Mechanism of Floor Failure During Coordinated and Sustainable Extraction of Coal and Geothermal Resources in Deep Mines: A Case Study

Achieving the sustainable development and utilization of mining energy resources necessitates the promotion of coordinated extraction of coal and geothermal resources. However, the direct discharge of untreated mine water not only leads to the dual wastage of water and geothermal resources but also poses environmental risks such as heavy metal contamination. Consequently, establishing an integrated green mining model that combines the recovery of coal, water, and geothermal energy has become an imperative for the sustainable development of the industry. Within this context, ensuring the stability of the floor strata during simultaneous coal mining and geothermal extraction represents a critical scientific challenge determining the safe and efficient implementation of this integrated technology. This study first presents the overall framework of a Simultaneous Extraction of Coal and Geothermal Resources (SECGR) technical system. Subsequently, through theoretical modeling and numerical simulation, we systematically studied the dynamic stress redistribution patterns and failure mechanisms within the bottom strata during the mining disturbance and extraction unloading process (MD-EU). The findings reveal that the vertical stress field exhibits an asymmetric distribution under the combined mining operations, while the shear stress field forms a distinctive saddle-shaped arch structure. The failure process of the floor strata undergoes four typical stages: the pristine state, crack initiation, crack propagation, and crack coalescence. Based on this, three characteristic zones are identified: the mining-induced failure zone, the water-resistant zone, and the unloading-activated zone. Finally, the Burgers viscoelastic model is employed to successfully quantify the time-dependent evolution of rock mass damage following mining-induced stress release. The research outcomes provide crucial theoretical support and technical guidance for safely advancing multi-energy coordinated extraction and enhancing the comprehensive resource utilization efficiency of mining systems.