Deformation properties of a sub-bituminous coal mass

Abstract

Process simulation tests have been carried out to investigate the relative importance of various time-dependent processes on the deformation behaviour of tunnels in weak rock or at large depth. Back analysis of loading and unloading tests on two large coal specimens before and after excavation of a tunnel yielded values for the elastic parameters. The results show that the elastic parameters of the coal tested are relatively insensitive to pressure (between 3 and 10 megapascals), and that a typical Poisson's ratio lies between 0.3 and 0.4 for loading parallel to the bedding plane and less than 0.1 for loading perpendicular to the bedding. The bulk and Young's moduli vary widely within a relatively small area. Very few rock types exhibit such variation in deformation properties on the same scale, and this should be recognised when testing coal or designing structures in or on coal.