9702 19TH AVE SE Geotech Report 2024-03-28

Pacific Ridge — DRH, LLC ES-7829.01 August 26, 2021 Page 14 The passive earth pressure and coefficient of friction values include a safety factor of 1.5. The vault walls should be backfilled with free-draining material or suitable common earth if a sheet drain material is used. The upper one foot of the wall backfill can consist of a less permeable soil, if desired. A perforated drain pipe should be placed along the base of the wall and connected to an approved discharge location. If the elevation of the vault bottom is such that gravity flow to an outlet is not possible, the portion of the vault below the drain should be designed to include hydrostatic pressure. Design values accounting for hydrostatic pressure are included above. ESNW should observe grading operations for the vault and the subgrade conditions prior to concrete forming and pouring to confirm conditions are as anticipated, and to provide supplemental recommendations as necessary. Additionally, ESNW should be contacted to review final vault designs to confirm the geotechnical design parameters recommended above have been incorporated into the plans. Vault backfill should be placed and compacted in accordance with the recommendations provided in the Structural Fill section of this report. Seismic Design The 2018 International Building Code (2018 IBC) recognizes the most recent edition of the Minimum Design Loads for Buildings and Other Structures manual (ASCE 7-16) for seismic design, specifically with respect to earthquake loads. Based on the soil conditions encountered at the boring locations, the parameters and values provided below are recommended for seismic design per the 2018 IBC. Parameter Value Site Class C* Mapped short period spectral response acceleration, Ss (g) 1.354 Mapped 1-second period spectral response acceleration, S1 (g) 0.479 Short period site coefficient, Fa 1.200 Long period site coefficient, Fv 1.500 Adjusted short period spectral response acceleration, SMs (g) 1 .624 Adjusted 1-second period spectral response acceleration, SM1 (g) 0.719 Design short period spectral response acceleration, SDs (g) 1.083 Design 1-second period spectral response acceleration, SD1 (g) 0.479 Assumes very dense soil conditions, encountered to a maximum depth of 30.5 feet bgs during the April 2021 field exploration, remain very dense to at least 100 feet bgs. Based on our experience with the project geologic setting (glacial till) across the Puget Sound region, soil conditions are likely consistent with this assumption. Earth Solutions NW, LLC