Abstract: Mine confined water is a serious threat for the safety production of underground coal face. Through theoretical analysis, a mechanics model of crack tip was established, the equilibrium equation of fracture mechanics was deduced, and the crack propagation condition of floor water inrush caused by mining on high confined water were analyzed. In addition, evolution process of rock stress field, damage field and seepage field under mining were simulated by RFPA, and the mechanism of confined water inrush was further revealed. The results show that the propagation condition of water flowing crack is that the resultant force of pore water pressure and t in-situ stress should be greater than the internal cohesion of coal-rock mass. Surrounding rock stress distribution has been changed by mining activities, which also causes local stress concentration and damage within coal-rock mass. After a large-scale water inrush appears, the principal stress is significantly larger than that in crack initiation. Duo to internal damage, the permeability of coal-rock mass increases, and the affected area of seepage field also increases.

Key words: confined water, coal mining, floor water inrush, three fields, evolution