HomeMy WebLinkAboutBuilding Correspondence 2013-6-17 r,
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Since 1977
June 17, 2013 civil • transportation
structural • geotech nica I
S U R-Y E-V I N G
Mr.Derrick Westover
Bruce Wiechert Custom Homes,Inc.
3073 Skyview Lane
Eugene, Oregon 97405
RE: SUBGRADE EVALUATION
6068 GRAYSTONE LOOP
LOTS MOUNTAIN GATE WEST SUBDIVISION(PHASE IV)
SPRINGFID.D,OREGON
BaA.xar Fl MEERING Ixc.Paolrcr No.13-017
June 11, 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. The pad was in the process of being excavated into a hillside sloping
downhill from south to north. The subsurface conditions consisted of a topsoil/organic zone
underneath a layer of silty clay fill with some rock. Beneath the topsoil zone a subgrade material
consisting of moist, brown to light brown clayey silt with a trace of fine grained sand was
exposed. The material appeared to be consistent and was medium stiff to hand probing. The
2004 Geotechnical Investigation Report by Boire Associates Inc. was consulted and the fill
overlying the topsoil/organics was found to be undocumented. BEI recommended that the
undocumented fill be removed as well as the underlying old topsoil/organics layer to expose a -
consistent clayey silt native subgrade. The subgrade shall be covered with a minimum of 6-
inches of compacted aggregate.
June 13, 2013: A BEI geotechnical representative returned to the above referenced site to observe
the compacted aggregate fill placement and to perform density tests with a nuclear densometer
(ASTDl D-1557). The final building pad subgrade consisted of two tiers of different elevation with
the upper tier lying on the south side of the building pad and extending the upper elevation to the
north along the west side of the pad. The lower elevation area of the building subgrade lies along
the north and east sides of the building pad. The subgrade material was covered in compacted
aggregate with fill thicknesses appearing to range from 8-inches to more than 30-inches. Density
tests with a nuclear densometer were performed and the results are summarized below. An
AASHTO T-99 Standard Proctor curve dated 1/25/2013 was provided to BEI for the W-0
compacted aggregate placed on the building subgrade. The uncorrected maximum dry density is
123.7 pcf at an optimum moisture content of 13.9%.
Dry Density Moisture Content Relative Compaction
Test Location (pcf) 05) T-99 (%)
Northwest Corner(upper tier) 134.1 6.1 100+
Southwest Corner(upper tier) 137.4 7.5 100+
Southeast Corner(upper tier) 133.0 6.2 100+
Northeast area(lower tier) 142.1 8.0 100+
Table 1: Density Test Results
The soil subgrade is suitable for a conventional perimeter-style foundation,and an allowable soil
bearing capacity of 1,500 psi. We recommend that the foundation perimeter be backfilled and
graded to slope away from the structure as soon as concrete curing allows. Differential settlements
EUGENE-SPRINGFIELD SALEM-KEIZER
310 Ph Street,Springfield,OR 97477 I p: 541.746.0637 I www.branchengineering.com
•
6068 Graystone Loop
June 17, 2013
are expected to be less than 1/2-inch over a span of 20 feet. Footing drains are recommended as the
subject lot lies below the adjacent street and may receive runoff from impervious surfaces to the
south or adjacent lots. 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,
_nFp PROF&_
I.GC 04GINEF9 0
- 16170 `
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2410 J. GE�P
EXPIRES: 12/31/2013
Ronald J.Derrick,P.E., G.E.
Principal Geotechnical Engineer
Branch Engineering, Inc.