Evaluation of pore water pressure fluctuation around an advancing longwall face

Abstract

Large deformations that accompany longwall mining result in complex spatial and temporal distributions of changes in undrained pore fluid pressures around the advancing face. These seemingly anomalous changes are recorded in the rapid water level response of undermined and adjacent wells, and may be explained in the short-term as a undrained poroelastic effect. A three-dimensional finite element model is applied to define anticipated pore fluid response both around the advancing mining face, at depth, and in the near surface region. The results are carefully verified against the response recorded at three well-instrumented longwall sites. Pore pressure changes are indexed directly to volumetric strains defining zones of significant depressurization in the caving zone and in zones of extension adjacent to the subsidence trough on the ground surface. Overpressurization occurs in the abutment region, at panel depth, and in the surface compressive zone immediately inside the angle-of-draw. These results are confirmed with available, short-term water level response data, defining the strongly heterogeneous spatial response and the significance of well depth on anticipated water level response.