2401 TAYLOR DR Geotech Report 2022-10-25

2401 Taylor Drive Geotechnical Engineering Study Everett, Washington moisture-sensitive soil in structural fills should be limited to favorable dry weather and dry subgrade conditions and should not be used beneath foundation elements. The on-site soils contained substantial amounts of silt and are considered highly moisture-sensitive when excavated and used as fill materials. Construction equipment traversing the site when the soils are wet can cause considerable disturbance. If fill is placed outside of foundation areas during wet weather or if proper compaction cannot be obtained, a select import material consisting of a clean, free-draining gravel and/or sand should be used. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction and at least 25 percent retained on the No. 4 sieve. Slab-on-Grade Floor Support Slab-on-grade floors may be constructed either directly on the undisturbed, native soil or upon structural fill placed over these sediments. Areas of the slab subgrade that are disturbed (loosened)during construction should be recompacted to an unyielding condition prior to placing the capillary break, as described below. In order to control moisture vapor transfer through the slab, slab-on-grade floors should be constructed atop a capillary break consisting of a minimum thickness of 4 inches of washed pea gravel,washed crushed rock or other suitable material approved by the geotechnical engineer or engineering geologist. The capillary break should be overlain by a 10-mil (minimum thickness) plastic vapor retarder. Foundation Walls All backfill behind foundation walls or around foundation units should be placed as per our recommendations for structural fill and as described in this section of the report. Horizontally backfilled permanent walls, which are free to yield laterally at least 0.1 percent of their height, may be designed to resist active lateral earth pressure represented by an equivalent fluid equal to 35 pounds per cubic foot (pcf). Fully restrained, horizontally backfilled, rigid permanent walls that cannot yield should be designed for an equivalent fluid of 50 pcf. Permanent walls with sloping backfill up to a maximum gradient of 2H:1V should be designed using an equivalent fluid of 55 pcf for yielding conditions or 75 pcf for fully restrained conditions. If parking areas are adjacent to walls, a surcharge equivalent to 2 feet of soil should be added to the wall height in determining lateral design forces. As required by the 2015 IBC, permanent retaining wall design should include a seismic surcharge pressure in addition to the equivalent fluid pressures presented above. Considering the site soils and the recommended wall backfill materials,we recommend a seismic surcharge pressure of 8H and 10H psf, where H is the wall height in feet for the "active" and "at-rest" loading conditions, November 6, 2019 SONDERGARRD GEOSCIENCES, PLLC 9