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HomeMy WebLinkAboutBuilding Correspondence 2013-9-19 I `q �� �/�p an mY , E GINEERING_ September 19,2013 Since 1777 'culls taia:n?Portarfanl Mt Derrick Westover strurturaI A.,:9Potechni[P , 5 1sRV �Y N G"r== • Bruce Wiechert Custom Homes,Inc. ' 3073 Skyview Lane Eugene,O egon 97405 +41 RE: SUBGRADE EVALUATION . ;--.. • 6231 GRAYSfOWE LOOP • . Len-63 MOUNTAIN GATE WEST SUBDIVISION(Pnast IV) . • SPRINGFIELD;OREGON • BRaNcu ENGINEERING Ivc.PRninrr No.13-0r7 September 12, 2oRjh 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 the suitability for placement of fill for the construction of a level building pad. The site is situated on a slope falling from the north side of the site to the south_ At the time of the visit the topsoil and near surface soil had been removed. A moist brown silty clay subgrade was exposed. In the areas of trees that were previously on the site over-excavation had taken place to remove soft soils and organics. The subgrade soil was medium stiff when probed with a steel hand probe. Cuts along the uphill (northern)boundary of the building pad area were approximately 4-feet in height and decreased to approximately 1.5 to 2-feet in height along the lower(southerly)portion of the pad area Rocky fill consisting of basalt boulders up to 12- inches in diameter mixed with smaller sized rocks and silty clay was being placed on the southerly half ''of the pad.and walked into place in lifts with a metal tracked excavator. September 16, 2013: The geotechnical engineer of record and a BEI geoterhnical representative visited the site to document the cons truction progress of the building pad. The placement of the fill material consisting of basalt rocks with silty clay had been completed and a level subgrade surface for placement of aggregate fill had been constructed. At the time of the visit processed aggregate 1 W"-(o)in size mixed with clay was being imported to the site,placed in lifts and compacted with a single smooth drum roller. r , September 18, 2013: A BEI geotechnical repmsentativeiisited the site to document the construction of the building pad and to monitor proof rolls conducted on the compacted aggregate fill with a fully loaded to . A. CY dump truck. The completed building pad consists of two level.benches stepped into the existing hillside sloping from north to south. Fill thickness of the compacted aggregate with clay on the upper(northern) bench varies from 4 to 6- inches along the upslope side and increases to more than z4- inches along southern edge of the upper tier. Fill thickness on the lower(southern)bench consists of 6 to 12-inches of compacted aggregate along the western portion of the pad and increases along the eastern edge of the pad to approximately 24-inches along the western limit"of the pad! A proof roll with a fully loaded to CY dump truck across the pad was conducted. Minimal amounts of deflection at the surface of the pad were observed • under load. • • t The soil subgrade is suitable for a conventional, foundation,and an allowable soil bearing capacity of 1,5oo psi'. Low to moderate"shiink swell potential of the native subgrade soil shall be mitigated by the placement of compacted aggregate: 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 zo feet. Footing drains are recommended as the subject lot lies below adjacent properties. Surface drainage shall be conveyed to a suitable disposal area and final perimeter landscape grades shall slope away from the foundation. Surface water shall not be allowed to pond adjacent to the foundation. J s.. EUGENE-SrRINGGE1D SALEM-KEIZER ,- e_A - 310 5th Street,Springfield,OR 97477 'I p:541.746.0637, I www.branchengineering.com • I ` 6231 Graystone Loop September 19, 2013 Sincerely, Branch Engineering Inc, PRO, ��GI NEF9�1�0 #16170P 13 OREGON r amp- 15,199Y IN.�� EXPIRES: 12/31/2013 Ronald S. Derrick, Principal Geofec:nical Engineer Branch Engineering,inc.