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August 22nd 2022 G-5756 <br /> Ben Erickson Page 4 <br /> Seismic Site Design Classification and Design Parameters <br /> Based on guidance provided in the 2018 edition of the International Building Code(IBC), it is <br /> our opinion that the project site meets the criteria for seismic Site Class C for very dense Soils <br /> and soft rock. Seismic design parameters applicable for the site,based on the assigned Site Class <br /> C and design calculations per the 2018 IBC, are as follows: <br /> Ss= 1.351 g Sms= 1.621 Sds= 1.081 <br /> Si =0.479g Sml =0.718 Sal =0.479 <br /> The peak ground acceleration for the site, adjusted for the assigned site class, is 0.583g based on <br /> USGS seismic hazard design mapping per the 2018 IBC <br /> Foundations <br /> Soils that are anticipated to be acceptable for building support were encountered at a depth of <br /> approximately 1 foot bgs in the hand auger borings that were completed for our investigation. <br /> Based on these findings, it is our opinion that new foundations for the project can consist of <br /> conventional concrete strip and column footings that bear directly on dense or very dense native <br /> soils or on compacted, crushed rock structural fill that has been placed on a subgrade of dense or <br /> very dense native soils. Our recommended design criteria for conventional footing foundations <br /> supported on native soils or crushed rock structural fill are provided below. <br /> -Allowable bearing pressure, including all dead and live loads: <br /> Undisturbed,dense or very dense soil =2,000 psf <br /> Structural fill placed on dense or very dense soil =2,000 psf <br /> -Minimum depth to base of perimeter footing below adjacent exterior grade= 18 inches <br /> -Minimum depth to bottom of interior footings below top of floor slab= 12 inches <br /> -Minimum width of wall footings= 16 inches <br /> -Minimum lateral dimension of column footings=24 inches <br /> -Estimated post-construction settlement=1/2 inch <br /> -Estimated post-construction differential settlement across building width=1/2 inch <br /> A one-third increase in the above allowable bearing pressures can be used when considering <br /> short-term transitory wind or seismic loads. Lateral loads against the building foundations can be <br /> GEO Group Northwest,Inc. <br />