Report ler
;or7 5 J 4 z( Ct GeoPacific
�/J� ll Engineering,Inc.
j" % ,,20 -001`/ Real-World Geotechnical Solutions
Investigation•Design•Construction Support
July 27, 2020
GeoPacific Project No. 18-5063
David Weekley Homes
1905 NW 169th Place, Ste. 210
Beaverton, OR 97006
Email: kthompson(c�dwhomes.com
SUBJECT: SHALLOW FOUNDATION SUBGRADE PREPARATION
RIDGECREST FKA ERIKA COURT SUBDIVISION LOT 9
TIGARD, OREGON
This letter addresses the single-family home foundation subgrade on Lot 9 of the Erika Court
Subdivision. We understand that the proposed building is a two-story home with a crawl space.
As part of this evaluation, GeoPacific visited the site on July 27t1 and today to observe the
subgrade foundation preparation. At the time of our site visit, the foundation excavation
generally extended 6 to 36 inches below the ground surface. It was apparent that the rear 10±
feet of the home had previously been excavated and organic soils replaced one to three feet
thick. We requested that this material be removed from the foundation subgrade.
After the removal, the foundation bearing soils generally consisted of medium stiff to stiff
engineered fill soil. Probing efforts with a 3/8-inch soil probe generally resulted in 2 to 6 inches
of penetration into the subgrade soils. Footing-to-wall and footing-to-slope setbacks were
adequate. The layout of lot 8 and the surrounding lots is gently sloping, with a slight overall
slope down to the northeast. On lot 8 there are short steps in the excavation so the northeast
quarter of the house footprint is lower than the rest.
Based on observed conditions, foundation subgrades as prepared are considered suitable to
support the planned allowable bearing pressure of 1,500 psf. Estimated settlement under the
allowable bearing pressure is 1-inch total, and % inch differential, measured over a horizontal
distance of 20 feet.
Care should be taken to avoid saturation or disturbance of footing subgrade soils during and
after excavation. If footing bearing soils become saturated or disturbed, any softened soil or
slough should be removed and replaced with crushed aggregate or additional concrete. In
general, footing excavations should be cleaned such that no more than approximately 1/2--inch of
loose soils are present prior to pouring concrete.
Construction should include typical measures for controlling subsurface water beneath the
homes, including positive crawlspace drainage to an adequate low-point drain exiting the
foundation, visqueen covering the exposed ground in the crawlspace, and crawlspace
ventilation (foundation vents). The homebuyers should be informed and educated that some
slow flowing water in the crawlspaces is considered normal and not necessarily detrimental to
the home given these other design elements incorporated into its construction. Adequate
crawlspace drainage is not something that geotechnical consultants can verify; the purpose of
14835 SW 72"1 Avenue Tel (503)598-8445
Portland, Oregon 97224 Fax(503)941-9281
GEOPACIFIC ENGINEERING, INC.
Project No. 18-5063
Ericka Court Lot 9
our visit is for observations of foundation bearing conditions only. Appropriate design
professionals should be consulted regarding crawispace ventilation, building material selection
and mold prevention issues, which are outside GeoPacific's area of expertise.
We have prepared this report for David Weekley Homes, and it should not be relied upon by
third parties without consulting GeoPacific. Within the limitations of scope, schedule and
budget, GeoPacific attempted to execute these services in accordance with generally accepted
professional principles and practices in the fields of geotechnical engineering and engineering
geology at the time the report was prepared. The conclusions and interpretations presented in
this report should not be construed as a warranty of the subsurface conditions.
No warranty, expressed or implied, is made. The scope of our work did not include flood hazard
evaluations, environmental assessments, the presence or absence of wetlands; or potential
hazardous substances in the soil, surface water, or groundwater at this site.
We appreciate this opportunity to be of service.
Sincerely,
GEOPACIFIC ENGINEERING, INC.
14...
GREGG,
ES D.04
EXPIRES.06/30/2 21
James D. lmbrie, G.E.
Geotechnical Engineer
14835 SW 72nd Avenue Tel(503)598-8445
Portland,Oregon 97224 Fax(503)941-9281
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