The geology of Castlefields Mine, Dudley, and its effect on the stability of the mine roof

Abstract

Abstract The mining of the Wenlock Limestone, which has taken place in the West Midlands during the last two hundred years, has resulted in a long and continuing history of subsidence and crownhole formation in a mainly urban area. In 1983, as part of a major study of the abandoned limestone mines, a programme of micro-seismic emission monitoring of rock falls and of rock paste infilling trials was started at the Castlefields Mine near Dudley. The mine is in Upper Wenlock Limestone with an overburden of approximately 22 m comprising about 1.5 m Passage Beds overlain by Lower Ludlow Shale. A number of stages of instability were observed, ranging from initial slabbing failure of the Passage Beds to extensive upward void migration through the Lower Ludlow Shale to within a few metres of the surface. The pattern of joints, and their condition, plays an important role in controlling the instabilities in a mine. Five joint sets, with varying degrees of dilation, movement and infilling, were identified in a survey of structural discontinuities in Castlefields Mine. One master joint set, characterized by uneven dilation and clay infilling, was found to exert a major influence on the position and development of roof instabilities within the mine. In this paper, the lithology, geological and mining history and structure of Castlefields Mine are described and their influence on mine stability discussed.