Numerical and experimental study of fracture evolution in layered sandstone and mudstone above the cavity

In accordance with the distinctive characteristics observed in the sandstone-mudstone composite roof within Zhaogu coal mine, Jiaozuo coalfield, this paper delves into the influence of the non-uniform key stratum of Dazhan sandstone, characterized by varying thicknesses, on the overall strength of the composite roof. A mechanical model for the sand-mudstone composite body, considering different sandstone thickness ratios, was established. The study employed ESLS DIC and AE systems to investigate the mechanical behavior. The findings reveal a general decline in compressive strength, with a stepwise reduction in post-peak stress correlating with diminishing sandstone thickness ratios in the combined samples. Specifically, when the sandstone thickness ratio is 25