L r
N
w 0
medium SAND, wet.
z
l)
W
i -~
W
a
W
s
._
wo co
�
W
g
— — — — — — — — — — — — — — — — — — — — — —
3W
O W_
S-4 10-10-8 GS
0
to medium SAND, wet. Scattered fine gravel. Finely
DESCRIPTION ai
vi
a n
O
_ 0
Dense, olive brown, slightly silty, fine gravelly, fine to S-1 6-23-35
medium SAND, moist. Blow counts overstated.
(FILL)
----------------------
Dense, olive brown, gravelly, silty, fine to medium SAND, S-2 14-23-18
moist. No bedding.
SM
Gravelly drill action at 7 feet.
.. ....
5
Dense, rust -mottled olive brown, silty, gravelly, fine to
S-3 12-16-17
medium SAND, wet.
:........:....:....:....:....
10
(RECESSIONAL OUTWASH)
SM
— — — — — — — — — — — — — — — — — — — — — —
Medium dense, rust -mottled olive brown, slightly silty, fine
S-4 10-10-8 GS
to medium SAND, wet. Scattered fine gravel. Finely
bedded.
Medium dense, olive brown, silty, fine to medium SAND,
S-5 7-9-8
wet. 1 -inch lens of medium to coarse sand.
Dense, olive gray, clean to silty, fine to medium SAND, wet.
S-6 9-14-17 GS
:•
Scattered fine gravel.
Sand heave in auger before sampling at 20 feet. Blow
counts overstated due to heave, and terminated after 12
inches.
S-7 15-37
Poor recovery (heave): Olive brown, slightly silty, fine to
medium SAND, wet.
Borehole terminated at 21 feet.
Ground water encountered at approx. 7 feet during drilling.
1 -inch PVC piezometer installed to 19.8 feet. Flowing
artesian well, observed on 10/3/2013.
Water level measured at 0.5 feet above ground surface on
10/20/2013.
DOE well # BIJ 367
NOTE:
NOTE: This log of subsurface conditions applies only at the specified location and on the date indicated
and therefore may not necessarily be indicative of other times and/or locations.
Standard Penetration Test
(140 Ib. weight, 30" drop)
® Blows per foot
0
10 20 30 40 50
r]
. A ..:.... :.... :.... 1�_15 1
20
`— 25
0 20 40 60 80 100
Water Content (%)
Plastic Limit ' ' Liquid Limit
Natural Water Content
.. ....
5
:........:....:....:....:....
10
r]
. A ..:.... :.... :.... 1�_15 1
20
`— 25
0 20 40 60 80 100
Water Content (%)
Plastic Limit ' ' Liquid Limit
Natural Water Content
DRILLING COMPANY: Geologic Drill, Inc.
SURFACE ELEVATION:
31.00 1 feet
DATE STARTED: 9/23/2013
DRILLING METHOD: HSA, MT52 mini -track
CASING ELEVATION
(RECESSIONAL OUTWASH)
1 feet
X.
DATE COMPLETED: 9/23/2013
SAMPLING METHOD: SPT w/ cathead
SAND, moist. _____________ __
11-21-22
SM
Dense, olive gray, slightly silty to silty, fine gravelly, fine to
LOGGED BY: B. Thurber
LOCATION: E. of playground, see Figure 2
Loose, olive brown with minor rust banding, slightly silty to
S-3 54-5
silty, fine gravelly, fine to medium SAND, wet. Finely
bedded.
Medium dense, olive brown, slightly fine gravelly, slightly
S4 6-10-15 GS
silty to silty, fine to medium SAND, wet.
U)
w
W
z
Ground water encountered at approx. 5.5 feet during
Standard Penetration Test
U
m
?
s
t-
w v
(140 Ib. weight, 30" drop)
DOE well # BIJ 368
w
g ¢
®Blows per foot
-i
0 U)��
w
w
a� Co U 2
2
zo
z
E-
Nx
a �,
W
W >-U)
o U) D DESCRIPTION
Q
U)
Q
m
w—
°-
O
U
a. U) 0
10 20 30 40
y
50
Sod & Topsoil
0
5-
15-
1 20-
1
0-
1 25 -
NOTE: This log of subsurface conditions applies only at the specified location and on the date indicated
and therefore may not necessarily be indicative of other times and/or locations.
I
11
1
10 1
15 1
11-20 1
25
0 20 40 60 80 100
Water Content (%)
Plastic Limit Liquid Limit
Natural Water Content
Loose, reddish brown grading to dark yellow brown, silty,
S-1 344
gravelly, fine to medium SAND, moist.
(RECESSIONAL OUTWASH)
X.
Medium dense, reddish brown slightly silty, fine to medium
SAND, moist. _____________ __
11-21-22
SM
Dense, olive gray, slightly silty to silty, fine gravelly, fine to
�S-2a
S -2b GS ; . -
coarse SAND, wet.
Loose, olive brown with minor rust banding, slightly silty to
S-3 54-5
silty, fine gravelly, fine to medium SAND, wet. Finely
bedded.
Medium dense, olive brown, slightly fine gravelly, slightly
S4 6-10-15 GS
silty to silty, fine to medium SAND, wet.
Borehole terminated at 11.5 feet.
Ground water encountered at approx. 5.5 feet during
drilling.
1 -inch PVC piezometer installed to 10 feet.
Water level at 5.60 feet bgs (5.36 feet TOC) on 10/3/2013.
DOE well # BIJ 368
NOTE: This log of subsurface conditions applies only at the specified location and on the date indicated
and therefore may not necessarily be indicative of other times and/or locations.
