Summary - Modern coal-winning techniques require identification of panels of coal in which seam geometry irregularities are minimal. The locations and throws of faults in unworked ground can often be determined by the projection of faults recorded in earlier workings. Successful projection requires a knowledge of the systematic geometry of faults in respect of throw variation on the fault surface and of the shape and dip of the fault surface. A simple geometrical model of an ideal single normal fault is described in which the throw varies systematically from a maximum at the centre of the elliptical fault surface to zero at the tip-line, or edge, of the fault surface. A fault surface ellipticity of 2, with a horizontal major axis, and a dip of 70 degrees are recommended as approximations when no other data are available. Successful lateral projection of faults within a seam, or vertical projection from higher or lower seams, depends on the amount and type of data available from earlier workings and also on the accuracy of recorded throw values which are sometimes less than the total throw.
Retrospective studies of vertical projection of faults using a Throw Profile Plot, at Royston colliery, Yorkshire, and of a lateral projection of a fault at Markham colliery, Derbyshire, are described. Discontinuous fault trace arrays are common and represent a systematic departure from the ideal single fault model. Discontinuous fault trace arrays can be treated as single faults if the throws on overlapping segments are summed. Examples of the summing of throws on overlapping fault trace segments are described from Nook colliery, Lancashire, and Cotgrave colliery, Nottinghamshire.
The new projection methods are intended to increase the probability
of successfully delineating economically workable panels of coal before
significant development costs are incurred.
Proceedings of the Yorkshire Geological Society 48,
209-219, 1990.