Evaluation of pore water pressure ̄uctuation around an advancing longwall face

Large deformations that accompany longwall mining result in complex spatial and temporal distributions of changes in undrained pore ̄uid 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 e€ect. A three-dimensional ®nite element model is applied to de®ne anticipated pore ̄uid response both around the advancing mining face, at depth, and in the near surface region. The results are carefully veri®ed against the response recorded at three well-instrumented longwall sites. Pore pressure changes are indexed directly to volumetric strains de®ning zones of signi®cant 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 con®rmed with available, short-term water level response data, de®ning the strongly heterogeneous spatial response and the signi®cance of well depth on anticipated water level response. Ó 1999 Elsevier Science Limited. All rights reserved