The U.S. Bureau of Mines presents an application of the discrete element method to simulate fracture propagation in a coal mine entry roof using a discrete element code termed decice. A simple rock bolt model is implemented to show the benefits of bolting to increase the resistance to shearing and separation along horizontal bedding planes to maintain roof stability. Roof failures are common in coal mines where the immediate roof is often comprised of thin shale laminae exposed to adverse in situ stress conditions. Conventional numerical techniques, such as finite element and boundary element methods, have been used to analyze the stresses and deformations leading to such problems. However, their application becomes severely limited once the roof rock fractures and behaves as a discontinuum. The discrete element method readily lends itself toward modelling fractured discontinuous material. A discrete element analysis was conducted of a coal mine entry consisting of horizontally bedded roof strata subjected to vertical and horizontal in situ stresses of 7 mpa (1,000 psi) and 3.5 Mpa (500 psi), respectively. Results show that for the case where no rock bolts are used, shear fracturing propagated nearly vertically upwards through the horizontal roof beds as lower beds collapsed downwards, transferring stress to the next higher member. When the analysis was rerun with the inclusion of rock bolts, the fracturing again initiated near vertically, but ceased as the roof bolts prevented separation along bedding planes, thereby creating a stronger roof member. Future analysi
1st U.S. Conference on Discrete Element Methods, Golden, Colorado, Oct 19- 20, 1989, 9 PP.