Mining Thickness Determination of Upper and Lower Protective Coal Seam in Pressure Relief Mining

The reasonable selection of the protective coal mining (PCS) thickness and the quantitative relationship between the mining thickness and the interlayer spacing directly affect the performance of the pressure relief gas drainage and the safe mining of the PCS. Thus, the evolution of the protected coal seam (PDCS) permeability under the different PCS mining thickness in Huainan and Hancheng mining area is simulated by using the stress-damage-seepage coupling model. The results show that the PDCS permeability presents an S type increasing with the increase of the mining thickness. The logistic function formula for quantitative analysis of the relationship between the PCS mining thickness and PDCS permeability is given. The optimal mining thickness of the PCS in Huainan and Hancheng mining area is 1.73m and 0.96m, respectively, and the reasonable mining thickness range is 0.87-4.06 and 0.68-1.32m. Based on the numerical simulation, the quantitative curve between the mining thickness and the interlayer spacing of the upper and lower PCS mining in Hancheng and Huainan mining area is presented. Finally, the reliability of the numerical simulation is verified by the filed measurement of the fracture development in the roof and the permeability of the PDCS.