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Report (11) "49 zozz-z ygs GEDPIICIFIC Real-World Geotechnical Solutions Investigation•Design•Construction Support May 16, 2023 Project No. 22-6162 Ichijo USA Co., LTD Attn: Erik Gomez 1509 SW Sunset Blvd. Suite 2-D Portland, Oregon 97239 Via email to: erik.gomezAichiiousa.com FOUNDATION SUBGRADE REVIEW LOT 32 RIVER TERRACE CROSSING AKA CROSSING AT BULL MOUNTAIN 15228 SW DEEPBROOK LANE TIGARD, OREGON This letter addresses the single-family home foundation subgrade on Lot 32 of the River Terrace Crossing development, also known as Crossing at Bull Mountain. We understand that the proposed building is a two-story home with a stepped foundation for a daylight basement or tall crawlspace. As part of this evaluation, GeoPacific visited the site on May 1, 9, 11, and 12, 2023. On May 1, 2023 we observed two large areas of soft, existing fill material. We recommended that those areas be excavated down to reach competent native soils or engineered fill material. On May 9 and 11, 2023, we observed as the contractor excavated down and placed imported granular fill as backfill. Based on our observations, the contractor reached competent engineered fill material in the excavations. On May 12, we observed that the backfill had been adequately placed and compacted. The excavation on lot 32 is stepped down in three benches, with a depth of up to 6 feet below surrounding grades. The tallest bench was about 4 feet tall. The exposed subgrade on lot 32 appeared to consist of gravelly silt fill material placed during mass grading of the subdivision. However, I observed some native soil in the southeast corner of the house footprint. The contractor placed imported granular fill in the southwest and west portions of the basement, along the east side of the house on the second bench, and at the northwest corner of the house. Since some of the soils are granular, some structural fill may be necessary in the crawlspace. We will evaluate the configurations of the benches and footings after the foundation have been poured. The foundation layout of Lot 32 is stepped down to the south. Footing-to-slope and footing-to-wall setbacks did not appear to be an issue for the structure. 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. 14835 SW 72nd Avenue Tel(503)598-8445 Portland,Oregon 97224 Fax(503)941-9281 GeoPacific Engineering, Inc. Job No.22-6162 Lot 32 River Terrace Crossing 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%2-inch of loose soils are present prior to pouring concrete. Also, crushed rock placed over the surface of the subgrade should be compacted so that no more than approximately '/2-inch of loose gravel is 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 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 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 lchijo USA, 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. t r f Benjamin G. Anderson, P.E. Associate Engineer