Evaluation of the Seismic Performance of a Class I Landfill

Geosyntec Consultants, Inc. performed an evaluation of the seismic performance of a Class I landfill in southern California as part of the engineering evaluation and cost analysis (EE/CA) of the landfill. Material properties for the cover soils, waste mass, and native materials were estimated from field and laboratory investigations. Numerical deformation analyses were performed using FLAC 7.0 to estimate the seismic response of the landfill to ground motions from potential large earthquakes on four nearby faults. To the best of Geosyntec's knowledge, this is the first time that this type of analysis has been used to evaluate the seismic performance of a landfill. The calculated horizontal displacements from the numerical deformation analyses exceed Newmark displacements by approximately one order of magnitude, which is attributed to the cyclic accumulation of shear strains under sustained static shear stress that is modeled in the numerical deformation analyses but is not directly represented in the Newmark analyses. Geosyntec also used a performance-based engineering approach to develop seismic performance standards that are based on preventing harmful discharges and allowing repairs of damaged landfill components to be completed within a timely manner to minimize harmful environmental impacts. For example, Geosyntec estimated the damage to landfill gas wells due to seismically induced displacements and compared the resulting air emissions to regulatory and health-based standards to allow development of contingency plans to repair the damage within a specified time period.