| A recent area of concern in geotechnical engineering is the seismic response of solid-waste landfills. The seismic response of waste repositories is of concern because dynamic loads may produce relative movements within the waste, bottom liner system, cover system, foundation and their interfaces. These movements could damage the liner, with a consequent loss of sealing, and/or disrupt the cover, or leachate and gas collection systems.; A series of one-dimensional, equivalent-linear wave propagation analyses are performed to examine the factors that influence the seismic response of solid-waste landfills. The results of these analyses, coupled with the corresponding analyses to calculate the expected permanent displacements, are used to assess the effects of seismic loadings on landfills. The maximum equivalent acceleration at the landfill-liner interface, which represents the shear stresses at the base of the sliding mass, depends significantly on the dynamic characteristics of the waste fill. The magnitudes of seismically induced permanent deformations along base liner and cover system interfaces depend on the waste fill's fundamental period, site conditions, and the intensity, frequency content and duration of the input acceleration-time history.; Recent earthquake events have provided opportunities to document and to examine the performance of solid-waste landfills. In particular, the 1994 Northridge earthquake provided the first data on the seismic performance of geosynthetically lined landfills. The performance of 22 facilities, including eight lined landfills, is examined. Overall, the performance of landfills during earthquake events has been satisfactory. None of the landfills showed any signs of major damage. However, one geosynthetically lined landfill experienced significant damage during the Northridge earthquake, with a series of tears observed in two geomembrane liner systems.; Much attention has been given recently to quantifying the dynamic properties of waste fill, including its unit weight, shear strength, shear wave velocity, and shear modulus degradation and damping characteristics as a function of shear strain. Whereas in situ testing techniques can offer reliable means for measuring unit weight and shear wave velocity, the difficulties of sampling and testing make the evaluation of the shear modulus degradation and damping characteristics of solid-waste from conventional laboratory testing techniques difficult at the present time. For this reason, back-analysis of landfill performance during earthquakes is an useful alternative. The Operating Industries, Inc. landfill, which is equipped with a pair of strong motion recording stations, provides such an opportunity. Back-analyses of this landfill utilizing the recorded motions from five earthquakes in two orthogonal directions are performed to examine the effects of variations of dynamic properties on the seismic response of the landfill. The results of a comprehensive statistical analysis of the calculated and recorded responses are used to develop a "best-estimate" range for the strain-dependent shear modulus degradation and damping characteristics of the solid-waste at the OII landfill. Finally, the seismic performance of four other landfills during the Northridge earthquake is back-analyzed to develop empirically calibrated estimates of the dynamic strength of waste fill, which is also difficult to evaluate in the laboratory. The observed performance of these landfills provides a valuable opportunity to investigate the accuracy and reliability of available procedures for analyzing the dynamic response of solid-waste landfills. |
