Report 5rr97 - 0001 g
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BRAUN' Braun Intertec Corporation
6032 N. Cutter Circle, Ste. 480
INTERTEC P.O. Box 17126
Portland, Oregon 97217
503- 289 -1778 Fax: 289 -1918
Engineers and Scientists Serving
the Built and Natural Environments
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' May 12, 1997 Project No. EAAX -97 -0397
Report No. 09- 057 -2976
Mrs. Betty Sarich
1 12860 S.W. 135th Avenue
Tigard, Oregon 97223
Dear Mrs. Sarich:
' Re: Site Reconnaissance, Single Family Residential Lot,
12810 S.W. 135th Avenue, Tigard, Oregon
At your request, we have looked at the site proposed for the construction of a single - family
dwelling at the referenced location in Tigard, Oregon. This is a report of our findings,
' conclusions and recommendations.
I Scope of Services •
The writer, a Senior Engineer with our firm, visited the site on May 7, 1997. Visual
observations of the slopes, vegetation, surface drainage and exposed soils and rock were made.
' Our reconnaiss -ance did not include soil'borings or rock coring to explore the soil, rock and
groundwater conditions at depth, nor did it consider the effect of a major earthquake. The
conclusions and recommendations are based solely on our visual observations of the site, and
' our familiarity with soils, geology and construction practices in the area. Borings or test pits to
better explore the subsurface conditions can be provided at additional cost.
Site Description
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The proposed site measures approximately 59 feet along S.W. 135th Avenue by 187 feet in
depth. It consists of a nearly level area within the building pad area. The site then slopes into a
ravine at the back of the lot.
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' Mrs. Betty Sarich
Project No. EAAX -97 -0397
' Report No. 09- 057 -2976
May 12, 1997
Page 2
Soils and Geology
Soil exposures in the area consist of silt, a structureless brown to yellowish -brown mottled
clayey to sandy silt. The underlying geologic unit consists of bedrock of volcanic origin.
' Bedrock is not exposed in the immediate area but is believed to underlie the project site at a
depth of several tens of feet.
No evidence of unstable soil or recent soil movements were observed in the slope or in the
immediate vicinity of the project, nor was evidence of groundwater (springs or seeps)
' encountered.
Proposed Construction
We understand the proposed construction will consist of a single - family dwelling with a garage
constructed near the level of the street.
111 Conclusions and Recommendations
The site appears stable and it may be developed for residential purposes provided the following
' recommendations and precautions are 'incorporated into the construction.
' The structures may be supported on native soils or engineered clean granular fill, crushed rock
or lean concrete using spread footings. Spread footings may be designed for maximum contact
pressures of 2,000 psf, with a minimum footing width of 16 inches. The footings should be at
least 12 inches below the exterior finished grade to provide frost protection.
Lateral earth pressures on walls which are not restrained at the top, such as retaining walls, etc.,
may be calculated on the basis of an equivalent fluid pressure of 35 pounds per cubic foot (pct)
' for level backfill and 60 pcf for steeply sloping backfill. Walls that are restrained from yielding
at the top may be calculated on the basis of an equivalent fluid pressure of 55 pcf for level
backfill and 90 pcf for steeply sloping backfill. Lateral loads, may be resisted by passive
pressures acting against footings and by frictional resistance between foundation elements and
supporting soils. An equivalent fluid density of 300 pounds per cubic foot (pct) and a friction
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Mrs. Betty Sarich
Project No. EAAX -97 -0397
Report No. 09- 057 -2976
' May 12, 1997
Page 3
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factor of 0.3 may be used for design for foundations bearing on and resisted by native soils.
' The recommended equivalent fluid density includes a factor of safety of 1.5 which is appropriate
due to the amount of movement required to develop full passive resistance.
' All backfill for retaining walls, foundation walls, etc., should be select granular material (sand
and /or sandy gravel). We anticipate that on site material will not be suitable for this purpose
' and that it will be necessary to import material to the project for structure backfill. Native
material can be used for the last 18 to 24 inches of the fill, thus acting as a seal to the granular
fill.
Temporary earth slopes may be cut near - vertical to a height of 4 feet, above which flatter slopes
will be required.
An adequate subsurface drain system should be installed behind subsurface walls such as
' retaining walls, foundation walls, etc. All structures having a crawl space should he provided
with a low point crawl space drain. Surface run -off drains and the subsurface drains should be
carried to the storm sewer or other approved discharge areas.
Foundation Preparation.
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Inasmuch as the soil units which will provide support for the main structure are extremely
' sensitive to disturbance in the presence of excess moisture, care should be taken to protect
prepared bearing surfaces until footing concrete can be placed. Precautions to achieve this end
would consist of (1) covering of prepared bearing surfaces with impervious membranes or
granular blanket (4 -inch maximum thickness) or (2) cessation of work during rainy weather.
Under no circumstances should fills be constructed anywhere on the slope. Surplus material
(other than the small amount to be removed from local excavations) must he removed from the
site to a remote disposal area.
All roof, yard, and other upland surface water must be directed to storm sewers or other
approved discharge points.
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