Failure of an unfilled landfill cell due to an adjacent steep slope and a high groundwater level: A case study

Abstract

Stability is a factor of vital importance for landfills, during both construction and operation. Slope failures are likely to occur in landfills located in regions with soft soils and a high groundwater table. In this study, the failure of an unfilled landfill cell, located in a typical coastal soft soil area, was explored. The failure was found to be caused by the instability of a continuous slope formed by the unfilled landfill cell and an adjacent construction waste landfill. A series of post-failure field investigations were performed, including cone penetration tests, monitoring of horizontal displacement of the sliding body, and an investigation of the groundwater. Additionally, finite element modeling and limit equilibrium analysis were applied to study the failure mechanism and the factor of safety (FOS), respectively. Both the field investigations and the theoretical analyses indicated that the geometrical configuration and the soft substratum provided the basis for the formation of the sliding surface, while a rise of the groundwater level due to continuous rainfall and poor drainage condition triggered the failure. This case reveals that the stability of landfills in regions with soft soils should be thoroughly assessed, and that appropriate ground treatment is necessary to avoid potential sliding along soft substrata. Furthermore, special attention should be paid to determination of the safe distances to surrounding earth structures, considering the effect of any ground treatment applied.