Characteristics of overburden failure and evolution of fractures in fully mechanized top coal mining face

The characteristics of overlying strata failure and the evolution law of fractures during coal mining are of great significance for mine water prevention and gas control. To further study the overlying strata failure characteristics and fracture evolution in fully mechanized top-coal caving (FMTC) mining faces, a Shanxi coal mine was selected as the experimental site. Methods such as segmented water injection, borehole television imaging, and microseismic monitoring were employed to detect the failure height of the overlying strata. A digital analysis was conducted on the relationship between fracture dip angle, quantity, and width before and after mining, along with numerical simulations of fracture evolution during the mining process.The results show that the overlying strata failure height in the FMTC mining face ranges from 127.3 m to 132.2 m. Before mining, fracture development was relatively low, whereas after mining, the number of fractures significantly increased, indicating enhanced fracture development. Pre-mining fractures were primarily characterized by high angles and low widths. As the coal face advanced, the number of fractures rose linearly, with the newly formed fractures mainly exhibiting small angles and medium widths. During mining, fractures predominantly concentrated around the coal wall, and the density distribution curve of overlying strata fractures showed a "wave-like" pattern, with higher values at both ends and the middle.