Finite element modelling of time dependent fracture with applications to the failure of rock around underground openings for nuclear waste disposals

A time-dependent progressive damage model for granite rock failure prediction that bridges the gap between the commonly adopted smeared and discrete approaches is formulated and implemented into the finite element program SIMEX. The extent of fracturing in the rock mass is simulated via a strain softening material description based on the overstress model of Perzyna. In addition, a limit-strain criterion is furnished to model the ultimate loss of carrying capacity of the rock. The SIMEX program is also modified to account for geometrically nonlinear behavior for problems involving large deformations.;The model has successfully predicted the evolution of inelastic deformation and associated stress fields responsible for the two prominent failure mechanisms: exfoliation (originally identified by Lajtai) and shear-banding. While cracking is found to be instantaneous, stress redistribution takes place over a relatively short period of time following excavation.;An initial parametric study predicts a stable behaviour of the rock structure in time. Further study is necessary to incorporate the three-dimensional nature of the problem, investigate possible bifurcation of the solution and experimentally verify the material characteristics adopted for this study.