Coal mining above a confined aquifer

Mining above a confined aquifer involves the risk of a water in-rush to the mining face through broken floor strata. Thus, safe mining should take into account the important factors which influence the fracture behavior in rock strata. From the geological point of view, these factors, on the one hand, include geological structures, mechanical properties and permeability of floor strata, the thickness of waterproof strata separating the coal seam from the confined aquifer, in situ stress state and hydraulic pressure of the confined aquifer. On the other hand, mining parameters factors include length and rate of the mining advance, the length of the mining face in the longwall mining system, and the face interval between the double mining panels if any. Focused on fracture behavior and extent in floor strata with reference to the double face mining above the confined aquifer in Yangzhuang colliery, People's Republic of China, this work includes a systematic and comprehensive study which covers the in situ survey of the geological structure and hydraulic process, laboratory experiments on the mechanical and permeating properties of rocks, and in situ measurement of stress and fluid flow in the floor strata and the pressure distribution in the mining gateways. To gain a better understanding and insight into fracture initiation and development in the floor strata during the mining process, both physical and numerical models were employed. The final fracture depth in the floor strata primarily depends on the geological and hydraulic conditions, while mining parameters are of secondary importance. From a comprehensive analysis of fracture behavior in the floor strata, the importance of an effective in situ survey for geological structures has been emphasized. The adoption of room and pillar or strip and pillar mining system is recommended to avoid a water in-rush catastrophe. (C) 2003 Elsevier Science Ltd. All rights reserved.