HomeMy WebLinkAboutBuilding Correspondence 2013-7-9 Branch
E'N'GINEERING.=
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July9,2013 civil • transportation
structural • geotechnical
Mr.Derrick Westover S U R V E Y I N G
Bruce Wiechert Custom Homes,Inc.
3073 Skv iew lane 9
Eugene,Oregon 97405 Ol/ — 54e 7�.-3-0/37
RE: GAM-SPINE E LoopA7ION 0•/iO / `/�
GRA131DNE Loon (�/^
Lot 16 iMOUNTAN GATEWESISUBDIVISION( IV)
SPRINGFIELD,OREGON
BRANCH ENCLNEERING LTC.PROJECT No.13-o 17
July 8, 2013: A Branch Engineering, Inc.(BEI)geotechnical representative visited the above referenced
site to observe the building pad excavation, assess the shrink/swell potential of the subgrade soil, and
determine the bearing capacity of the final building pad grade for construction of a single-family residence.
At the time of the visit the building pad excavation had been completed. The subgrade soil had been
stock-piled adjacent to the building pad and consisted of brown silty clay with basalt boulders and broken
rock. 6-to 14-inches of crushed aggregate had been placed across the pad,leveled, and compacted. The
maximum thickness of crushed rock aggregate appeared to be along the eastern edge of the pad. Along the
southwest corner of the pad basalt boulders were visible protruding up to 6- inches above the leveled
crushed rock surface. Density tests with a nuclear densometer were performed at two locations in the
eastern portion of the building pad. The density test results showed relative compaction in excess of 95%
(AASHTO T-99)which is acceptable for single family residential home construction.
Should the boulders protruding above the crushed rock surface lie within the perimeter foundation footing
forms some additional re-bar may be placed to mitigate concrete cracks in the vicinity of the boulders.
Although the expected settlement of the crushed aggregate is less than lb'the exposed native basalt boulders
will likely not settle uniformly with the placed compacted aggregate and cracking over time may occur. The soil
subgrade is suitable for a conventional perimeter-style foundation,and an allowable soil bearing capacity of
1,500 psf. Differential settlements are expected to be less than 1/2-inch over a span of zo feet. Surface
drainage shall be conveyed to a suitable disposal area,and final perimeter landscape grades shall slope away
from the foundation and surface water not be allowed to pond adjacent to the foundation.
Sincerely,
Branch Engineering Inc,
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DREG
O Seo. 15. 1998 S.)
EXPIRES: 12/31/2013
Ronald J.Derrick,P.E.,G.E.
Principal Geotechnical Engineer
EUGENE-SPRINGFIELD SALEM-KEIZER
310 Sib Street,Springfield,OR 97477 I p: 541.746.0637 I vww.branchengineering.com