A time-independent energy model to determine the height of destressed zone above the mined panel in longwall coal mining

Longwall mining is the most widely used method in underground coal extraction. After the coal seam extraction, the strata above the mined panel will be destressed and then the overburden weights will be redistributed and transferred to the front abutment and neighboring solid sections. In this research, the height of destressed zone (HDZ) is taken as equivalent to the combined height of caving and fracturing zones above the mined panel roof induced due to longwall mining. Accurate determination of this height is essential to proper estimate of transferred loads toward the gates and pillars. In this paper, a time-independent analytical model based on the strain energy balance in longwall mining is developed to determine the HDZ. Unlike the previous analytical and empirical models, the proposed energy model incorporates both possible influencing geometrical and geomechanical parameters in calculating of HDZ. The model proposed sensitivity analysis shows that depth of cover, extracted coal seam thickness and unit weight have the direct influence and elastic modulus, Poisson ratio, uniaxial compressive strength and bulking factor have the inverse influence on the HDZ. The results of the proposed model are compared with the results of in-situ measurements and existing, analytical, empirical and numerical models reported in literature. The comparison results show that the proposed model complies with the comparable models as well as with the in-situ measurements. Therefore, it can be concluded that the proposed energy model can be successfully used to determine the height of destressed zone above the mined panel in longwall mining.

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