Study on floor instability law of cemented filling mining above a confined aquifer

To solve the problem of floor water inrush in the process of coal mining on a confined aquifer and study the law of floor instability, a cemented filling mining method is proposed in the paper. Using river sand and cement as filling materials, the cementitious material with a concentration of 75% and cement content of 15% has the best flow and mechanical properties. Based on the elastic half-space theory and the bearing characteristics of the backfill, the mechanical model of floor stability is established, the critical criterion of floor instability is proposed, and the relationship between the failure depth of floor and the location and pressure of confined aquifer is obtained. The numerical simulation test scheme is designed, and the FLAC3D fluid-structure coupling element is used to explore the instability characteristics of the floor in the mining process. The research results show that the failure depth of the floor will gradually decrease with the increase of the strength of filling materials, the increase of aquifer distance, and the decrease of water pressure. The research results provide a useful reference for the study of safe mining of coal resources on a confined aquifer.