Constitutive Behaviour of Brittle Layered Rocks Using a 3D Anisotropic Hoek and Brown Model



The history of geological deposits is often characterized by complex processes which strongly modify the mechanical behavior of rock masses. The intrinsic orientation-dependent properties connected with the presence of bedding planes induces anisotropic characteristics in the rock masses. In order to model their mechanical behavior, a 3D Hoek & Brown (HB) yield criterion has been used to introduce material symmetries through cross anisotropic elasticity and by means of the Uniaxial Compression Strength (UCS) expressed as a function of the bedding plane inclination. The material degradation and the resulting brittle mechanisms are simulated with a softening rule aimed to introduce a decreasing evolution of the Hoek & Brown parameters, thus enabling to model the post-peak behavior of the intact rock, as well as its non-linear dilation trend. This constitutive framework has been employed to evaluate the influence of preferential directions on the failure process by solving plane strain compression tests in PLAXIS 2D in which a viscous regularization technique is implemented to avoid the pathological mesh-sensitivity of the numerical solution during the formation and propagation of shear bands.