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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, Op PROpe 0 • 0 - r 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