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Report GeoPacific Engineering,Inc. Real-World Geotechnical Solutions Investigation•Design•Construction Support February 21, 2020 Project No. 18-4824 ('' i2.0 1' . Stonebridge Job No. 2755 Stonebridge Homes NW LLC n(1 4 >2 Andy Thomas 4230 SW Galewood St., Ste. 100 Lake Oswego, OR 97035 Fax 503-387-7615 Email: AndvAstonebridgehomesnw.com; JimD(a�stonebridoehomesnw.com; tianar(a?_stonebridge- realty.com FOUNDATION SUBGRADE REVIEW LOT 1— BRIGHTWOOD SUBDIVISION 11349 SW ELLSON LANE TIGARD, OREGON GeoPacific Engineering Inc. (GeoPacific) previously performed a geotechnical engineering investigation of the site and provided recommendations for site development. We also conducted on-call density testing and construction observations services during site development. This letter addresses the single-family home foundation subgrade on Lot 1. We understand that the proposed building is a two-story home with a crawl space. As part of this evaluation, GeoPacific visited the site this week to observe the subgrade foundation preparation. At the time of our site visit, the foundation excavation was complete and extended about 12 to 24 inches below existing ground surface. The foundation bearing soils generally consisted of medium stiff, native soils. Probing efforts with a %-inch soil probe resulted in 6 to 24 inches of penetration into the subgrade soils, indicating medium stiff consistency. The layout of Lot 1 is mostly flat. Footing-to-wall and footing-to-slope setbacks were not an issue. Based on observed conditions, foundation subgrades as prepared are 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 '%-inch of loose soils are present prior to pouring concrete. 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 crawlspace ventilation (foundation 14835 SW 72nd Avenue Tel(503)598-8445 Portland,Oregon 97224 Fax(503)941-9281 • GeoPacific Engineering, Inc. Job No. 18-4824 Lot 1 Brightwood vents). The homebuyers should be informed and educated that some slow flowing water in the crawispaces is considered normal and not necessarily detrimental to the home given these other design elements incorporated into its construction. Adequate crawlspace drainage is not something that geotechnical consultants can verify; the purpose of our visit is for observations of foundation bearing conditions only. Appropriate design professionals should be consulted regarding crawlspace ventilation, building material selection and mold prevention issues, which are outside GeoPacific's area of expertise. We have prepared this report for Stonebridge Homes, 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. `,j l rt • / Q,f:_":r,I / d3 , J�,�.._ D. EXPIRES:I06/30/20 21 James D. Imbrie, G.E. Geotechnical Engineer