Laserfiche WebLink
Pacific Ridge — DRH, LLC ES-8528.01 <br /> July 18, 2022 Page 10 <br /> Seismic Design <br /> The 2018 International Building Code (2018 IBC) recognizes the most recent edition of the <br /> Minimum Design Loads for Buildings and Other Structures manual (ASCE 7-16) for seismic <br /> design, specifically with respect to earthquake loads. Based on the soil conditions encountered <br /> at the exploration locations, the parameters and values provided below are recommended for <br /> seismic design per the 2018 IBC. <br /> Parameter Value <br /> Site Class C* <br /> Mapped short period spectral response acceleration, Ss (g) 1.363 <br /> Mapped 1-second period spectral response acceleration, SI (g) 0.483 <br /> Short period site coefficient, Fa 1.2 <br /> Long period site coefficient, Fv 1.5 <br /> Adjusted short period spectral response acceleration, Sens (g) 1.636 <br /> Adjusted 1-second period spectral response acceleration, SMI (g) 0.725 <br /> Design short period spectral response acceleration, SDS (g) 1.091 <br /> Design 1-second period spectral response acceleration, SDI (g) 0.483 <br /> Assumes very dense soil conditions, encountered to a maximum depth of 10 feet bgs during the April 2022 field <br /> exploration, remain very dense to at least 100 feet bgs. Based on our experience with the project geologic setting <br /> (glacial till) across the Puget Sound region, soil conditions are likely consistent with this assumption. <br /> Liquefaction <br /> Liquefaction is a phenomenon where saturated and loose cohesionless soil suddenly loses <br /> internal strength and behaves as a fluid. This behavior is in response to increased pore water <br /> pressures resulting from an earthquake or another intense ground shaking. The referenced <br /> liquefaction susceptibility map indicates the project site maintains a very low susceptibility to <br /> liquefaction. In our opinion, site susceptibility to liquefaction may be considered negligible. The <br /> relatively dense and weakly cemented characteristics of the native soil and lack of a uniformly <br /> established, shallow groundwater table were the primary bases for this opinion. <br /> Slab-on-Grade Floors <br /> Slab-on-grade floors should be supported on a firm and unyielding subgrade consisting of <br /> competent native soil or at least 12 inches of new structural fill. Unstable or yielding areas of the <br /> subgrade should be recompacted or overexcavated and replaced with suitable structural fill prior <br /> to slab construction. <br /> Earth Solutions NW, LLC <br />