COMPLIANCE INFO_FINAL WMU FU-23 DESIGN RPT & CONCURRENCE LTRS

Home Browse Search

WMU FINAL WMU FU-23 DESIGN REPORT 2-18-23 3-2 SEISMIC HAZARD ANALYSIS Because the Forward Landfill is located in a seismically active area, stability analyses for final grade conditions must consider seismically induced forces on the refuse fill and slope. The Title 27 regulations require that landfills that accept designated waste be designed to withstand the maximum credible earthquake (MCE). The Forward Landfill, which is located in the Central Valley of California, has a history of low seismic activity. It is not located in an area of rapid geologic change. The surface projection of the Tracy- Stockton Fault Zone passes through the City of Stockton, 6.5 miles northwest of the site. This fault zone is the closest known to the landfill site and does not show evidence of Holocene displacement. No special containment structures are therefore needed for the landfill to preclude failure due to such events. A seismic hazard analysis (GLA, 2008) was performed for the Forward Landfill based on known active and potentially active faults and earthquake zones in California. Significant active and potentially active faults and seismic source zones within 100 miles (160 km) of the project site are listed in the analysis. Using an attenuation relationship for alluvial sites, a peak horizontal ground acceleration (PHGA) of 0.13g was estimated for the MCE event of 6.7 on the Green Valley 7 fault at a distance of 20.4 miles (32.9 km). However, the family of curves using other attenuation relationships for reverse faulting indicates an upper bound horizontal ground acceleration of 0.15g. A PHGA of 0.15g was, therefore, used in the seismic analysis. Based on the available historic data, the site has experienced a maximum acceleration of about 0.07g during a magnitude 8.25 earthquake on the San Andreas Fault in 1906 which occurred at a distance of about 73 miles (117 km). This is less than one-half of the PHGA of 0.15g that will be used for the site seismic design acceleration. 3.2 Stability Analysis The stability analyses are based on several measured and assumed material properties. The material properties used in the analyses and the results of the analyses are presented below. Calculations are included in Appendix B. 3.2.1 Material Properties The composite lining system for the WMU FU-23 base will consist of a 2-foot-thick clay liner overlain by a double-sided textured HDPE geomembrane, cushion geotextile, and granular blanket LCRS. Material properties used in the stability analyses were based on actual test data from previous WMUs constructed at the site and a review of published values in the literature. Table 3-1 presents the assumed material properties used in the stability analysis. The interface shear strength for the base lining system of WMU FU-23 was estimated using laboratory testing performed for the construction of the WMUs D-95 through WMU FU-19 lining systems. These interface shear strength results were assumed to be representative of those in WMU FU-23 because WMU FU-23 will be constructed using onsite soils and geosynthetic materials very similar to those used in these previously constructed WMUs. The interface shear strength properties used for the side slope liners were estimated using laboratory testing performed for the construction of WMUs D-97 through WMU FU-19. These interface shear strength results were assumed to be representative of those in WMU FU-23 because the same combination of materials was used in these previously constructed WMUs.