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GeoPacific
Engineering,Inc.
Real-World Geotechnical Solutions
Investigation• Design•Construction Support
October 21, 2019
GeoPacific Project No. 15-4010
Riverside Homes, LLC
17933 NW Evergreen Parkway, Suite 370
Beaverton, OR 97006
Via email to Amo Avgi (aavgiAriversidehome.com)
Subject: GEOTECHNICAL OBSERVATION OF FOUNDATION SUBGRADE
ELDERBERRY RIDGE SUBDIVISION—LOT 14
TIGARD,OREGON
GeoPacific Engineering, Inc. (GeoPacific) conducted on-call density testing and construction
observation services for the Elderberry Ridge Subdivision site. This letter addresses the footing
subgrade conditions for Lot 14. It is our understanding that the planned structure will consist of
a single-family residence utilizing conventional spread footings.
GeoPacific personnel visited the site on October 1991, to observe subgrade soils during the
foundation excavation for Lot 14. The excavation depth was approximately 12 to 36 inches
below the surrounding grade. The foundation bearing soils consisted of engineered fill soils,
which were evaluated with a hand probe. Probing efforts stiff soils. The footing layout of Lot 14
and the adjacent lots is stepped on a 2H:1V slope. Footing-to-slope setbacks were adequate,
however, some structural backfilling in the interior of the foundation may be necessary to
support the vertical cuts.
Based on observed conditions, the footing subgrade soils are considered suitable for foundation
support. The foundation subgrade as prepared is 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 Y2-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 %-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 are incorporated into its construction. Appropriate
design professionals should be consulted regarding crawlspace ventilation, building material
selection and mold prevention issues, which are outside GeoPacific's area of expertise.
14835 SW 72nd Avenue Tel (503) 598-8445
Portland,Oregon 97224 Fax(503)941-9281
Elderberry Ridge - Lot 14
GeoPacific Project No. 15-4010
We have prepared this report for Riverside 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.
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EXPIRES:06/30/202j
James D. Imbrie, P.E., G.E., C.E.G.
Principal Geotechnical Engineer
2 GEOPACIFIC ENGINEERING, INC