Finite element modeling of stress distributions and problems for multi-slice longwall mining in Bangladesh, with special reference to the Barapukuria coal mine

Abstract

Abstract This paper deals with current coal mining operations under a mega-aquifer in NW Bangladesh, and presents a case study of underground mining in Barapukuria. The study uses numerical analyses to evaluate stress redistribution, strata failure, and water inflow enhancements that result from these coal extraction operations. A total of three models (A, B, and C) are presented in this study. Two-dimensional numerical modeling was performed to analyze the deformation and failure behavior of rock elements for two different models (A and B). For model A, we used an elastic finite element software package considering a Mohr–Coulomb failure criterion. For model B, we used boundary element method (BEM). The first two models were applied to determine the stress patterns. Model A provides the tectonic stress pattern of the basin, whereas model B represents the mining-induced stress field. The third model is a schematic model. The results of model A show that tensional failure of rock elements is concentrated in the Gondwana coal sequences as well as within the Eastern Boundary Fault (EBF) and its surroundings. Failure occurs in the middle to lower part of the model, and the magnitude of tensional stress in the shallow part is much greater than in the deeper part. Contours of τ max magnitudes are attributed to up-bending of the overburden, which would create numerous upward propagating fissures/fractures. The results of model B show that fracture propagation would be about 240 m upward for single-slice (height 3 m) mining extraction. From the contours of mean stress magnitudes, it is observed that the high range of fracture propagation increased upward for multi-slice extraction of coal. It is apparent from the fracture heights that large amounts of caving would occur towards the roof due to the multi-slice extraction of coal, and finally would be linked with the water-bearing Dupi Tila Formation. If this happened, it would ultimately cause a major water inflow hazard in the mine.