10930 HOLLY DR Geotech Report 2025-08-08

Helix Design Group,Inc.-Greenwood Heating&Air Conditioning,Everett,WA April 22,2022 Geotechnical Engineering Report Z0219 Slope Protection: We recommend that a permanent berm,swale,or curb be constructed along the top edge of all permanent slopes to intercept surface flow. Also,a hardy vegetative groundcover should be established as soon as feasible to further protect the slopes from runoff water erosion. Alternatively,permanent slopes could be armored with quarry spalls or a geosynthetic erosion mat. 4.2 Spread Footings In our opinion, conventional spread footings will provide adequate support for the proposed structures if the subgrade is adequately prepared. Footing Depths and Widths: For frost and erosion protection, the base of all exterior footings should bear at least 18 inches below adjacent outside grades,whereas the base of interior footings need bear only 12 inches below the surrounding slab surface level. To reduce post-construction settlements, continuous (wall) and isolated (column) footings should be at least 16 and 24 inches wide,respectively. Bearing Subgrades: Foundation elements should be constructed on medium dense or denser undisturbed native soils,or on structural fill bearing pads that extend down to medium dense or denser native soils. We anticipate that adequate bearing soils will be encountered at relatively shallow depths (less than 2 feet) across much of the proposed building area. Slight over- excavations may need to be performed towards the north end of the proposed building alignment in order to extend foundation elements below existing fill soils, to native glacial till deposits. In general,before footing concrete is placed,any localized zones of loose soils exposed across the footing subgrades should be compacted to a firm,unyielding condition,and any localized zones of soft,organic,or debris-laden soils should be overexcavated and replaced with suitable structural fill. Lateral Overexcavations: Because foundation stresses are transferred outward as well as downward into the bearing soils, all structural fill placed under footings, should extend horizontally outward from the edge of each footing. This horizontal distance should be equal to the depth of placed fill. Therefore, placed fill that extends 5 feet below the footing base should also extend 5 feet outward from the footing edges. Subgrade Observation: All footing subgrades should consist of firm,unyielding,native soils, or structural fill materials that have been compacted to a density of at least 95 percent (based on ASTM:D-1557). Footings should never be cast atop loose, soft, or frozen soil, slough, debris, existing uncontrolled fill, or surfaces covered by standing water. Bearing Pressures: In our opinion, for static loading, footings that bear on properly prepared, structural fill bearing pads,or densely consolidated,native, glacial till soils, can be designed for a preliminary allowable soil bearing pressure of 3,000 psf. A one-third increase in allowable soil bearing capacity may be used for short-term loads created by seismic or wind related activities. Migizi Group,Inc. Page 10 of 16 mn�iz