Seismic Stability Analysis of Vertically Expanded Landfills under Different Leachate Buildup Conditions

Abstract

Expanding existing landfills offers a more economical and practical solution than constructing new disposal sites, especially in urban regions where land availability is limited. This study investigates the seismic stability of vertically expanded side-hill-type waste landfills while accounting for the combined effects of hydrostatic and hydrodynamic forces generated under six different leachate buildup conditions. Waste heterogeneity is incorporated by considering variations in unit weight with depth and changes in the pore water pressure ratio, ensuring a realistic representation of field waste behavior. Two translational failure modes, under-berm and over-berm failure, are evaluated using composite failure surfaces that develop through the waste mass. The closed-form solution indicates that the expanded landfill can safely withstand a horizontal seismic acceleration of 0.16 g. The leachate buildup that is horizontal to the landfill cell and parallel to the landfill back slope is identified as the most critical scenario. It is observed that when the internal friction angle of the waste decreases from 30° to 25°, the critical slip surface shifts from following the liner to passing through the waste, which has implications for liner material selection. A shift in the governing failure condition from over berm to under berm is observed when the berm back slope becomes steeper than the intersection point. The maximum safe expansion height of the landfill is determined to be 96 m for defined parameters.