Research and engineering practice of high stage and long span complex goaf filling treatment technology.

The long-term mining of lead-zinc ore bodies in Suichang Gold Mine has formed a high-stage, long-span columnar goaf group above 500 m elevation, posing significant risks of roof collapse, slope fragmentation, and ground pressure disasters. These hazards threaten the safety of deep mining operations and surface stability. To address these challenges, this study integrates field investigations, laboratory rock mechanics experiments, and FLAC3D numerical simulations to analyze the stability evolution of goafs before and after filling. Key innovations include the application of disaster chain theory to interpret goaf failure mechanisms and the optimization of cement-sand ratios for targeted filling (1:20 for 260-610 m levels and 1:8 for 528-540 m levels). Results demonstrate that cemented filling reduces vertical displacement by 2-4 cm, alleviates stress concentration (maximum compressive stress decreased by 0.5-1.0 MPa), and minimizes plastic zone expansion. Furthermore, the proposed interval mining sequence (first mining 300-390 m, followed by 260-290 m and 420-500 m levels) ensures both production efficiency and operational safety. This research provides a systematic framework for goaf management in complex mining environments.