LANDAU - Preliminary Geotechnical Investigation 073091.pdfL A i� DAU
ASSOCINFES,
INC.
Ge k:: rero- rcnr:�1 Engb)serrq r! uYF u'ugi:)s
RECEIVED
J 111. 3 0 1991
COMMDIREECS SERVICES
July 30, 1991
City of Edmonds.
250 Fifth Avenue North
Edmonds, WA 98020
Attention:' Mr. Peter Hahn
REI i'RELIMINARY GEOTECHNICAL INVESTIGATION
EDMONDS SHOPPING CENTER
EDMONDS, WASHINGTON
This letter presents the results of our preliminary geotechnical investigation for the
Edmonds Shopping Center property, located at the northwest corner of the intersection of
Dayton Street and State Route 104 (Sunset Avenue) in Edmonds, Washington. The purpose of
our services was to provide information regarding the property's geologic condition and
geotechnical considerations related to potential future site development. Our work has been
accomplished in general accordance with the scope of services described in Supplemental No.
1 to our agreement with the City of Edmonds (City) dated June 11, 1991.
The site is approximately 4.4 acres in size, relatively- flat (gentle upward slope to the
north and east), and is located northwest of the intersection of Dayton Street and State Route
104. The site is presently asphalt paved and was occupied by a Safeway food store and several
small businesses in attached strip malls at the time of our field work
Structures at the site do not appear to show exterior distress. A conversation with a
Safeway employee indicated that interior floor warping is present within the food store. The
existing pavement is moderately patched and shows some signs of settlement, particularly
towards the edges of the parking lot.
Document Review
Several sources of geotechnical information for the site and nearby properties were
reviewed. The information from these sources, combined with information from our exploratory
borings, is the basis for our preliminary assessment of geologic conditions and development
considerations for the site. The following information sources, from our files and the City of
Edmonds' records, were reviewed:
01/30/91 EDM0ND6\HAHN".tZr
P.U. fiOX 1629 • FDP'i NDS, AASi{I L f(Ih ` SO20-v1.Y • +_'t)5) ?o -i iO' • 1;1X i.a bi' ;< a:"�
• Boring logs for the site from an investigation performed by Pittsburgh Testing
Laboratory, March 12,1966
• Boring Logs from the Comprehensive Sewerage Plan, Reid Middleton and
Associates, March 31, 1969; fox property at southeast intersection of State
Route 104 and Dayton Street .
• Washington State Department of Highways Soils Report -for State'Route 104,
Ferry St. to 5th Ave., November 1, 1967
• Boring Logs by Washington State Department of Highways for Dayton St.
Sewer Line, March 1970
• Various geotechnical reports and letters for the Harbor Square Development
at the southwest corner of Dayton Street and State Route 104, by Hemphill
Consulting .Engineers, including Edmonds Athletic Club, Building No. 6
(October 8,1984); Edmonds Athletic Club, Building No. 6 (December 10,1984);
Harbor Inn Hotel, Building No. 8 (February 25,1984); Harbor Square, Building
No. 2 (February 25,1984)
• Geotechnical report for Alaska NW Publishing Co. by Charles C. May
Consulting Engineers, June 22, 1974
• Geotechnical report for Alaska Magazine Warehouse by Neil Twelker and
Associates, December 21, 1976
• Geotechnical report for Alaska NW Publishing Co. Addition by Neil Twelker
and Associates, February 7,1978
• Geotechnical report for South County Senior Center Addition by Cascade
Testing Laboratory, Inc., August 15,1976.
Subsurface Conditions
In addition to a review of available information, three soil borings were completed at the
site to further characterize existing site conditions. These borings were advanced to depths of
19 to 23 ft;• boring locations are shown on the Site Map, Figure 1. Soils encountered during
boring advancement were classified in accordance with the soil classification system presented
in Attachment 1. Logs of these explorations are also attached (Attachment 2).
The site is underlain by fill overlying soft organic silt. The organic silt is underlain by
a variable thickness of medium dense to very dense sand and gravel deposits, which are
underlain by glacial ti1L The fill consisted of 4.5 to 7.5 ft of medium dense silty sand and gravel.
