Performance Based Design for Seismic Design of Geosynthetics-Lined Waste Containment Systems

A performance-based methodology for seismic analysis and design of the geosynthetic elements of waste containment systems, including landfills and heap leach pads, has been developed. The methodology offers a rational alternative to the current state of practice for seismic design of geosynthetic containment system elements in which a decoupled Newmark-type displacement analysis is used to calculate a permanent seismic displacement. This calculated displacement is generally considered to be an index of the performance of the containment system in an earthquake. In the Newmark-type design methodology, no explicit evaluation is made of the stresses and strains in the geosynthetic elements of the containment system. In order to explicitly assess the ability of the geosynthetic elements of a containment system to maintain their integrity in a design earthquake, a finite difference model of waste-liner system interaction has been developed using the computer code FLAC^TM. A beam element with zero moment of inertia and with interface elements on both sides is employed in the model to represent a geosynthetic element in the liner system. This enables explicit calculation of the axial forces and strains within the liner system element. The beam element model was calibrated using available experimental data from shaking table tests of rigid and compliant blocks sliding on geomembranes. The model was then used to analyze the behavior of the Chiquita Canyon landfill in the Northridge earthquake. Results of the analysis provide insight into the reasons for the tears in the liner system at Chiquita Canyon observed after the Northridge event. This model provides a basis for direct performance based seismic design of geosynthetic elements not only in waste containment systems but in a variety of other civil structures that employ geosynthetic elements wherein earthquake ground motions cause relative displacement between the geosynthetic element and the surrounding soil.