The impact of porosity and crack density on the elasticity, strength and friction of cohesive granular materials: Insights from DEM modelling

This study uses the Discrete Element Method (DEM), in which rock is represented by bonded, spherical particles, to investigate the dependence of elasticity, strength and friction angle on porosity and crack density. A series of confined triaxial extension and compression tests were performed on samples that were generated with different particle packing methods, characterised by differing particle size distributions and porosities, and with different proportions of pre-existing cracks, or uncemented particle contacts, modelled as non-bonded contacts. The 3D DEM model results demonstrate that the friction angle decreases (almost) linearly with increasing porosity, and is independent of particle size distribution. Young's modulus, strength and the ratio of unconfined compressive strength to tensile strength (UCS/T) also decrease with increasing porosity, whereas Poisson's ratio is (almost) porosity independent. The pre-eminent control on UCS/T is, however, the proportion of bonded contacts, suggesting that UCS/T increases with increasing crack density. Young's modulus and strength decrease, while Poisson's ratio increases with increasing crack density. The modelling results replicate a wide range of empirical relationships observed in rocks and underpin improved methods for the calibration of DEM model materials. (C) 2008 Elsevier Ltd. All rights reserved.