Breaking process and mining stress evolution characteristics of a high-position hard and thick stratum

Based on the boundary support conditions of overlying high-position, hard and thick strata, a Winkler foundation beam mechanical model was built. Computational expressions for the characteristics and position of the bending moment for high-position, hard and thick strata were constructed by theoretical analysis, and the initial breaking position of high-position, hard and thick strata was also analyzed. The breaking process and evolution law of mining stress in high-position, hard and thick strata were studied by similar material simulation tests. Studies show that: due to the foundation deformation effect of the lower strata, the initial break position in high-position, hard thick layers is in the middle of goaf; vertical tension fractures first occur under the middle surface, then tilt tension fractures form at both sides and a non-uniform thickness of the fracture structure forms and produces subsidence deformation; behind the coal wall tilt fractures extend and eventually complete the migration. Mining stress produces obvious changes before and after the breakage of the high, hard and thick stratum; high stress concentration forms in front of the coal wall before breakage and fracture stress concentration significantly reduces after migration. Coal seam mining under high-position, hard thick strata can easily induce dynamic phenomena.