Degradation and Migration Characteristics and Water-Inrush Mechanism of Overburden Roof Under High-Intensity Mining

In the central and western regions of China, coal mining operations are progressively transitioning from shallow to deep strata. This shift is accompanied by an increase in mining height and a rise in the degree of automation, leading to uneven and potentially violent settlement of overlying rock formations, as well as the formation of single or multi-layer separation spaces above the coal seam. If the water-conducting fracture zone intersects with the water-bearing separation layer, it can result in catastrophic mine accidents such as water gushes and sand collapses on the working face. Based on the research background of a specific working face in the No.7 coal seam at Qianjiaying Mine, this study employs empirical formulas, BP neural networks, similarity simulations, and UDEC numerical simulations to investigate the evolution of overburden fractures and the development of separation layers under high-intensity mining conditions. The study also analyzes the water inrush modes and mechanisms of separation layers in high-intensity mining, leading to the following conclusions: (1) By collecting data from 42 different coal mining faces in China, empirical formulas and BP neural network prediction models for the development height of the water-conducting fracture zone in overlying rock were established. The relative and absolute errors of the prediction results from both models were compared. For 90% of the predicted data, the error rate of the BP neural network model was less than 0.5%, with an average error of approximately 3%. (2) Through two similar simulation tests, where only the mining height of the coal seam (3 and 6 m) was varied while controlling other variables, it was concluded that higher mining heights lead to more severe damage and obvious fracture development in overlying rock. The presence of a main key layer and thick sandstone increases the expansion time and duration of the separation space. Overburden failure in high-intensity mining exhibits a “Π” shape, with the failure height primarily influenced by the high-intensity mining mode, overburden structural combination, and the load of the “beam-arch structure,” as well as the overburden dilatation coefficient. (3) Numerical simulation results indicate that under different mining height conditions, larger mining heights result in more pronounced settlement of the main key layer, with step subsidence and sliding phenomena observed on both sides of the key layer. (4) Based on the aforementioned research methods, this paper explores the formation mechanisms of separation layers in both single-seam and multi-seam mining, focusing on the analysis of repeated disturbances in multi-seam mining, dynamic water inrush, and structural water inrush modes. It comprehensively elucidates the mechanisms of separation layer water inrush in high-intensity mining.