Mining feasibility of middle coal seam in multiple coal seams influenced by the repeated mining based on the damage degree of interlayer strata

Based on a typical middle coal seam with the upper and lower goafs in close-multiple coal seams in Qianjiaying coal mine, the characteristics of the damage degree and the fracture development of the interlayer coal-rock mass were analyzed and the mining feasibility of the middle coal seam with the upper and lower goafs was determined, using a combination method with physical simulation, numerical simulation, and on-site measurement. The results showed that: ① Due to the repeated mining of the upper and lower coal seams, the average damage degree of the interlayer coal-rock mass increased, indicating lower damage degree and good integrity of the interlayer coal-rock mass. ② The longitudinal fractures in the interlayer coal-rock mass developed to the immediate floor of the middle coal seam. Longitudinal fractures emerged in each stratum of the interlayer coal-rock mass. No through-fractures were observed in the roof and floor of middle coal seam, or the seam itself. This maintained good continuity and integrity of the seam. ③ On-site industrial tests on the mining of middle coal seam showed that the maximum and average shield support capacity remained stable between 20.16~28.88 MPa and 14.83~17.32 MPa. These values never exceeded the rated shield support capacity of ZY4800-13/32 shield.