Study on fracture development and failure characteristics of repeated mining overlying strata in multi-coal seams with faults.

Taking a mine in Guizhou Province as the research background, a combination of similar simulation experiments and numerical simulation was used to analyse the spatial distribution of overburden collapse and the development of fissures during the mining process. The results indicate that: (1) During the mining of the upper coal seam, the overlying rock is not affected by faults, the 'three zones' are significantly developed, the collapse morphology exhibits a typical 'trapezoidal' structure, and the fractures undergo stages of formation, expansion, and closure; (2) The lower coal seam is affected by reverse faults, resulting in asymmetrical overburden collapse patterns and discontinuous fissure development. When mining across faults, periodic pressure is intense, and the stride length is significantly reduced, with severe rock fragmentation near the faults. (3) Under repeated mining activities, the displacement and subsidence of the lower coal seam are greater than those of the upper coal seam. By quantifying the spatio-temporal distribution of mining-induced fractures using fractal dimension, it is clear that their development and evolution follow a process of formation, development, and closure. The research results can provide a theoretical basis for the safe development of coal mines under similar geological conditions.