Mechanism of Water Inrush Induced by Gob Water Under Repeated Mining and Control Technology Based on Roof Cutting Pressure Relief

To mitigate the threat posed by accumulated gob water to underlying coal seams during multi-seam mining, this study investigates the mechanism of water inrush induced by repeated mining and its control through roof cutting pressure relief. The 31110 panel of the Holowan Coal Mine is taken as an engineering case, where the 3−1 coal seam is threatened by gob water from the overlying 2−2 coal seam. The mechanisms of interlayer rock mass damage accumulation, fracture interconnection, and water-conducting channel formation were systematically analyzed using a combination of theoretical analysis, numerical simulation, and field tests. The results indicate that the superimposed mining-induced failure zones of the upper and lower coal seams significantly exceed the interlayer spacing of 46.5 m. This condition promotes through-going damage of the interlayer strata and facilitates the downward migration of gob water. Without roof cutting, the main roof fractures toward the solid coal side of the 31110 auxiliary headgate, resulting in full connectivity of the overburden plastic zones and the formation of a continuous water-conducting channel. Roof cutting pressure relief, achieved by pre-inducing artificial weak planes, effectively guides roof fracturing toward the gob side, alleviates stress concentration on the solid coal side, and suppresses the expansion of interlayer damage. When the roof cutting height exceeds 35 m, plastic connectivity between the water-resisting coal pillar and the underlying mining-induced damage zone is interrupted, preserving the integrity of the key aquiclude. Field application of directional hydraulic fracturing roof cutting confirms the formation of continuous weakened fracture planes and controlled roof caving along the designed trajectory. The overburden caving angle increases from 70° to approximately 90°, effectively blocking water-conducting pathways and eliminating the risk of gob water inrush. These findings not only deepen the understanding of water inrush mechanisms under repeated mining disturbances but also establish a proactive fracture-regulation framework for gob water hazard control, providing broadly applicable design criteria and technical references for safe and efficient multi-seam mining in water-threatened coalfields.