The organic silt ranged from about 2.5 to 10 ft thick in the Landau Associates' borings, has a
very soft to soft consistency, and includes silt, variable amounts of organics, and occasional
peat. Native soils beneath the silt/organic layer include medium dense to very dense, dean
07/30/91 EDMON KAHN IET 2 LANDAU ASSOCLAI 0,
sand and gravel and silty sand. Groundwater was encountered at the time of drilling•at 9.0 to
14.0 ft below the existing ground surface, although static water levels may be shallower. The
subsurface conditions encountered in the Landau Associates' borings are consistent with those
anticipated based on our document review.
General Site Development
Subscirface conditions are generally conducive to future site development. However, the
soft organic sails at the site are susceptible to significant settlements, even under relatively light
loading conditions. Consequently, all buildings or settlement sensitive structures should be
founded on piles extended at least to the sand and gravel units underlying native soft/organic
soils. Depending on the design loads, it may be necessary to extend piles into the glacial till,
anticipated to be present at depths of 20 ft or more below existing site grades. With proper site
preparation, typical floor loads can be supported on structural slabs placed at the existing site
grades. If the grade in the floor slab area is raised, or if high floor loads are anticipated, it may
be necessary to preload the floor slab area to minimize post construction settlements, or support
floor slab loads on piles.
If the existing site grade is raised over large areas, areal settlement is anticipated. To
mm
inimize areal settlements subsequent to construction, it aybe necessary to place preload fill
prior to construction or grading. Our observations of existing parking lot pavement performance
also indicate possible differential settlement at the site. Minimizing site grade changes and
preloading can reduce the magnitude of differential settlements. Because of the high likelihood
of"site,settlernehf, flexible utility connections to main utility lines and structures may be
advisable. The length of time and amount of preload required would be dependent on specific
subsurface conditions, design site grades and loadings, and construction schedules.
Use of this Letter
Landau Associates has provided these preliminary geotechnical recommendations for the
City of Edmonds to aid in the evaluation of the Edmonds Shopping Center property. The
recommendations made in this letter are based on assumptions that site soil conditions were
reasonably defined by our field explorations and document review. Our recommendations are
preliminary and are not appropriate for use as the basis of site development or design. Should
the City purchase the property, additional geotechnical investigation, laboratory testing, and
engineering analyses are recommended once site development plans are available.
07r30191 EDMONM\HAHN{ NIEr 3 T 1NT.) A ; SSS i �:�. ,•;c.
'^ Landau Associates has performed this preliminary geotechnical investigation in
accordance with generally accepted engineering practices in effect in the Snohomish County area
at the time the services were provided. This warranty stands in lieu of all other warranties,
express or implied. While this report can'be used as a guide, it must be understo6d that it is
neither a rejection nor an endorsement of the site. y
We appreciate the opportunity of working with the City of Edmonds on this project and
look forward to assisting you in the future. Please contact us if you have any questions
regarding the information contained in this report.
LANDAU ASSOCIATES, INC.
F
By.
aw�
rence . Beard, P.E.
Project M eager
and
Deborah Ladd
Senior Staff Engineer
LDB/DL/nb
No. 74-31.10
Attachments
07/n/91 MMONM\HAHI3o92 IM 4 L1ti4
i
James Sliest
A_ KEY
Imo` N t9 B-1 B-3 ' Approximate Boring
l Location and ident'rfication
Parking 1
Restaurant
Shops Parking
\ G�
® B-2
i SAFEWAY
Parking
Shops /
5 i
B-3 5ro4 i�'
e0� HARBOR
SOUARE
i
/ 0�0
Parking � Oa
8
0 100 200
Adapted from Alan Gerard Approximate Scale In Feet
S Design incorporated (1984):
Site Map Figure 1
5
N
e
N
SOIL CLASSIFICATION SYSTEM
MAJOR GRAPHIC LETTER (t) nFSTYPICPALTIO(2)(3)
Notes: 1. (heal Iattk symbols 0.e., SM -5P) for a sand or gravel k dicwA a soll with an ostimaled S -t 5% lines. Multiple letter symbols (i.e.. ML/CL) indIcates
borderline Of ML49PIO soil dassilfcatlons. Only the lust tetter symbol's rospecdve pattern is shorn on logs. DemeP Han and IdwUNCE1tlon of SOU
2. Sal dasatptbns shorn an logs use the temrirsdogy and general approach fm the Vbual-ALvhra► Procedue.
as oullined In ASTM D 2486.
