Study of pore pressure change during mining and its application on water inrush prevention: a numerical simulation case in Zhaogezhuang coalmine, China

Most of water inrush incidents in coalmines are originally derived from a seepage flow through rock mass fractures, particularly in fault zones. Water inrush is typically caused by hydromechanical coupling interactions induced by human activities. Taking the Zhaogezhuang coalmine in northern China as an example, the progress of a lagging water inrush, which occurred at a depth of about −1,100 m, was simulated and analyzed based on the hydromechanical coupling mechanism. A 3D model incorporating the main structures of the study area was constructed based on the geological data and field investigation. The equivalent continuum medium was employed to describe fault zones. Processes of determining the mechanical, rheological and hydraulic parameters are discussed in details. Three hydromechanical coupling models are applied: (1) the elastoplastic strain-fluid coupling mechanism in rock mass within the fault zone, (2) the inelastic creep-fluid coupling mechanism in rock materials within the fault gouge, and (3) the stress-permeability coupling mechanism in the fractured porous rocks. The evolution of water-recharge zones along the fault zone was presented in different mining phases. By comparing the simulated pore pressures with the in situ monitored ones, the following conclusions can be drawn: (1) the actual hydraulic behaviors are a combination of the long-term trends and short-term effects; (2) the creep-fluid coupling model reflects the rock hydraulic behaviors of long-term trends, while the elastoplastic strain-fluid coupling model demonstrates the short-term effects; (3) a prediction method called ‘time window’ for the risk of the lagging water inrush is proposed. Its feasibility is discussed.