A new continuum-based constitutive model for the simulation of the inherent anisotropy of Opalinus clay

Abstract

Opalinus clay has been extensively investigated, as it is considered as potential host rock for underground nuclear waste repositories. The behavior of the Opalinus clay is a transverse isotropic possessing anisotropic characteristics in both strength and stiffness. Also, the lab investigations conducted on the Opalinus clay found that it behaves as bi-linear elasto-plastic strain softened material in general and as brittle plastic in particular. Two case studies of tunnel excavated in shaly facies formation of the Opalinus clay have been numerically analyzed by applying a new continuum-based constitutive model called “Transubi model” providing an Instantaneous hydromechanical coupling short-term simulation by generating the pore pressure considering no fluid flow. Lab test results obtained from literature have been used to validate this model: triaxial experiments and direct shear tests. The Transubi model is able to duplicate the pre-yield hardening and the post-yield softening for loading perpendicular and parallel to bedding planes, S- and P- samples, respectively. Finally, two in-situ tests in the Mt. Terri URL are used to demonstrate the applicability of the Transubi model to predict the short-term hydro-mechanical coupled behavior. The results from numerical simulations for both excavations are compared to those from field observations showing better agreements than other previous numerical analyzes from literature.