3. Sall desadptions (whlch are based on estimated values) are as Idlows: primary Soil Type(s) - Le.,'GRAVEL'.'SAND'.'SILT`, CLAY', etc.
secondary Soll Type(s) (:.16%) • i.e.. •gravotly'.'sandy. 'clayey'. etc.
Modif-ier(s) (a5% and Sts%) - I.e., -with graver.'sw4h sand',1Nith day', etc.
Mnor Component(s) (SS%) - i.e.. -trace graver.trace sand'.'Irace day', etc.
Soil Classification System
Attachment 1
DIVIyIONS
SYMCUU
tt
Weli.graded gravel: gravel1sand MWe(s):
CLEAN
p. a
GW
Aril& or no fines
GRAVEL AND
GRAVELLY SOIL
GRAVEL
(Little or
o :�;
Poorty-graded gravel; gtavellsand mixture(s);
no fuses)
.. O
.• �.
GP
fit0e al' no firm :
M --
(fibre than W16
of coarse fraction
GRAVEL
GM
Silty gravel; gravel/sandlsllt mixture(s)
0 e
v c,
retained on
84 sieve)
WITH FINES
(Appreciable
GC
Clayey gravel; graveltsariftift trift"(s)
W
zoo+
amount of fines)
CLEANf
' ' .r.•
'� �; � �=:�::
$W
Well -graded sand; gravelly sand; little or no fines
OSAND
ut cd
SAND AND
-S
SANDY SOIL
(Little or
SP
Poorly -graded sand; gravelly sand; little or no fines
� I6
no tines)
;;;
0:2 a
(Wre than SEW.
fraction
SAND
$M
.
Siiry sand; sand/sit mixtures}
of coarse
passed through
WITH FINES
#4 sieve)
(Appreciable'
SC
Clayey sand; sand/day mixture(s)
amount of fines)
Inorganic silt and very fine sand; rock flour; silty- or
ML
clayey -fine sand or clayey silt with slight plasticity
H o
SILT AND CLAY
Inorganic day of low to medium plasticity: gravelly
J
CL
may, shy may; silly day: lean day
fp
(Liquid Limit less than 50)
low
•�
OL
Organic silt; organic, silty clay of plasticity
w u 8
MH
Inorganic sift; micaoecus or diatomaceous fine sand
or I soil
tv `
LL a t
SILT AND CLAY
CH
Inorganic day of high plasticity; fat day
F
(Liquid Limit greater than 50)
MEOH
Organic day of medium to high plasticity; organic silt
HIGHLY ORGANIC SOIL
WE
PT
Peat; humus; swamp soil with high organic content
Notes: 1. (heal Iattk symbols 0.e., SM -5P) for a sand or gravel k dicwA a soll with an ostimaled S -t 5% lines. Multiple letter symbols (i.e.. ML/CL) indIcates
borderline Of ML49PIO soil dassilfcatlons. Only the lust tetter symbol's rospecdve pattern is shorn on logs. DemeP Han and IdwUNCE1tlon of SOU
2. Sal dasatptbns shorn an logs use the temrirsdogy and general approach fm the Vbual-ALvhra► Procedue.
as oullined In ASTM D 2486.
3. Sall desadptions (whlch are based on estimated values) are as Idlows: primary Soil Type(s) - Le.,'GRAVEL'.'SAND'.'SILT`, CLAY', etc.
secondary Soll Type(s) (:.16%) • i.e.. •gravotly'.'sandy. 'clayey'. etc.
Modif-ier(s) (a5% and Sts%) - I.e., -with graver.'sw4h sand',1Nith day', etc.
Mnor Component(s) (SS%) - i.e.. -trace graver.trace sand'.'Irace day', etc.
Soil Classification System
Attachment 1
n
Boling 1
Approximate Elevation 15 Feet
10.0-17.5 SP Gray, medium to coarse SAND with gravel 12.5-14.0 38
(medium dense to dense, wet)
17.5-19.0 GP Gray, fine to coarse GRAVEL with sand (dense to 17.5-19.0 52
very dense, wet)
Boring completed to 19.0 ft on 7115/91.