I
11
1
10 1
15 1
11-20 1
25
0 20 40 60 80 100
Water Content (%)
Plastic Limit Liquid Limit
Natural Water Content
DRILLING COMPANY: HWA Geosciences Inc. SURFACE ELEVATION:
23.00 A feet
DATE STARTED: 10/10/2013
DRILLING METHOD: Posthole Digger & Hand Auger CASING ELEVATION
:k feet
DATE COMPLETED: 10/10/2013
SAMPLING METHOD: Grab
LOGGED BY: B. Thurber
LOCATION: See Figure 2
gravelly, fine to coarse SAND, moist.
co
W
U a
in
z
la- W
h
Q
N
J �
U
N
W
N
J 0 W
W
W cfl
i
~
�
Z
v
_
F
m co a-
a
W
M
0
i-
CL
W
U) � DESCRIPTION vai
vQi
0
a
O
0
a
0
0
' y• • Shredded Wood Chips over Geotextile fabric.
Pj • �t l
Q GP Pea Gravel
0
1
0
1
`. SM Dense, grayish -brown, silty, gravelly SAND, moist.
(FILL)
�'. SM Dense, yellow brown, slighlty silty to silty
2
2
Handhole terminated at 2.3 feet due to refusal on gravel.
No ground water seepage observed during excavation.
3
3
4
4
5
5
0 20 40 60 60 100
Water Content (%)
Plastic Limit Liquid Limit
Natural Water Content
NOTE:
This log of subsurface conditions applies only at the specified location and on the date
indicated
and therefore may not necessarily be indicative of other times and/or locations.
, fine to coarse
gravelly, fine to coarse SAND, moist.
DRILLING COMPANY: HWA Geosclences Inc. SURFACE ELEVATION: 23.00 :k feet DATE STARTED: 10/10/2013
DRILLING METHOD: Posthole Digger & Hand Auger CASING ELEVATION feet DATE COMPLETED: 10/10/2013
SAMPLING METHOD: Grab LOGGED BY: B. Thurber
LOCATION: See Figure 2
W
0
0—
M
2 -
Cie
4-
5 -
0 20 40 60 80 100
Water Content (%)
Plastic Limit Liquid Limit
Natural Water Content
NOTE: This log of subsurface conditions applies only at the specified location and on the date Indicated
and therefore may not necessarily be indicative of other times and/or locations.
F_
il
Lij
0
0
d
U)
Lu
W
Co
z
Lu
_j
0-
z
ul
0
U)
ui
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ui
_j
W
z
ca
2
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0
a.
M
cL
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z
W
X 0
>-
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:3
DESCRIPTION
<
(n
<
U)
UJ
M
ly
0 (9
Shredded Wood Chips over Geotextile fabric.
0 bc
GP
Pea Gravel
SM
Dense brown and bluish -gray, sandy, silty, fine to coarse
GRAVEL, moist.
(FILL)
SM
----------------------
Dense, dark brown, organic, silty, fine to coarse gravelly,
I'
fine to medium SAND, moist.
_j
Handhole terminated at 2.2 feet due to refusal on gravel.
No ground water seepage observed during excavation.
0 20 40 60 80 100
Water Content (%)
Plastic Limit Liquid Limit
Natural Water Content
NOTE: This log of subsurface conditions applies only at the specified location and on the date Indicated
and therefore may not necessarily be indicative of other times and/or locations.
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From: Steve Hatzenbeler <SteveH@Ipdengineering.com>
Sent:
Tuesday November 2Ei2O143:39PK4
To:
DeLiUa,Mike; Shuster, Jerry
�m
Cc:
Brian Bishop; Hite, Carrie; Zu|autJoAnne
Subject:
RE: Spmypark2nd round review comments
Mike,
See below from Sa Hong at HWA Geosciences, Inc. regarding the buoyancy analysis forthe MHs. Also, attached is an
updated calculation spreadsheet with the current analysis. One thing vve did revise in the attached analysis is to correct
the volume calc to be based on the outer diameter of the structures. We have also included a calculation for the
shearing resistance force in the factor of safety calc. With this update, there is a factor of safety of 1.71 for the SS lift
station MH,and 1.67for the SDK4Hsonthe detention tank.
Regarding the discrepancy between PACE's analysis and ours as it relates to the depth of groundwater above the
surface, we cannot explain the basis for their calculations, but we have a high degree of confidence in ours, as does the
project's geotechnical engineer.
Please review and let us know Uyou have any concerns.
Thanks,
Steve liN(� [
V���'
veHatzenhmler,P.E,LEEOAP
D Engineering'PLLC
ne: 206.725.1211
Dear Steve,
It is my firm belief that the buoyancy uplift forces for a fully submerged object shall be equivalent to the volume of
water displaced bvthe object, regardless ofthe depth ofwater.
o A 5 foot diameter manhole which weighs 17,500 lbs in the air per manufacturers specification.
* Buoyancy uplift= (5^2*3.14/4)*10ft*62.4pcf=12,246 lbs
~ FSagainst up|ift=17,SOO/1Z,246=1.43
As long asthe object iscompletely submerged, the water depth above the structure shall not change the buoyant uplift
force. Uplift is the same for all depths of water as long as the volume of the object stays the same, as the manhole is
considered asarigid object and its volume does not change inthis case.
Sa Hong, P.E.
Geotechnical Engineer, Principal
HUVAGeoSciencesInc.
Office: 425.774.0106 (ext.238) I Cell: 206.794.3'125
From. DeL|k�Mike [nlaiKo:Mike. DeL|b@edn)ondswa.00v]
Sent: November 25, 2014 12:48 PM