An investigation into the modeling of ground deformations induced by underground mining

Abstract

The mechanisms of strata deformation due to underground mining were analyzed in an effort to better understand immediate roof behavior and surface displacements. Strata deformation characteristics above longwall and room-and-pillar mines in the eastern U.S. coalfields were evaluated and a numerical procedure was developed for calculating surface displacements.

The model, based on the well-known finite element method, utilized empirical indices associated with subsidence engineering in order to incorporate the site-specific characteristics into the formulation. Different material behavior models and failure criteria were employed in an attempt to determine the areas highly deformed by underground excavation. Additionally, the method was sensitive to the ratios of the elastic moduli used to describe different rocks and/ or rock conditions, and not to the magnitude of the elastic properties. Thus, the use of arbitrary reduction factors to convert laboratory to in situ property values was completely avoided and scaling of the calculated surface displacements was based on, the empirically predicted, regional or local parameters. The use of fixed displacement nodes around an opening to induce failure overcame the roof-floor overlap problem encountered in other formulations.

The successful implementation of the proposed methodology for modeling surface deformations complements and enhances existing prediction techniques, which are primarily based on empirical approaches, by allowing parametric analysis for different excavation geometrics, roof convergence curves and overburden properties.