1020 N BROADWAY EVCC STUDENT HOUSING Geotech Report 2022-10-25

Proposal for Geotechnical Engineering Services Proposed Apartments: 1020 North Broadway, Everett, Washington September 27, 2017 4.0 GEOTECHNICAL RECOMMENDATIONS 4.1 SEISMIC DESIGN PARAMETERS The 2015 International Building Code (IBC) seismic design section provides a basis for seismic design of structures. Table 1 below provides seismic design parameters for the site that are in conformance with the 2015 IBC, which specifies a design earthquake having a 2%probability of occurrence in 50 years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps. Table 1 —Seismic Design Parameters Spectral Spectral Design Spectral Site Control Periods Acceleration Acceleration Response Site Coefficients [sec.] Class at 0.2 sec. [g] at 1.0 sec. [g] Parameters Ss Si Fa F,, SDS SDI To Ts C 1.264 0.481 1.000 1.319 0.843 0.423 0.100 0.502 The spectral response accelerations were obtained from the USGS Earthquake Hazards Program Interpolated Probabilistic Ground Motion website (2008 data) for the project latitude and longitude. Liquefaction Potential: Liquefaction is a process that can occur when soils lose shear strength for short periods of time during a seismic event. Ground shaking of sufficient strength and duration results in the loss of grain-to-grain contact and an increase in pore water pressure, causing the soil to behave as a fluid. Soils with a potential for liquefaction are typically cohesionless, predominately silt and sand sized, must be loose, and be below the groundwater table. The site is predominantly underlain by very dense silty sand with gravel without a defined groundwater table. Based on these conditions, in our opinion the liquefaction potential of the site is negligible and design considerations related to soil liquefaction are not necessary for this project. 17-233 1020 North Broadway Page 5 PanGEO,Inc.