ABSTRACT
When modelling large scale boundary value problems in rock material; such as around underground coal gasification cavities, it is essential to consider the effect of discontinuities in the rock mass on the modelled system response. Such discontinuities can include bedding planes, small scale fracturing and large scale faults, with sizes ranging from a few centimetres to hundreds of metres. It is often impossible to precisely determine the jointing pattern in-situ as many attempts to do so (e.g. excavation) inevitably destroy that pattern. Empirical measures such as the geological strength index (GSI) (Hoek & Brown, 1997, Marinos & Hoek, 2000) are often used to account for the effect of joints by reducing material properties used in continuum models. Such methods allow for the overall impact of jointing to be considered but do not resolve any effects due to the spatial positioning or orientation of these joints. The distinct element method (DEM) provides an incredibly useful tool for modelling such systems by representing rock masses as a collection of discrete rock blocks separated by joints (discontinuities) with defined frictional and elastic properties. Simulating a jointed rock mass with the distinct element method requires an appropriate selection of model geometry and material parameters, not just of the rock material itself but also of the rock joints.
