Evaluating Ground Settlement above a Mined Area

Many states allow construction of landfills over previously mined areas. However, mitigation of the underground mines by filling or removal is often required prior to landfill construction. A settlement analysis for the proposed vertical expansion of a residual waste landfill is presented in this paper. The primary purpose of the analysis was to evaluate the possibility of subsidence of an underground mined area underlying the landfill in response to the proposed 31 m high vertical expansion. The analysis was performed using the software FLAC (Fast Lagrangian Analysis of Continua) which is a two-dimensional explicit finite difference code. The results of the analysis show that the proposed vertical expansion would not cause mine subsidence but it would cause a small amount of elastic ground settlement. As a result, no negative impacts to the existing engineering components of the landfill liner system are anticipated after completion of the proposed vertical expansion. This settlement analysis provides an alternative to removal or filling of underground mines to obtain regulatory approval as demonstrated by this vertical expansion project.