Influence of Foundation Soil on the Seismic Factor of Safety of Geosynthetic-Lined Solid-Waste Landfills: Equivalent Linear Approach

Abstract

This paper is focused on the influence of foundation soil on the seismic factor of the safety of a typical side-hill type solid-waste landfill. New analytical expressions are derived and presented to calculate the displacement, shear strain, and seismic accelerations within the landfill body and in the foundation soil. A new equivalent-linear-based approach is proposed to compute the seismic factor of the safety (FSavg) of municipal solid waste (MSW) landfills considering the effect of the foundation type. In the present study, four different foundation types are considered: shallow sand deposit (foundation type I), deep sand deposit (foundation type II), shallow clay deposit (foundation type III), and deep clay deposit (foundation type IV). Moreover, the proposed method considered the strain-dependent equivalent-linear material parameters (secant shear modulus and damping ratio) rather than a small-strain shear modulus and a fixed damping ratio. The acceleration ratios (ratio of surface to bedrock accelerations) obtained from the proposed method are in good agreement with the DEEPSOIL version 6.1 equivalent-linear results. The maximum shear strain within the landfill body significantly decreases with an increase in the input excitation frequency from 0.2 to 3 Hz. In addition, the landfill enters higher vibration modes. At higher vibration modes, a portion of the seismic acceleration acts in one direction, and the remaining portion acts in the opposite direction. This phenomenon reduces the net amount of acceleration acting on the landfill body that, in turn, results in a higher safety factor. The seismic factor of the safety values computed from the present equivalent-linear analysis is compared with the results of the present linear and pseudodynamic analyses. The parametric study revealed that the critical and safe foundation type for the seismic stability of MSW landfills also changes with a change in the input motion frequency. For an input frequency of 3.0 Hz, foundation type I is identified as the most critical one with the lowest FSavg, and foundation type IV is the safest one with the highest FSavg. Similarly, for an input frequency of 1.75 Hz, foundation type II is identified as the most critical foundation with the lowest FSavg, and foundation type III is on the safest side with the highest FSavg.