Report Jun. 21. 2007 3:10PM // < -6000? 5 -,, No 1334 P. 1
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EnyincerinU, Inc.
Real -World Geotechnical Solutions
Investigation • Design • Construction Support
June 21, 2007
Project No. 02 -7801
Attention: Robert Nester
Riverside Homes, Inc.
1925 SW AmberGlen Parkway, Ste 200
Beaverton, OR 97006 •
Fax 503 -968 -9165
RE: SOIL ENGINEER'S REVIEW OF FOUNDATION EXCAVATION SUBGRADE
LOT 12 BELLA VISTA
TIGARD, OREGON
References:
1. GeoPacific Engineering Inc., Geotechnical Report, Bella Vista, Tigard, Oregon, dated
December 9, 2002:
2. GeoPacific Engineering Inc., Soil and Wall Engineer's Summary at Conclusion of
Earthwork, Bella Vista, Tigard, Oregon, June 15, 2005.
GeoPacific Engineer, Paul Rabay, visited the site to review the foundation excavation subgrade. To
our knowledge, no engineered fills were placed on the subject lot. Much of the foundation bottom
subgrade is hard rock, except the rear footing subgrade, which is very stiff native soil that could be
probed less than 2 inches using a steel "T" bar probe. The rear footing is within 2 feet of a vertical
cut up to 11.5 feet tall and portions of the east side footing is within a foot of a vertical cut up to 8
feet tall. Adequate setbacks have not been maintained. We recommend these cuts be backfilled
with 1W-0 compacted crushed rock at a 2H:1 V slope to provide support of the adjacent footings.
Rock backfill should be compacted in 12 inch lift to at least 95% of the maximum dry density
obtained by ASTM D698 or equivalent and rock placement and compaction should be observed by
GeoPacific. Rock backfill may take place after pouring foundations but should be completed prior to
house construction. Following the placement of compacted crushed rock, the observed subgrade
will be adequate for support to an allowable bearing pressure of 2,000 psf and a maximum column
load of 30 kips. For greater loads, the geotechnical engineer should be consulted.
Where stepped foundations are present, a 1H:1V setback should be maintained to avoid
surcharging of the lower foundation wall. Continuous horizontal steel reinforcing is recommended in
the stem wall and footing for stepped foundations.
The cut is very near an existing rock wall. If the cut is to be exposed for a long duration, we
recommend backfilling this area to prevent sloughing and damage to the wall.
The coefficient of friction between on -site soil and poured -in -place concrete may be taken as 0.40
with no factor of safety added. The maximum anticipated total and differential footing movements
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Jun. 21. 2007 3:10PM
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No. 1334 P. 2
'GEOPACIFIC ENGINEERING, INC.
Project No. 02 -7801
Bella Vista
(generally from soil expansion and /or settlement) are 1 inch and % inch, respectively, over a span of
20 feet.
Due to seepage observed near the northwest corner and west side of the foundation and low
permeability of on site soils, all foundations should incorporate appropriate drainage measures, The
uphill perimeter of footing should be provided with a drainage system as recommended in the above
referenced report. Also, crawispaces should be provided with a low -point drain and pass through
pipes should be installed through footings which would otherwise restrict water flow to the low -point
drain.
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 about Y2 inch of loose soils are present prior
to pouring concrete.
Our work scope pertains to a geotechnical engineer's foundation excavation review only and the
conditions existing and exposed at the time of our site visit. No warranty is herein expressed or
implied.
Sincerely,
GeoPacific Engineering, Inc.
Paul Rabay
Project Engineer
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