Groundwater encountered at time of drilling at 9.0 ft.
Boling 2
Approximate Elevation 15 Feet
Sou Sample Blows
Classification
Depth System Interval per
(feet) Symbol Description (feet)
2" asphalt
0.1-45
Soil
4.5-8.5
sample
Blows
ML/OL
Classification
SP
Interval
per
Foda)
Depth
(fast)
System
Symbol
Description
(feet)
2" asphalt
Medium brown and gray, fine to coarse SAN() wlth
2.5 X4.0
23
0.1-7.5
SM/GM
and silt, and fine to coarse GRAVEL with
gravel
sand and sift (medium dense, moist) (1III)
MUOL
Dark brown to medium gray -brown SILT with
7.5-9.0
1 for 18"
7.5-10.0
organics and reeds, and organic SILT (very soft,
moist)
10.0-17.5 SP Gray, medium to coarse SAND with gravel 12.5-14.0 38
(medium dense to dense, wet)
17.5-19.0 GP Gray, fine to coarse GRAVEL with sand (dense to 17.5-19.0 52
very dense, wet)
Boring completed to 19.0 ft on 7115/91.
Groundwater encountered at time of drilling at 9.0 ft.
Boling 2
Approximate Elevation 15 Feet
Sou Sample Blows
Classification
Depth System Interval per
(feet) Symbol Description (feet)
2" asphalt
0.1-45
SM/GM
4.5-8.5
OUPT
8.5-14.0
ML/OL
14.0-18.5
SP
Medium brown to gray, silty fine to coarse SAND
with gravel and silty fine to coarse GRAVEL with
sand (medium dense, moist to wet) (fill)
Dark brown to brown -black, organic SILT and
PEAT (very soft, moist)
Dark brown SILT with organics interlayered with
thin layers of gray, fine to coarse sand; sandier
towards base, gradational contact (very soft, moist)
Gray, medium to coarse SAND with gravel and
trace silt (medium dense, wet)
2.5-4.0 12
7.5-9.0 3 `
12.5-14.0 1 for 18"
17.5-19.0 21
18.5-225 SM Gray, silty, fine SAND with gravel (medium dense 21.0-225 40
to dense, moist) (till)
Boring completed to 225 ft on 7/15/91.
Groundwater encountered at time of drilling at 14.0 ft. .
(a) Blows required to drive 20 -Inch OD split -barrel sample 1 foot with a hammer weight of 140 pounds and
a stroke of 30 Inches.
LANDAU ASSOCIATES, INC.
Log of Borings
'^ 7 Attachment 2
Boring 3
Approximate Elevation /5 Feet
V
(a) Blows required to drive 2.0 -inch OD split -barrel sample 1 foot with a hammer weight of 140 pounds and a
stroke of 30 inches.
LANDAU ASSOCIATES, INC. Log of Borings J
8 Attachment 2
Son
Sample
Blows
Classification
Interval
per
Depth
System
(feet)
Footiel
(feet)
Symbol
Description
'
3',asphalt
SM/GM
Medium brown to gray, sihy, fine to coarse SAND
2•!�4b
8
0.24.5
with gravel and silty fine to coarse GRAVEL with
sand (loose, moist to wet) (fill)
4.5-9.5
MLIOL
Medium brown and dark brown SILT with organics,
7.5-9.0
3
twigs and reeds, and organic SILT (very soft to
soft, moist)
9.5-22.0
SW/GW
Dark gray, fine to coarse SAND with gravel and
GRAVEL with trace sift (dense
12.5-14.0
17.5-19.0
87
50 for 5.5'
sandy fine to coarse
to very dense, wet)
SP/SM
Gray, medium to coarse SAND with gravel grading
22.5-23.5
50 for 5'
22.0.23.0
to gray, fine to medium SAND with silt and gravel
(very dense, moist) (till)
Test pit completed to 23.0 it on 7/15191.
Groundwater encountered at time of drilling at 9.5 It.
V
(a) Blows required to drive 2.0 -inch OD split -barrel sample 1 foot with a hammer weight of 140 pounds and a
stroke of 30 inches.
LANDAU ASSOCIATES, INC. Log of Borings J
8 Attachment 2