Loading...
Report (5) rws—raaI — Dol-7a )(5 Sk, i/ mAft-s-,. 9`,-- *4/ Enliaeering.Inc. Real-World Geotechnical Solutions Investigation•Design•Construction Support June 29, 2017 Project No. 15-3808 JT Roth Construction, Inc. c/o Mr. Tim Roth 12600 SW 72nd Avenue, Suite 200 Portland, Oregon 97223 Via email to: timrCc' ;jtrothinc.co Subject: GEOTECHNICAL OBSERVATION OF FOUNDATION EXCAVATION CORBIN ESTATES—LOT 9 TIGARD, OREGON GeoPacific Engineering, Inc. (GeoPacific) conducted on-call testing and construction observation services for the Corbin Estates development. This letter addresses the building pad subgrade for Lot 9. It is our understanding that the planned structure at Lot 9 will consist of a single-family residence utilizing conventional spread footings. GeoPacific visited the site June 9, 2017 to observe the subgrade soils following the foundation excavation for Lot 9. At the time of our site visit, the excavation was complete and extended 12 to 36 inches below the surrounding grade. The foundation bearing soils consisted of native silt soils, and engineered fill soils which were observed and density tested by GeoPacific during mass grading of the site. Probing efforts with a '/ inch steel hand probe indicated stiff consistency in the subgrade soils. The layout of Lot 9 slopes gently downward to the east, and the footing layout includes several steps. Footing-to-wall and footing-to-slope setbacks were not an issue. Based on observed conditions, the footing subgrade soils are considered suitable for foundation support. The foundation subgrade as prepared is considered suitable to support the planned allowable bearing pressure of 1,500 psf. Estimated settlement under the allowable bearing pressure is 1 inch total, and %-inch differential, measured over a horizontal distance of 20 feet. Care should be taken to avoid saturation or disturbance of footing subgrade soils during and after excavation. If footing bearing soils become saturated or disturbed, any softened soil or slough should be removed and replaced with crushed aggregate or additional concrete. In general, footing excavations should be cleaned such that no more than approximately Winch of loose soils are present prior to pouring concrete. 14835 SW 72"d Avenue .. . Portland, Oregon 97224 Tel(503)9 Fax(503)9448-921-928181 Corbin Estates—Lot 9 GeoPacific Project No. 15-3808 Construction should include typical measures for controlling subsurface water beneath the homes, including positive crawlspace drainage to an adequate low point drain exiting the foundation, visqueen covering the exposed ground in the crawlspace, and crawispace ventilation (foundation vents). The homebuyers should be informed and educated that some slow flowing water in the crawlspaces is considered normal and not necessarily detrimental to the home given these other design elements are incorporated into its construction. Appropriate design professionals should be consulted regarding crawispace ventilation, building material selection and mold prevention issues, which are outside GeoPacific's area of expertise. We have prepared this report for J.T. Roth Construction, and it should not be relied upon by third parties without consulting GeoPacific. Within the limitations of scope, schedule and budget, GeoPacific attempted to execute these services in accordance with generally accepted professional principles and practices in the fields of geotechnical engineering and engineering geology at the time the report was prepared. The conclusions and interpretations presented in this report should not be construed as a warranty of the subsurface conditions. No warranty, expressed or implied, is made. The scope of our work did not include flood hazard evaluations, environmental assessments, the presence or absence of wetlands; or potential hazardous substances in the soil, surface water, or groundwater at this site. We appreciate this opportunity to be of service. Sincerely, GEOPACIFIC ENGINEERING, INC. u PROp.. I- Ael ,AY,*t *fid `44'f# rA' lel ir rte: rz/I07 Benjamin G. Anderson, P.E. Project Engineer 15-3808,Corbin Estates—Lot 9 2 GEOPACIFIC ENGINEERING, INC.