An open-pit coalmine surcharged by artesian water pressure

Abstract

The Jiri Open-Pit Coalmine, with its highly productive coal measure, is located in a protected region of the Czech Republic that is famous for its spas and artesian thermal springs. A pressurized aquifer underlies the mine. The mining advance is limited by the hazard of potential hydraulic fracturing and resultant flooding of the mine, as well as by serious changes to the hydrogeological conditions of the whole region. To prevent this hazard, the aquifer pressure has been reduced by drainage wells. Between 1976 and the present time, estimates were made of the feasibility of the mining advance at a minimum pressure head reduction, i.e. for the minimum environmental impact. An interactive procedure has been implemented using numerical models calibrated using field measurements, and a monitoring system has been updated based on the results of the numerical analyses. The paper describes the predicted and observed performance of the mine in safe and critical conditions, the estimated failure mechanisms and the hydraulic fracturing incidents that have occurred, as well as different approaches used to assess the hydraulic fracturing hazard in various mining conditions.