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Geotechnical Engineering and Geological Hazard Study Lincoln Elementary School ;Modernization Project Manteca, California Page 8 located within 10 kilometers of a potentially active fault, not Site Class F, and the value of spectral acceleration at the one second wave length (SI) was less than 0.75, so a Site Specific Seismic Hazard Analysis was not required. 6.1.1 Design Parameters for Seismic Shaking We recommend the following values for structural design according to the 2013 CBC and USGS. These values are based on PGA= 0.354; PGA, =0.405; S, = 0.970; St = 0.348; Fa = 1.112; and F,. = 1.704. Adjusted Maximum Considered Earthquake Spectral Response Accelerations SIMS 1.079 SMI 0.593 Design Spectral Acceleration SDs 0.719 SDI 0.395 We recommend the using the following design values: SDS 0.72 SDI 0.40 6.2 LIQUEFACTION, SEISMIC SETTLEMENT POTENTIAL Liquefaction normally occurs when sites underlain by saturated, loose to medium dense, granular soils are subjected to relatively high ground shaking. During an earthquake, ground shaking may cause certain types of soil deposits to lose shear strength, resulting in ground settlement, oscillation, loss of bearing capacity, landsliding, and the buoyant rise of buried structures. The majority of liquefaction hazards are associated with sandy soils, silty soils of low plasticity, and some gravelly soils. Cohesive soils (clays) are generally not considered to be susceptible to liquefaction. In general, liquefaction hazards are most severe within the upper 50 feet of the surface, except where slope faces or deep foundations are present (CDMG Special Publication 117, 1997). The potential for an earthquake with the intensity and duration characteristics capable of promoting liquefaction is a possibility during the design life of the project. The liquefaction potential of the site soils was evaluated using the method described by Idriss and Boulanger (2008). A depth to groundwater of 10 feet was used based on the data from the local groundwater conditions (Section 5.2). A peak ground acceleration (PGA) of 0.405g and earthquake magnitude, Mw = 6.6 were used in the analysis of liquefaction potential and liquefaction -induced settlement. These values are based on the findings of the USGS design maps application site class D, USGS deaggregation, and CGS results. Settlement calculations were performed for soil strata with a factor of safety of less than 1.3.The results of the analysis indicated that a potential for liquefaction is present within some sand and silt layers, but most of these layers are confined within non -liquefiable layers of cohesive soils (clays), firm silts, dense sands, or a mixture of such liquefaction -resistant materials. Therefore the potential effects of liquefaction under these conditions are limited to minor settlement due to volumetric compression of the liquefied materials. Liquefaction settlement calculations were made using the methodology of Idriss and Boulanger (2008) and Liquefaction SPT Analysis software. The settlement analysis indicated that up to 1 to 2 inches of seismic settlement is possible from the surface to a depth of 50 feet, with most of the settlement in the upper 15 to 30 feet. Liquefaction is not expected to be widespread since potentially liquefiable silt layers identified are confined by strata high in fine content, relatively dense or stiff, or not susceptible to liquefaction. Furthermore, ground surface settlements should be significantly less due to bridging effects within the overlying compacted soil. Additionally, deeper and therefore older soils are less likely to liquefy because ow to ''E 4�. CONDOR