Seismic Stability Analysis of Expanded MSW Landfill Considering Composite Failure Surface in Translational Mode

Abstract

Vertical expansion in existing landfills is accomplished using an engineering berm at the toe of the landfill, which is a better alternative to horizontal expansion and new landfill construction from economic and environmental points of view. In this study, the pseudostatic limit equilibrium seismic stability analysis of a side-hill type landfill that was expanded using an engineered berm, which considers a composite failure surface, was performed. The waste heterogeneity was incorporated by considering the unit weight variation with depth. Two failure conditions were considered for the expansion of municipal solid waste (MSW) landfills: (1) under berm failure (when the waste mass slides with the berm); and (2) over berm failure (when the waste mass slides over the back slope of the berm). Based on the geometrical parameters, different landfill geometric models were considered in this study. Closed-form solutions for the average factor of safety (FS) and yield acceleration coefficient were developed. The expanded landfill could safely resist a horizontal seismic acceleration of 0.18g under the most critical situation. When the back slope of the berm became steeper than 3.85H:1V, the failure condition shifted from over to under berm. The location of the potential failure surface depended on the shear strength parameters of the waste and liner material. In addition, the failure surface shifts from passing within the landfill to along the liner with a change in the internal friction angle of the waste material from 30˚ to 35˚, which facilitates material selection for liners. The maximum height to which the volume of landfill could be safely increased was 110 m. The increase in population and industrialization causes a spike in waste generation, which leads to the requirement for waste disposal. In metropolitan cities, the most preferable disposal technique is a sanitary landfill. Due to the limited space of landfills, new landfills must be constructed, or the disposal space of current landfills must be increased. This study focuses on the methodology for the sustainable expansion of landfills vertically instead of horizontally, because horizontal expansion requires more space, which might not be feasible. Previous studies have presented vertical expansion in a landfill site in Xi’an, China, and the extension of a municipal solid waste (MSW) landfill in Guangzhou, China, with berms. This study considers the effect of the landfill shear strength parameters when determining the failure surface along the liner or within the landfill, which is a nuanced and realistic approach. This study presented pseudostatic seismic analyses with the composite failure surface, which resembles a more practical situation.