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GeoPacific
Engineering,Inc.
Real-World Geotechnical Solutions
Investigation•Design•Construction Support
October 22, 2018
Project No. 15-3729
Matt McBride
Windwood Construction, Inc.
12655 SW North Dakota
Tigard, Oregon 97223
FOUNDATION SUBGRADE REVIEW
LOT 8 OLSON WOODS
TIGARD, OREGON
GeoPacific Engineering Inc. (GeoPacific) previouslyperformed 9 9 armed ageotechnical engineering
investigation
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investigation of the site and provided recommendations for site development. We also conducted
on-call density testing and construction observations services during site development. This letter
addresses the single-family home foundation subgrade on Lot 8. We understand that the proposed
building is a two-story home with a crawl space.
As part of this evaluation, GeoPacific visited the site last week to observe the subgrade foundation
preparation. At the time of our site visit, the foundation excavation was complete and extended 12
to 48 inches below existing ground surface. The foundation bearing soils generally consisted of
compacted fill which was evaluated with a %-inch soil probe. Probing efforts resulted in 2 to 6
inches penetrating into the subgrade soils, indicating stiff consistency. The layout of the lot is gently
sloping with both very stiff fill and stiff native soils exposed perimeter footing. Footing-to-wall and
footing-to-slope setbacks were evaluated and were not an issue.
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 %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
crawispaces 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 our visit is for observations of foundation
bearing conditions only. Appropriate design professionals should be consulted regarding
14835 SW 72nd Avenue Tel(503)598-8445
Portland,Oregon 97224 Fax(503)941-9281
GeoPacific Engineering, Inc.
Job No. 15-3729
Lot 8 Olson Woods
crawlspace ventilation, building material selection and mold prevention issues, which are outside
GeoPacific's area of expertise.
We have prepared this report for Windwood 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{30120]
James D. Imbrie, P.E.
Geotechnical Engineer