Mining subsidence in the concealed coalfields of north-east England
Subsidence profiles can be accurately predicted from empirical experience in the exposed coalfields, provided that the Coal Measures are comprised of weak shale strata. The predicted profiles for both vertical subsidence and horizontal strain are smoothly varying functions of surface position. Where thick beds of strong sandstone or limestone are present in the overburden, however, the subsidence behaviour can be quite different. The outcrop of the Permian Lower Magnesian Limestone in County Durham is deeply fissured above faults which bound multi-seam workings in the underlying Coal Measures. At Selby, in Yorkshire, where the Coal Measures are overlain by about 200 m of Permo-Triassic strata, subsidence due to individual longwall panels does not fully develop until the adjacent panels on both sides have also been worked. These phenomena can be understood in terms of the behaviour of relatively rigid blocks, separated by joints and bedding planes.