3 - Numerical Modeling of Yield Zones in Weak Rock

Abstract

This chapter discusses numerical modeling of yield zones in weak rock. Weakened or partly fractured materials can be modeled by a linear elastic material with a low modulus of elasticity. The major difficulty in the numerical modeling of geological materials is in the determination of the input parameters. Results of laboratory tests for such parameters as the modulus of elasticity and Mohr–Coulomb or Hoek–Brown failure properties are not always relevant to the rock in situ. Equivalent elastic properties of a weakened or yielded rock can be related, via the deformation theory of plasticity, to failure and postfailure properties such as pre-and postfailure cohesion and angle of friction of the rock. A major advantage of the deformation theory is ease of computation. The formulation is done in such a way that an iterative procedure can be set up with a linear elastic finite element program. In the incremental theories, the boundary tractions are reduced in increments until the material adjacent to the opening yields.