Discrete element modeling of tool-rock interaction II: rockindentation

The failure mechanisms induced by a wedge-shaped tool indenting normally against a rock surface are investigated using the discrete element method (DEM). The main focus of this study is to explore the conditions controlling the transition from a ductile to a brittle mode of failure. The development of a damage zone and the initiation and propagation of a brittle fracture is well captured by the DEM simulations. The numerical results support the conjecture that initiation of brittle fractures is governed by a scaled flaw length, a ratio between the flaw size lambda and the characteristic length l = (K-Ic/sigma(c))(2) (where K-Ic is the toughness and sigma(c) the uniaxial compressive strength). The size of the damage zone agrees well with analytical predictions based on the cavity expansion model. The effects of a far-field confining stress and the existence of a relief surface near the indenter are also examined. Copyright (C) 2012 John Wiley & Sons, Ltd.