Fault Reactivation and Time-Dependent Water Inrush from the Seam Floor: A Mechanistic and Experimental Study

In deep mining, the coupled effect of high-pressure confined water and mining-induced stress reactivates minor faults, causing delayed floor water inrush and threatening safe, efficient coal extraction. This study systematically investigated the reactivation characteristics and delayed water-inrush mechanisms through theoretical analysis, large-scale non-hydrophobic physical model tests, and field practice. The results reveal that a higher degree of fault zone compaction and a smaller dip angle reduce the likelihood of reactivation. A modified non-hydrophobic physical modeling system was employed to capture the spatiotemporal evolution of floor displacement, stress, pore-water pressure, and water-conducting channels. The fracture evolution in the floor and fault zone follows a three-stage pattern: initial closure under front abutment pressure, continuous expansion after the working face passes the fault, and partial re-closure as the face moves away. Correspondingly, the delayed water-inrush process was characterized by three phases: initial floor failure, intermediate fault slip failure, and final erosional formation of water-conducting channels. Based on these findings, an integrated detection–assessment–prevention–verification technique was proposed and successfully applied in the field. This study provides a theoretical basis and technical guidance for preventing fault-induced water hazards under complex geological conditions.