3535 RIVERFRONT BLVD Geotech Report 2023-02-22

September 24, 2018 HWA Project No. 2015-061-21 constructed outside of flatwork areas wherever possible to allow for easy access if maintenance is required. Based on the fine-grained nature of the subsurface soils, onsite infiltration will not be feasible as a means of stormwater management for this project. Furthermore, discharging of stormwater over the existing riverbank, without bank stabilization, could increase slope instability and erosion. To limit effects on the riverbank we recommend that stormwater be routed to a dispersion faciality to the south of the project site. This dispersion facility should be located at least 100 feet from the bank of the river with a heavily vegetated flow path between the dispersion facility and the riverbank. For construction of a viewing platform for the crane (potential future phases of work), we recommend installing 16- to 18-inch diameter closed-ended steel pipe piles to rehabilitate the crane foundation or support a new concrete platform. To retain the fill proposed around the crane, we recommend installing sheet pile walls around the crane foundation. The sheet piles would need to be designed to resist that lateral earth pressure from seismic and post-liquefaction events due to the presence of liquefiable materials underlying the site. 4.2 SEISMIC CONSIDERATIONS 4.2.1 Seismic Design Parameters For the proposed 3-Acre Park improvements, we considered a design earthquake in accordance with the 2015 International Building Code (IBC). Seismic design parameters are developed based on a"Maximum Considered Earthquake" (MCE), which corresponds to an earthquake with a 2%probability of exceedance (PE) in 50 years (an approximate 2,475-year return period). The relevant probabilistic spectral response parameters were developed using the web tool provided for the 2012/15 IBC on the United States Geological Survey's website. The IBC accounts for the effects of site-specific subsurface ground conditions on the response of structures in term of site classes. Site classes are defined by the average density and stiffness of the soil profile underlying the site. The Site Class can be correlated to the average Standard Penetration Resistance (Nsp-r) in the upper 100 feet of the soil profile. Based on our characterization of the subsurface conditions, the 3-Acre Park site classifies as IBC Site Class D. Table 1 presents the design spectral seismic coefficients obtained for this site. Based on the SDS and SDI values, the site is considered as Seismic Design Category D. Final Geotechnical Report-3-Acre Park.docx 7 HWA GeoSciences Inc.