ANISOTROPIC FAILURE CRITERION FOR AN ARGILLACEOUS ROCK: FORMULATION AND APPLICATION TO AN UNDERGROUND EXCAVATION CASE

A cross-anisotropic extension of an elastoplastic constitutive model is described, based on a non-uniform scaling of the stress tensor. The Mohr-Coulomb yield condition is employed, although this concept can be applied to any other stress-based criterion. It has as main advantage the possibility of being incorporated into an already implemented constitutive model with only minor modifications. The resulting constitutive model has been applied to the coupled hydromechanical simulation of an excavation of a horizontal tunnel in the underground research laboratory at Bure (France). The orientation of the tunnel ensures that the transverse in situ stress state is nearly isotropic. The tunnel excavation has been intensely monitored and the nature and extension of the damaged zone have been studied by a variety of field techniques. It is shown that the analysis performed using the elastoplastic model incorporating the anisotropic failure criterion is able to reproduce the observed geometry of the damaged zone. The anisotropy of displacement measurements is also matched satisfactorily.