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GEDPRCIFIC
Real-World Geotechnical Solutions
Investigation•Design•Construction Support
November 1, 2021
Project No. 18-5046
David Weekly Homes
1905 NW 169th Place, Suite 102
Beaverton, Oregon 97006
Phone: 503-213-4408
Email: dmillermoylan(a�dwhomes.com
FOUNDATION SUBGRADE REVIEW
LOTS 5 AND 6—TRILLIUM HILL
TIGARD,OREGON
This letter addresses the single-family home foundation subgrades on Lots 5 and 6. We understand
that the proposed buildings are two-story, daylight basement homes with a crawl space. As part of
this evaluation, GeoPacific visited the site today to observe the subgrade foundation preparation. At
the time of our site visits, the foundation excavation was complete and extended approximately 6 to
48 inches below existing ground surface. The foundation bearing soils appeared to mostly consist of
medium stiff to stiff, native silt soils. Probing efforts with a 1/2-inch soil probe resulted in 1 to 12
inches of penetration into the subgrade fill indicating medium stiff to stiff consistency. The layout of
Lot 1 has slope descending toward the rear of the lot and may require some structural backfilling.
Footing-to-wall and footing-to-slope setbacks appeared to be adequate based on the anticipated
layout; however we believe the steps on a 2H:1V slope should have preferably been excavated
deeper into the slope by the excavator as we have previously requested.
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 3/4 inch differential, measured over a horizontal
distance of 20 feet; due to the shallow excavation depths, we anticipate that these settlements will
be realized. Some mucking on Lot 5 should be anticipated as it appears it has been open and
exposed to the elements for quite some duration.
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-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 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
Job No. 18-5046
Lot 5 and 6 Trillium Hill
crawlspace ventilation, building material selection and mold prevention issues, which are outside
GeoPacific's area of expertise.
We have prepared this report for David Weekly 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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OREGON
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EXPIRES:06/30/2023
James D. lmbrie, G.E.
Geotechnical Engineer