Strata‐Movement Concepts and the Hydrogeological Impact of Underground Coal Mining

Abstract

ABSTRACTA review of mining‐engineering concepts and studies in mine hydrology suggests a conceptual model linking the strata deformation, hydraulic property changes, and ground‐water impacts due to underground coal mining. The pressure‐arch deformation pattern about a small opening creates a local zone of increased permeabilities and dewatering in the seam and immediate roof, but should not hydraulically affect shallower aquifers. Networks of supported headings, rooms, and pillars intensely drain lower aquifers but only slightly affect higher strata except in areas of naturally high permeability. Longwall mining causes extensive, high‐reaching, well‐defined zones of stress, fracturing, and hydraulic impact, the maximum permeability increases being in the tensile zones immediately above the panel and at the sides of the subsidence trough. In shallow aquifers, permeabilities and ground‐water velocities increase, and hydraulic gradients decline independently of mine drainage.A study of a deep coal mine in the Appalachian Plateau, Pennsylvania indicated: probable hydraulic connections between the mine and shallow aquifers in a principal valley area; no obvious response of water levels in shallow aquifers to undermining by supported headings; and rapid, considerable declines in such water levels in response to nearby longwall mining. These results are consistent with the conceptual model.