3535 RIVERFRONT BLVD Geotech Report 2023-02-22

September 24, 2018 HWA Project No. 2015-061-21 potentially liquefiable soils along geologic profiles A-A' through D-D' are presented on Figures 5A through 5D, respectively. 4.2.3 Post-Liquefaction Residual Shear Strength Analyses We assigned residual shear strengths for the potentially liquefiable soils using Idriss and Boulanger(2007) relationships. The residual shear strengths assigned are a function of the equivalent clean sand SPT value, (N i)6ocs,potential for void redistribution, and the initial effective overburden stress. We assumed the void redistribution effects could be significant, resulting in the most conservative (lowest) estimate of residual shear strength. The liquefiable zones were assigned different values of residual shear strength parameters based on average (NI)6ocs and effective overburden stress values. 4.2.4 Liquefaction-Induced Settlement Loose sand deposits tend to densify when they are subject to earthquake shaking. For saturated sand deposits, excess pore water pressure builds up during the earthquake excitation, leading to loss of strength or liquefaction. After the shaking stops, excess pore water pressures dissipate toward a zone where water pressure is lower, usually the ground surface. The dissipation is accompanied by a reconsolidation of the loose sand (Ishihara and Yoshimine, 1992). The reconsolidation is manifested at the ground surface as vertical settlement, usually termed as liquefaction-induced settlement or seismic settlement. The potential for liquefaction-induced settlement was evaluated at the existing boring profiles within the 3-Acre Park project area. The methodologies used were developed by Yi and Andrus (2010), and are generally based on the relationship between shear wave velocity, cyclic stress ratio, corrected SPT blow counts, and volumetric strain. Using these methods, liquefaction- induced settlement along the project alignment was estimated to vary from 4 inches to 18 inches. We expect that the liquefaction-induced settlement will be differential in nature. Liquefaction induced settlement generally occurs after the earthquake shaking stops and the pore pressures dissipate. Therefore, any loads associated with liquefaction induced settlement should be decoupled from the inertial seismic evaluations. 4.2.5 Design Considerations Due to Liquefaction Susceptible Soils Our analyses indicate that the site is underlain by granular materials that are to varying degrees susceptible to liquefaction for the design event being considered. Liquefaction of the subsurface soils will impose additional loads to be applied to the crane foundations, as well as contribute to slope instability for most the river bank slopes on the site. Loads on the proposed foundations of the crane structure will include significant vertical downdrag loading as well as lateral loading caused by slope instability/lateral spreading. Liquefaction induced settlement is expected to affect the restroom structure and associated utilities. The restroom structure should be designed to accommodate liquefaction induced settlement while maintain life safety. Final Geotechnical Report-3-Acre Park.docx 9 HWA GeoSciences Inc.