Report Fax :5032232630 Oct 30 '98 14 32 P. 02
•'�- = AseIRp
�.. ar I soTestin O. Bax 3sta
��chmice
, and o 4080 HUW,lsu 3 Ave., NE
Inc. • �� Ph 684-3460
F AX ( 8 4 Salem 0 97301
Pibt1R (a 03' S92•1262
FAX ( 3) 3861308
October 21, 1894
CTI #98-G1767
GFC General Contracting
17017 Cana/ Circle
Lake Oswego, OR 97035
DI8CUS8IO111 OF LIQUEFACTION POTENTIAL AND SOIL STRENGTH LOSS
PACIFIC UTILITY TRAILER BUILDING ADDITION - HUNZIKER ROAD
T1GARD, OREGON
Pursuant to your request, an engineer from Carlson Testing, Inc. (CTII has reviewed the .;it
and proposed construction with regards to reviewing the dynamic soil response during seis ni
events. The proposed construction is a single -story, steel framed bu ?din with thickened 9 h a concr
Slab-on-grade, hickened footings around three sides, and a Sto 9 foot tall cantilever concret)
retaining wall along the back side.
• The primary purpose of this letter is to address the soil liquefaction hazard, its potert:ie I
detrimental effects on the structure, end to present recommended mitigating measures. - "h 3
site is underlain by fine - grained slit soils classified as ancient flood deposits (Off). Based 011
the DOGAMI Open File Report No. 0 -90 -2, the site is underlain by about 60 feet of Off ave
400 feet of very stiff undifferentiated Iacustrine sediments over basement rock coneietin(i of
Columbia River Basalt. Rased on our extensive experience with nearby sites containing
ancient flood deposits, the Off has a high potential for liquefaction generally at a depth of
about 10 to 20 feet below original grade during a very large seismic event (0.34g PGA fen en
event recurrence interval every one thousand years ova 5% chance of occurrence in next 51
years). For the code required design event which has PGA of 0.249 and a recurrence irate, ve I
of every 500 years or a 10% chance of occurrence in the next 50 years, the potential for
damaging liquefaction is only considered low to moderate.
If liquefaction should occur, we do not expect a significant loss of bearing strength within tho
Zone of influence beneath the spread foundations, nor do we expect that significant lat:irg 1
spreading would occur. Seismic induced settlement is estimated to range between one to
three inches. Given the type of structure, although the estimated settlements could ca 3si3
significant damage to the structure, the effective hazard to occupants is considered minis eel.
To mitigate seismic induced settlement, after performing deep subsurface explorations, auc'ar
cast piles could be drilled to a depth below any expected liquefiable layers. This wouh
mitigate settlement below the foundations, but not beneath the stab - grade. The projec tee)
extra costs for design and construction are estimated to be between 430,000 to $50,0 70.
The decision to mitigate against liquefaction is the responsibility of ti owner.
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Fax :5032232630 . Oct 30 '98 14 33 P. 03
#98 - 01757
Page .2of2
This letter is based on our best understanding of the types of deposits at the site and state .01-
the-art evaluation of dynamic behaviors of silts. No deep detailed investigations v er a
performed specifically at the site. Information contained" herein is not to be reproduced,
except in full, without prior authorization from this office. if there ere any further questions;
regarding seismic hazards, please do not hesitate to contact this office.
Respec • I fitted,
s
-0 ..
14743
/` .. OREGON
v 4 • 23 ��� F,
'°IF �. 1@f►���
James D. Im •rie, P.E.; C.E.G.
Principal Engineer
Main Office Branch Office
P.O. Box 23814 4060 Hudson Ave., NE
Tigard, Oregon 97281 Salem, OR 97301
Carlson Testing, Inc. Phone (503) 684 -3460 Phone (503) 589 -1252
FAX (503) 684 -0954 FAX (503) 589 -1309
September 10, 1998
CTI #98 -G1757
GFC General Contracting
17017 Canal Circle
Lake Oswego, OR 97035
GEOTECHNICAL REVIEW FOR RETAINING WALL CONSTRUCTION
PACIFIC UTILITY TRAILER BUILDING ADDITION - HUNZIKER ROAD
• "- TIGARD, OREGON
Pursuant to your request, an engineer from Carlson Testing, Inc. (CTI) has visited the above
referenced building addition with regards to reviewing the soil conditions for the proposed
{ ' S A
construction of a 6 to 9 foot tall cantilever concrete retaining wall that will be a part of the
warehouse -type building wall on the east end of the property. The purpose of our review was
to note the soil conditions and provide recommendations for design of this new wall.
The existing soil conditions exposed in the cut were fine grained flood deposits (brown SILT)
that are typical of the Portland area. The central portion of the cut was wet and has softened
because the silt has no clay and the groundwater seepage is causing the soil grains to
essentially float.
We recommend that the center 75 feet be overexcavated a depth of 2 feet and backfilled
immediately with one foot of 1 crushed drain rock and one foot 11/2"-0 crushed
"4- aggregate base rock compacted to at least 90 percent of the modified Proctor maximum dry
density. Replacement with compacted gravel should be performed quickly so that the weight
of the gravel is in place before the soil is allowed to soften. Once the overexcavation work
is performed, the allowable bearing at the base of the wall is 2,000 Ib /ft The equivalent -fluid
active pressure for a well drained wall is estimated at 55 Ib /ft
G o
The coefficient of friction between soil and concrete may be taken as 0.35; however we
(^ 'i suggested placing at least a 4 -inch thick layer of lightly compacted 1 %2 " - crushed aggregate
base over the subgrade even in areas not recommended for overexcavation. This should
improve the coefficient of friction to at least 0.48. Passive resistance may be assumed at 300
Ib /ft
Information contained herein is not to be reproduced, except in full, without prior authorization
..: from this office. If there are any further questions regarding this matter, please do not hesitate
to contact this office.
� �Ep PROF
Respectfully submitted, � F- SS
. ; CARLSON TESTING, INC. �5 �iGI �o ,�
`4y • �� 14743 9 <
•
4� OREGON
• James D. Imbrie, P.E., C. e. v.Q g0
Principal Engineer vq 23• \c5
� _ I FS D. t•B` EX- 3a -