1710 W MARINE VIEW DR Geotech Report 2023-12-29

Liquefaction -induced free -field ground settlement of the potentially liquefiable zones was estimated using the semi -empirical approaches proposed by Tokimatsu and Seed (1987), Ishihara and Yoshimine (1992), and Idriss and Boulanger (2008) at the MCE level on B-1, B-2, and B-4 since these three borings went down to the glacially consolidate soils while the other three borings (B-101 through B-103) stopped at a shallower depth. Our analyses indicate that the site (under existing conditions) could experience liquefaction -induced free -field ground settlement on the order of 16 to 24 inches during an MCE seismic event, as shown in the Liquefaction -Induced Free -Field Ground Settlement, Figure 5. The differential liquefaction -induced settlements are anticipated to be on the order of 0.3 to 3.2 inches over a horizontal distance of 50 feet. 4.3. Lateral Spreading and Kinematic Loads Lateral spreading involves lateral displacements of large volumes of liquefied soil. Lateral spreading can occur on near -level ground as blocks of surface soils are displaced relative to adjacent blocks. Lateral spreading can also occur as blocks of surface soils are displaced towards a nearby slope or free -face by movement of underlying liquefied soil. In the case of this project site, lateral spreading could occur during earthquakes resulting in the excessive movement of the buildings. 4.3.1. Earthquake -Induced Lateral Ground Deformations Earthquake -induced lateral ground deformations were evaluated by performing slope stability analyses and simplified Newmark analyses for the Cascadia Subduction Zone (CSZ) intraslab source since the intraslab source has the highest percent contribution per deaggregation. 4.3.LL Slope Stability Analysis Slope stability analyses were completed on Cross Section A -A' using Limit Equilibrium Method (LEM) with a commercial software, Slope/W, developed by GEO-SLOPE International, Ltd. The slope stability was evaluated under static, seismic, and post -earthquake conditions. 4.3.1.2. Soil Properties The soil properties that were used in the slope stability analyses are listed in Table 3, where static strengths were used in static condition for all soil units. We assumed that liquefaction occurs during the earthquake; therefore, in seismic and post -earthquake conditions, residual friction angles were used in the liquefied soils (below groundwater table and above liquefaction depth); 80 percent of static strengths were used in the soils above groundwater table; and full static strengths were used in the soils (non -liquefiable) below liquefaction depth. GEOENGINEERS April 1.2022 Page 5 File No. 06 6-030 00