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CITY OF SANTA ANA <br />Planning and Building Agency <br />Mr. Amir Houriani <br />Project No. 32-6235-00 <br />1601-1607N. Bristol Street <br />August 29, 2022 <br />Liquefaction <br />PageApproved <br />FOR PERMIT ISSUANCE <br />Master ID: <br />Date: <br />Liquefaction is the sudden decrease in the strength and stiffness of unconsolidated, saturated <br />cohesionless soils typically resulting from seismic ground shaking. For soils to liquefy, the <br />intensity and duration of the seismically induced cyclic loading must be enough to increase the <br />excess pore water pressures to such an extent that the effective stresses on the soil particles <br />reduces to zero. If liquefaction is initiated, the saturated soils behave temporarily as a viscous <br />fluid and consequently lose their capacity to support the structures founded on them. The <br />potential for liquefaction decreases with increasing clay and gravel content. Liquefaction potential <br />has been found to be the greatest where the groundwater level and loose cohesionless soils <br />occur within 50 feet of the ground surface. <br />According to the Seismic Hazards Zone Map for the Anaheim Quadrangle, the site is located in a <br />liquefiable area. This determination is based on groundwater depth records, soil type, and <br />distance to a fault capable of producing a substantial earthquake. Based on these conditions, <br />site -specific liquefaction analyses were performed to determine the presence of liquefiable <br />materials at the subject site and its potential effects. <br />Landslides <br />Seismically induced slope instability, mainly in the form of landslides, are common occurrences <br />during or soon after earthquakes. Review of the Seismic Hazard Zones Map of the Anaheim <br />Quadrangle indicates that the site is not located within a designated earthquake -induced <br />landslide zone. In the absence of significant ground slopes near the subject site, the potential for <br />seismically induced landslides to affect the proposed development site is low. <br />SEISMIC DESIGN CRITERIA <br />Liauefaction Potenti <br />To assess the potential for liquefaction, a site -specific liquefaction analysis was performed in <br />accordance with the provisions of Special Publication 117A Guidelines for Evaluating and <br />Mitigating Seismic Hazards in California (CGS, 2008). The analysis was conducted based on <br />empirical correlations with Standard Penetration Test (SPT) data obtained from Boring B-1 along <br />with laboratory testing of collected soil samples. The laboratory tests focused on determining the <br />fines content defined as the percentage passing the Number 200 sieve of the in -situ soils. <br />Results of these laboratory tests are presented on the enclosed Boring Log B-1, <br />Section 11.8.3 of ASCE 7-16 indicates that the potential for liquefaction shall be evaluated using <br />a site -modified peak ground acceleration (PGAm) corresponding to the Maximum Considered <br />Earthquake (MCEG). The OSHPD Seismic Design Maps Tool yielded a site modified peak ground <br />acceleration (PGAm) of 0.612g. The USGS Probabilistic Seismic Hazard Analysis Deaggregation <br />program (USGS, 2014) was used to determine the magnitude of the Maximum Considered <br />Earthquake (MCEc). The predominant earthquake magnitude correlated to a seismic event of <br />10% probability of exceedance in 50 years (475-year return period). <br />A.G.I. Geotechnical, Inc. • 16555 Sherman Way, Suite A • Van Nuys, CA 91406 <br />L Office: (818)785-5244 • Facsimile: (818)785-6251 <br />