Evolution of mining-induced water inrush disaster from a hidden fault in coal seam floor based on a coupled stress-seepage-damage model

Water inrush originating from hidden faults in the coal seam floor is challenging to prevent due to their concealed nature. This paper develops a coupled stress-seepage-damage model for simulating rock fracture, implemented using the finite element method. The model is validated against compression-seepage tests on rock samples, capturing realistic dynamics of shear and tensile damage as well as permeability. The model is applied to the 27305 working face of a coal mine in Shandong Province, China, revealing the evolution of water inrush caused by a hidden fault. The results indicate that as the working face progresses, both the floor damage and the internal damage within the hidden fault escalate gradually. When mining reaches 80 m, the hidden fault has been activated internally, and the depth of floor damage reaches 13 m, which still has a certain distance from the hidden fault. At 100 m, the depth of the floor damage has stabilized, while the stress concentration at the hidden fault's tip increases, and it begins to expand if conditions for tensile damage are met. By the time mining reaches 110 m, the hidden fault has expanded 9.2 m in length and connected with the floor damage zone, forming a water inrush channel that links the aquifer to the working face, presenting a significant water inrush risk. This work provides an intuitive approach to understanding the evolution of water inrush from a hidden fault, aiding in the prevention of water inrush disasters in practical engineering applications. A coupled stress-seepage-damage model was proposed to simulate the dynamics of hidden faults during the mining process. The model has been validated with several small-scale laboratory compression-seepage tests to demonstrate its capabilities. By applying the proposed coupling model to a real-world coal mining operation, we demonstrate the process of hidden faults fracture propagation in the floor strata during the working face excavation, which might lead to a water inrush disaster. The most critical scenario occurs when concealed faults are positioned beneath the working face, resulting in a significant increase in the compressive stress borne by these hidden faults. This increase continues until a damaged state is reached, thereby triggering the propagation of fractures. Microseismic monitoring technology proves to be an effective measure to prevent water inrush caused by hidden faults, and in our application, microseismic event distributions near the working face are consistent with our numerical analysis results.