HomeMy WebLinkAboutBuilding Correspondence 2014-3-21 •
(Rranch
• ENGINEERING= .
Since 1977 •
March 21, 2014 civil • transportation
structural - geotechnical
Mr. Derrick Westover • SURVEYING
Bruce Wiechert Custom Homes, Inc. •3073SkyviewLane / Ctrt+tY 4
Eugene, Oregon 97405 .0I( _ Ai 2 y
RE: BUILDING PAD SUBGRADE EVALUATION
6193 GRAYSTONE LOOP
MOUNTAIN GATE WEST SUBDIVISION(PHASE IV)
SPRINGFIELD,OREGON
BRANCH ENGINEERING INC PROJECT No.13-017
A geotechnical engineer visited the above referenced site,on March 5, 12 and 19, 2014 to observe the
building pad excavation and 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 April 5, 2004 by Boire Associates Inc. indicates that this lot would not be graded; however,
subsequent reports by PSI and K&A Engineering indicate that the lot contained fill material near the
street. Initial test pits showed that the front portion of the pad had previously been filled with
unsuitable large stone and very moist clay. The rearlof the pad consisted of about 24-inches of
topsoil over stiff residual basalt soil near the base of the 3H:1V slope that rises to the west.
Perimeter cuts ranged from 3- to 6-feet to remove topsoil and fill material. The two-tier pad was
constructed atop native subgrade using compacted 3"-0 stone and 3A"-0 crushed aggregate with a 30-
inch step between tiers. The fill has been compacted structural standards of at least 90% of the
materials maximum dry density. Testing of the subgrade soil indicated a low to moderate
shrink/swell potential (IS 2720 result of 25%), which is mitigated by the stone/aggregate cover.
There is indication of slope instability or gross land morement on or in the vicinity of the site and .
no other geologic/geotechnical factors will impede site development as planned. The subgrade and
stone/aggregate fill is suitable for a conventional perimeter-style foundation, and an allowable soil
bearing capacity of 2,000 psf. Differential settlements are expected to be less than 1/4-inch over a
span of 20 feet. Footing drains are recommended for the site due to the slope at the rear of the pad.
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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PROFFS
4 S 01 N4'4 r4
OREGON
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EXPIRES: DECEMBER 31, 2015
Ronald J. Derrick, P.E., G.E.
Principal Geotechnical Engineer
EUGENE-SPRINGFIELD SALEM-KEIZER
310 51h Street,Springfield,OR 97477 I p: 541.746.0637 I www.branchengineering.com