Report -Nov. 9. 2006 12:38PM M5 r_20 40 - 602 8/ UCH io »U r. i
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GeoPrifit
Engineering, Inc.
Real -World Geotechnical Solutions
Investigation • Design • Construction Support
January 26, 2005
Job No. 04 -9001
Pays Custom Homes, Inc.
17481 SW Hoodoo Ci
Beaverton, OR 97007
Fax 503 -214 -8500
RE: SOIL ENGINEER'S SUMMARY AT CONCLUSION OF EARTHWORK
FEHRENBACHER SUBDIVISION
CITY OF TIGARD, OREGON
GeoPacific Engineering, Inc. recently completed on -call testing and construction observation services
for the above - referenced residential subdivision during the development construction portion of the
project. The purpose of this report is to provide a summary of the information generated from our
services and to make general conclusions regarding the suitability of the site for single - family home
development. This report does not supersede any actual soil observations made during single - family
home construction.
SITE PREPARATIOI I AND FILL PLACEMENT
Based on our site ob eervations during construction, no engineered fill was placed on the lots,
BUILDING EXCAVATION AND RECOMMENDED ENGINEERING REVIEW
No more than one foot of uncompacted fill should have been placed on level areas. Based on hand
probing, we anticipate 12 to 24 inches of excavation will be required to reach bearing soils.
Foundation excavations should be carried through any rain - softened fill or loosely compacted excess
soils placed over the surface of the lots, and any soft or organic native soils. For foundation
excavations performed during the wet weather season, we expect that additional excavation of 6
inches and placement of a thin layer of compacted rock fill will likely be necessary for improved spread
foundation support and protection of the subgrade.
FOUNDATIONS
No geotechnical investigation has been performed on the lots- and the site has been previously
developed. One area of buried debris was removed within the street; however shallow, conventional
isolated or continuous spread footings will likely be appropriate to support the proposed structures,
provided they are founded on competent native soils. We recommend a maximum allowable
bearing pressure of 1,500 pounds per square foot (psf) for designing the footings. A maximum
column load of 30 kips is recommended, subject to a geotechnical engineers review. For heavier
loads or any masonry walls or chimneys, the geotechnical engineer should be consulted. The
recommended maximum allowable bearing pressure may be increased by 1/3 for short -term
transient conditions such as wind and seismic loading. All footings should be founded at least 12
inches below the lowest adjacent finished grade. Minimum footing widths should be determined by
the project engineer /architect in accordance with applicable design codes. We recommend
minimum footing reinforcement of two No. 4 bars in the footing and one in the stem wall.
7312 SW Durham Road Tel (503) 598 -8445
Portland, Oregon 97224 Fax (503) 598 -8705
.Nov. 9. 2006 12:38PM uc. ibuu r.
Project No. 04-9001
Fehrenbacher Subdivision
Assuming construction is accomplished as recommended herein, and for the foundation loads
anticipated, we estimate total settlement of spread foundations of less than about 1 inch and
differential settlement between two adjacent load- bearing components supported on competent soil
of less than about 3 4 inch. We anticipate that the majority of the estimated settlement will occur
during construction, as loads are applied.
Wind, earthquakes, and unbalanced earth loads will subject the proposed structure to lateral forces.
Lateral forces on a structure will be resisted by a combination of sliding resistance of its base or
footing on the underlying soil and passive earth pressure against the buried portions of the structure.
For use in design, a coefficient of friction of 0.35 may be assumed along the interface between the
base of the footing and subgrade soils. Passive earth pressure for buried portions of structures may
be calculated using a equivalent fluid weight of 400 pounds per cubic foot (pcf), assuming footings
are cast against dens, natural soils or engineered fill. The recommended coefficient of friction and
passive earth pressure values do not include a safety factor. The upper one foot of soil should be
neglected in passive pressure computations unless it is protected by pavement or slabs on grade.
All footing excavations;; should be trimmed neat and the bottom of the excavation should be carefully
prepared. Loose or Softened soil should be removed from the footing excavation prior to placing
reinforcing steel bars. Excavations near structural footings should not extend within a 1H:1V plane
projected downward f the bottom edge of footings.
If footing excavations are open during the winter season or periods of wet weather, it may be helpful
to provide a layer of gushed aggregate to help preserve the subgrade until the footings are cast.
Crushed aggregate should consist of 1 — 0 crushed aggregate per the Oregon Department of
Transportation (ODOT) Standard Specifications.
ROADS, UTILITY TRENCHES
GeoPacific performed periodic testing of roadway fill and trench backfills during placement of the
water line, and sanitary sewer. Density test results generally indicate that backfill and base rock
tested were compacted in accordance with our recommendations and county standards (See the
attached Summary of Field Soil Density Tests). Asphaltic concrete density tests are also attached.
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Nov. 9. 2006 12:38PM No. /biiu r. i
Project No. 04 -9001
Fehrenbacher Subdiylsion
CLOSING AND LIMITATIONS
Our reports pertain t� the materials and locations tested /inspected only. This letter should be made
available to each housebuilder in the development. This letter should not be construed to relieve or
lessen the responsibility of the earthwork contractor or owner for site work, but is provided to meet
the minimum required governmental assurance in accordance with local engineering standards of
practice. Our services were provided on an as- requested basis. If conditions are encountered
during foundation ejccavation, which differ from this report, then the developer, the earthwork
contractor, and GeoPacific should be allowed to review the condition before corrective action is
taken. Corrective Work performed by the builder without notification of the above parties will be
considered as an acceptance of the conditions encountered. It is the housebuilder's responsibility to
educate homeowners for reasonable expectations on foundation performance and standard levels of
acceptable concrete cracking and crawispace drainage.
Sincerely,
GeoPacific Engineering, Inc.
R or
eik.Glri.EeD '
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James D. Imbrie, P. ., C.E.G.
Geotechnical Engin - er
Attachments: Site Plan
Field Soil Inspection Summary
Sum of Field Soil Density Tests
Summary of Field Asphaltic Concrete Density Tests
cc: AEI Community Development
Washington County
Revcon
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