31C - CUP - 803 S SULLIVAN ST - Laserfiche WebLink

Home Browse Search

City of Santa Ana Environmental Checklist • Establishing earthwork procedures to address soils and subsurface conditions, including liquefaction. • Recommending foundations, soils preparations, and slabs be designed to resist the effects of lateral pressures. a3. Seismic-related ground failure, including liquefaction? Less-than-Significant Impact with Mitigation Incorporated. Soil liquefaction is a phenomenon in which saturated, cohesionless soils layers, located within approximately 50 feet of the ground surface, lose strength due to cyclic pore water pressure generation from seismic shaking or other large cyclic loading. During the loss of stress, the soil acquires "mobility" sufficient to permit both horizontal and vertical movements. Soils that are most susceptible to liquefaction are clean, loose, saturated, and uniformly graded fine-grained sands that lie below the groundwater table within approximately 50 feet below ground surface. The Soil Report identified liquefaction as a potential geological condition of the project site (Appendix B). Also, according to both Exhibit 5 of the Seismic Safety Element of the City's General Plan and the California Department of Conservation Division of Mines and Geology (CDMG) Seismic Hazards Zone Map for the Newport Beach Quadrangle (California Department of Conservation, Division of Mines and Geology 1998), the project site is located within a liquefaction area where historic occurrence of liquefaction or local geological, geotechnical, and groundwater conditions indicate a potential for- permanent ground displacements. Historical high groundwater elevations below the project site are as shallow as four feet bgs. For preparation of the Soil Report, a 50-foot-deep boring was drilled at the project site to measure for depths to groundwater. Groundwater was encountered at nine feet bgs. The geologic map of the site shows that the project area is located within a broad flat alluvium/clluuvium area, and the Soil Report identifies silty fine sand and silty clay underlying the project site. The project site is mapped by the CDMG as an area of liquefaction hazard. The Soil Report includes a liquefaction analysis that indicates the calculated total and differential settlements due to liquefaction are about 1.55 and 1.0 inches, respectively. The Soil Report also states that to reduce the potential adverse effects due to potential differential settlement due to potential liquefaction, the project shall include a strengthened foundation system with grade beams, and states that a mat foundation and/or caissons can be used for support of the purposed structure. As described above, the proposed project would comply with all CBC requirements and standards related to liquefaction. Additionally, as required in Mitigation Measure GEO.1, the proposed project would comply with all geotechnical recommendations provided in the Soil Report (Appendix B) to minimize potential impacts related to liquefaction. Therefore, potential impacts related to seismic- related ground failure, including liquefaction, are less than significant with implementation of Mitigation Measure GEO-1. a4. Landslides? Less-than-Significant Impact. Landslides and other slope failures are secondary seismic effects that are common during or soon after earthquakes. Areas that are most susceptible to earthquake- induced landslides are steep slopes underlain by loose, weak soils, and areas on or adjacent to existing landslide deposits. As discussed in VLal, the proposed project site is located in a seismically active region subject to strong ground shaking. However, according to the CDMG Seismic Hazards The Bat Nha Buddhist Meditation Center 3-35 June 2013 Initial Study/Mitigated Negative Declaration ICF W215.12 31 C-88