HomeMy WebLinkAboutBuilding Correspondence 2013-6-12 ® anch
June12, 2013 ENGINEERING-
Since 1977
Mr.Derrick Westover civil • transportation
Bruce Wiechert Custom Homes,Inc. structural
geotechnical
3073 Skvwiew Lane su RVEVINC
Eugene,Oregon 97405
RE: SUBGRADE EVALUATION
838 MOUNTAINGATE DRIVE
LOT 100 MOUNTAIN GATE WEST SUBDIVISION(PHASE IV)
SPRINGFIELD,OREGON
BRANCH ENGINEERING INC.PROJECT No.13.017
A Branch Engineering,Inc. geotechnical representative has visited the above referenced site on June 11,
2013 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. The pad was excavated into a south facing slope with three-tiers. The largest and highest of
the tiers ran from the northern boundary of the pad south to the approximate edge of the driveway
access to the site. Below the main tier there were two tiers, each dropping in elevation approximately
12-inches. Along the northern building pad boundary a rockery retaining wall was constructed. Basalt
boulders were present in spoil piles and stockpiled adjacent to the site. The different subgrade tiers
were covered with compacted aggregate and leveled. Compacted aggregate thickness varied across the
site from as little as 2-inches along the cut in the northern portion to 6-inches along the front of the
northern tier. Along the southern boundary compacted aggregate thickness varied from 8-to 18-
inches to create a level building pad on the existing hillside. A smooth drum roller was used to
compact the aggregate,which is mechanically estimated to be at least 95% of the materials maximum
dry density. The 2004 Geotechnical Investigation report by Boire Associates Inc.indicates that Lot 100
is a fill lot comprised of miscellaneous stone embankment and are suitable for conventional foundation
systems with no slope stability issues.
The soil subgrade is suitable for a conventional perimeter-style foundation,and an allowable soil
bearing capacity of 1,500 psf. We recommend that the foundation perimeter be backfilled and graded
to slope away from the structure as soon as concrete curing allows. Differential settlements are
expected to be less than 1/2-inch over a span of 20 feet. Footing drains are not required as the subject
and adjacent lots area relatively flat. 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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OREGON
ST 15,�°�
Ronald J.Derrick,P.E., G.E. Expires 12/31/2013
Principal Geotechnical Engineer
EOCENE-SPRINGFIELD SALEM-KEIZER
310 5th Street,Springfield,OR 97477 I p: 541.746.0637 I iwrw.branchengineering.com