A Strain-Dependent Modified Pseudodynamic Analysis of Expanded Landfill Stability under Leachate Conditions

This study examines the seismic stability of side-hill type expanded landfills using a modified pseudo-dynamic approach, explicitly considering leachate accumulation. The dynamic parameters of the material are modeled as strain-dependent using the equivalent linear approach, rather than being assumed as constant low-strain values. Waste heterogeneity is addressed by accounting for variations in unit weight, shear wave velocity, and permeability through the pore pressure ratio. Two failures: under berm and over berm with composite failure surface within the waste are considered for the translational failure analysis. Horizontal and vertical seismic force profiles are evaluated in the time domain to identify the instant when the combined effect produces the minimum factor of safety (FS). It is observed that for wave frequencies lower than the fundamental frequency, bedrock vertical seismic acceleration (av0 >0) is found to be more critical, whereas for frequencies higher than the fundamental frequency, av0 <0 is more critical. The seismic acceleration profile is also found to depend on the foundation type. The pseudostatic results for frequencies near the fundamental frequency underestimate FS, while frequencies further away overestimate FS. A reduction in FS of about 6% is observed for both failure conditions when strain effects are included. When leachate buildup is considered horizontal to the subgrade and parallel to the backslope, the FS decreases by about 7%, making this the most critical condition.