Determination of Longwall Mining-Induced Stress Using the Strain Energy Method

Extraction of the coal seam causes stress redistribution around the mined panel in longwall mining. The weight of bridging strata and strata that cantilevers over the destressed zone is shifted to adjacent gates, pillars, and abutments surrounding the longwall panel. Thus, knowledge of the mining-induced stress is very important to enable accurate design of gate supports and pillar dimensions. In this paper, an analytical model based on the strain energy balance in longwall coal mining is developed to determine the mining-induced stress over gates and pillars. In the proposed model, the height of the destressed zone above the mined panel, total induced stress, abutment angle, vertical component of induced stress, and coefficient of stress concentration over gates and pillars are determined analytically. As a case study, the proposed model is used to determine the coefficient of stress concentration over the gates and pillars in Tabas coal mine of Iran. In order to evaluate the effect of the proposed model's incorporated parameters on the coefficient of stress concentration, a sensitivity analysis is conducted based on the actual data of Tabas coal mine. Also, the proposed model is validated against the in-situ measurement as well as numerical and analytical models with the same boundary conditions. The validation results show that the proposed model is in agreement with the in-situ measurement and numerical model, but has differences compared with the available analytical models. Considering the obtained results, it can be concluded that the proposed analytical model can be used to calculate the mining-induced stress, aiming to reach the optimum design of gate supports and pillar dimensions.