Report •
observed the prepared lot subgrades on July 29, 2016; several soft areas were observed. On
August 8, 2016 we observed the soft areas had been repaired. On August 12, 2016 we observed
crushed rock subgrade for Lot 87 had been re-compacted.
Members of our geotechnical staff observed geotechnical-related tasks identified above on an
intermittent and on-call basis. The results of our site visits were summarized in daily field
reports, copies of which have been provided to Polygon Northwest, Pacific Community Design,
and members of the design and construction team.
To the extent observed, the construction outlined above for subgrade preparation of
Lots 87, 88, and 89 at the West River Terrace residential development has been completed in
general conformance with the intent of the project plans, specifications, and our geotechnical
recommendations. Geogrid reinforcement for the Lock+Load retaining walls extends into the lot
areas. Future excavations should be limited to not disrupt or damage the geogrid reinforcement.
Footings for the residences on all the lots at the site can be designed and constructed in
accordance with the following recommendations from our December 5, 2014 geotechnical
report.
Footings can be proportioned for an allowable soil bearing pressure of 2,000 pounds per square
foot. A higher value may be possible, depending on the grading plan. The allowable bearing
pressure is a net bearing pressure; the weight of the footing and overlying backfill can be
ignored in calculating footing size. The allowable bearing pressure applies to the total of dead
plus long-term live loads and may be doubled for short-term loads, such as those resulting from
wind or seismic forces. Continuous wall and spread footings should be at least 16 and 24 inches
wide, respectively. The bottom of exterior footings should be at least 18 inches below the lowest
adjacent final grade. The bottom of interior footings should be placed at least 12 inches below
the base of the floor slab.
For foundations designed in accordance with the recommendations provided above, total post-
construction settlement is expected to be less than 1 inch and differential settlement between
adjacent foundation elements is expected to be less than%2 inch, given the anticipated building
loads for wood-framed residences.
In wet weather, we recommend placing a sufficient amount of crushed rock(typically 2 to
4 inches)to prevent disturbance to the foundation subgrades. The contractor is responsible for
the construction sequencing and methodology for footing excavation and construction.
Consequently, the actual amount of rock placed to protect foundation subgrades from
disturbance in wet weather should be selected by the contractor. Rock used to protect the
subgrades during wet weather should cover the foundation-bearing surfaces and be compacted
until "well keyed." Any foundation subgrade soil that is disturbed should be removed prior to the
placement of crushed rock and/or pouring of the foundations.
Lateral loads on footings can be resisted by passive earth pressure on the sides of the structures
and by friction on the base of the footings. Our analysis indicates that the available passive earth
pressure for footings confined by structural fill, or footings constructed in direct contact with the
undisturbed native soil or structural fill, is 350 pounds per cubic foot(pcf). Typically, the
C DESIGN 2 Polygon-123-03:090816
"POLYGON AT WEST RIVER TERRACE"
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CITY OF TIGARD, WASHINGTON COUNTY, OREGON
SURVEYED JULY 22, 2016
PREPARED FOR:
POLYGON NORTHWEST COMPANY
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LOT VANCOUVER, WA. 98660
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c I, TRAVIS C. JANSEN, A REGISTERED PROFESSIONAL LAND SCALE
2 SURVEYOR IN THE STATE OF OREGON, HEREBY CERTIFY THAT 20 0 10 20
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9 TO THE FOUNDATION ENVELOPE FOR LOT 89 OF THE PLAT 1 INCH = 20 FEET
q OF "POLYGON AT WEST RIVER TERRACE".
s� DRAWN BY: 12 DATE: 7/22/16 PACIFIC COMMUNITY DESIGN
REVIEWED BY: TCJ DATE: 7/22/16
PLANNING - ENGINEERING - SURVEYING
z PROJECT NO.: 395-029
(503) 941-9484