Influence of overburden combination structures on mining-induced fracture development and its height prediction for weakly consolidated formation in Western China

Underground space excavation, particularly in mining operations, significantly compromises the integrity of overlying rock-soil structures and ground infrastructure, resulting in issues. This study discusses how different overburden combination structures affect the development of mining-induced fractures and further predicts the height of the fractures in weakly consolidated formations in Western China. Using the matrix discrete element method, we analyzed the evolution and height development of water-conducting fractured zones (WCFZs) under three composite structures, including upper soft-lower hard (USLH), upper hard-lower soft (UHLS), and soft-hard interbedded (SHI) strata. Besides, field-measured data collected from weakly consolidated strata in Western China are applied to develop an empirical formula for predicting the failure height of the weakly cemented formations. The research results show that: (1) the mining-induced fractures develop more rapidly in hard rock than soft rock, and the steady fracture height varies significantly across different composite structures. (2) Based on the analysis of vertical stress, break heat distribution, and element connection, the mining-induced fracture height is highest in the UHLS strata (~ 130 m), followed by the SHI strata (~ 105 m) and then the USLH strata (~ 91 m), respectively. (3) The proposed formula, validated by measured data, demonstrates high prediction accuracy (94.89%), so the mathematical model can be well applied to predicting WCFZs in weakly cemented strata. This study provides new insights into the law of overburden failure and the height of mining-induced fractures during mining, especially the coal mines with the weakly cemented strata.