Numerical analyses of shear bands failure in tunnel excavation problems using a regularized Hoek-Brown model

This paper discusses some numerical analyses performed with a generalized three-dimensional Hoek & Brown (HB) model which strength criterion has been considered to simulate the mechanical behavior of rocks in brittle conditions. For this purpose, this constitutive framework has been enhanced with hyperbolic softening and non-linear dilation, thus enabling to investigate failure modes in the form of dilating shear bands. To restore the objectivity of the numerical solution during the development of localized strain, a viscous regularization technique has been employed to simulate localization phenomena in two different initial boundary value problems, both computed by using the finite element software PLAXIS 2D: (i) a biaxial test, and (ii) a tunnel excavation problem simulated through a deconfinement process. While the former has been considered to test the effect of the viscous parameter in governing the structural behavior of the rock sample, the latter has been selected to model the shear bands propagation during the process of a tunnel excavation in which the rocks mass has been characterized by different mechanical properties. The computed solutions have been compared with existing formulations based on the framework of HB strength criteria, thus enabling to further validate the implementation of the proposed constitutive equations.