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BLACK AVENUE RESIDENTIAL DEVELOPMENT 648-26-1 Page 6 4.3.4 Ground Deformation and Surficial Cracking Potential The methods used to estimate liquefaction settlements assume that there is a sufficient cap of non-liquefiable material to prevent ground deformation or sand boils. For ground deformation to occur, the pore water pressure within the liquefiable soil layer will need to be great enough to break through the overlying non-liquefiable layer, which could cause significant ground deformation and settlement. The work of Youd and Garris (1995) indicates that the 30-foot thick layer of non-liquefiable cap is sufficient to prevent ground deformation and significant surficial cracking; therefore, the above total settlement estimates are reasonable. 4.4 LATERAL SPREADING Lateral spreading is horizontal/lateral ground movement of relatively flat-lying soil deposits towards a free face such as an excavation, channel, or open body of water; typically, lateral spreading is associated with liquefaction of one or more subsurface layers near the bottom of the exposed slope. As failure tends to propagate as block failures, it is difficult to analyze and estimate where the first tension crack will form. The current Arroyo Valle runs approximately 1,750 feet southwest of the site. The channel bottom is at approximately Elevation 324 feet. Therefore, the channel bottom is approximately 15 to 20 feet deep relative to existing site grades within the lower portion of the site. As part of our liquefaction analyses, we calculated the Lateral Displacement Index (LDI) for potentially liquefiable layers based on methods presented in the 2008 monograph,Soil Liquefaction During Earthquakes (Idriss and Boulanger, 2008). LDI is a summation of the maximum shear strains versus depth, which is a measurement of the potential maximum displacement at that exploration location. Summations of the LDI values to a depth equal to twice the open face height were included. Estimated displacements in the vicinity of CPT-1 through CPT-5 based on the LDI calculations are considered negligible. 4.5 SEISMIC SETTLEMENT/UNSATURATED SAND SHAKING Loose unsaturated sandy soils can settle during strong seismic shaking. As the soils encountered at the site were predominantly stiff to very stiff clays and medium dense to dense sands, in our opinion, the potential for significant differential seismic settlement affecting the proposed improvements is low. 4.6 FLOODING Based on our internet search of the Federal Emergency Management Agency (FEMA) flood map public database, the site is located within Zone X, defined as “Areas determined to be outside the 0.2% annual chance floodplain.” We recommend the project civil engineer be retained to confirm this information and verify the base flood elevation, if appropriate. The Department of Water Resources (DWR), Division of Safety of Dams (DSOD) compiled a database of Dam Failure Inundation Hazard Maps (DSOD, 2015). The generalized hazard maps Lateral spreading is horizontal/lateral ground movement of relatively flatLateral spreading is horizontal/lateral ground movement of relatively flat towards a free face such as an excavation, channel, or open body of water; typically, lateral towards a free face such as an excavation, channel, or open body of water; typically, lateral subsurface layers near the bottom of subsurface layers near the bottom of the exposed slope. As failure tends to propagate as block failures, it is difficult to analyze and the exposed slope. As failure tends to propagate as block failures, it is difficult to analyze and 1,750 feet southwest offeet southwest of feet. Therefore, the channel bottom is approximately feet. Therefore, the channel bottom is approximately feet deep relative to existing site grades within the lower portion of the site. As part of feet deep relative to existing site grades within the lower portion of the site. As part of our liquefaction analyses, we calculated the Lateral Displacement Index (LDI) for potentially our liquefaction analyses, we calculated the Lateral Displacement Index (LDI) for potentially liquefiable layers based on methods presented in the 2008 monograph,liquefiable layers based on methods presented in the 2008 monograph, (Idriss and Boulanger, 2008). LDI is a summation of the maximum shear strains (Idriss and Boulanger, 2008). LDI is a summation of the maximum shear strains versus depth, which is a measurement of the potential maximum displacement at that versus depth, which is a measurement of the potential maximum displacement at that exploration location. Summations of the LDI values to aexploration location. Summations of the LDI values to a height were included. Estimated displacements in the vicinity of CPTheight were included. Estimated displacements in the vicinity of CPT on the LDI calculations are considered negligible. on the LDI calculations are considered negligible. SEISMIC SETTLEMENT/UNSATURATED SAND SHAKINGSEISMIC SETTLEMENT/UNSATURATED SAND SHAKING Loose unsaturated sandy soils can settle during strong seismic shaking. As the soils Loose unsaturated sandy soils can settle during strong seismic shaking. As the soils encountered at the site were predominantly stiff to very stiff clays and medium dense to dense encountered at the site were predominantly stiff to very stiff clays and medium dense to dense