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GEOPPCIFIC
Real-World Geotechnical Solutions
Investigation • Design • Construction Support
August 3, 2023
Project No. 22-6162
Ichijo USA Co., LTD
Attn: Erik Gomez
1509 SW Sunset Blvd. Suite 2-D
Portland, Oregon 97239
Via email to: erik.gomeznichijousa.com
FOUNDATION SUBGRADE REVIEW
LOT 122 RIVER TERRACE CROSSING AKA CROSSING AT BULL MOUNTAIN
15819 SW BLUEWATER TERRACE
TIGARD, OREGON
This letter addresses the single-family home foundation subgrade on Lot 122 of the River Terrace
Crossing development, also known as Crossing at Bull Mountain. We understand that the proposed
building is a two-story home with a stepped foundation for a tall crawlspace. As part of this evaluation,
GeoPacific visited the site on July 25, 2023.
The excavation on lot 122 is stepped down in several benches, with a depth of up to 4 feet below
surrounding grades. The tallest bench was about 3 feet tall.
The exposed subgrade on lot 122 appeared to consist of fill material placed during mass grading of
the subdivision. The subgrade at the rear footing appeared to consist of silty gravel and cobbles,
while the subgrade on the benches and at street level appeared to consist of silt.
The foundation layout of Lot 122 is stepped down to the west. Footing-to-slope and footing-to-wall
setbacks did not appear to be an issue for the structure. Since the subgrade at the rear footing
consists of very dense rocky fill and the slopes are not graded at 50 percent below the house, a
reduced footing-to-slope setback distance was allowed. Grades to the west are approximately 25
percent, and the footing to slope distance is approximately 3 feet. The rear footing of the house
generally appeared to have adequate slope setback distance.
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. Also, crushed rock placed over the surface of the subgrade should
14835 SW 72"d Avenue Tel (503) 598-8445
Portland, Oregon 97224 Fax(503) 941-9281
GeoPacific Engineering, Inc.
Job No. 22-6162
Lot 122 River Terrace Crossing
be compacted so that no more than approximately '/-inch of loose gravel is 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
crawlspace ventilation, building material selection and mold prevention issues, which are outside
GeoPacific's area of expertise.
We have prepared this report for Ichijo USA, 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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Benjamin G. Anderson, P.E.
Associate Engineer