Dimensionless charts for the GRC for rock masses exhibiting strain-softening behaviour

A dimensionless graphical representation based on a self-similar numerical solution (Alonso et al. 2003) for Ground Reaction Curve (GRC) for tunnels excavated under hydrostatic loading, strain-softening rock mass behaviour, Mohr-Coulomb failure criterion and non associated flow-rule is presented in this paper. The rock is assumed to behave as a strain-softening manner and the transition from elastic to residual stage is governed by the slope of the softening stage -or drop modulus, denoted by M-. The solution is based on the assumption that after the intact strength of the rock is exceeded, the material loses cohesive and frictional strength in a similar proportion, as dictated by a "strength loss" parameter (beta) (Carranza-Torres et al. 2002). This parameter quantifies the jump of strength from the intact condition to the residual one, and it is defined within the range 0% < beta < 100%. beta = 0% implies no loss of strength (perfect plastic behaviour) and beta = 100% implies that both residual friction angle and cohesion are null. This assumption allows certain terms to be dropped out of the formulation, resulting in a considerable simplification of the problem (Agnasnostou & Kovari, 1993). In this work, the dimensionless charts are represented for a given value of Poisson's ratio, peak friction angle, peak cohesion, dilatancy angle and stress field. For each value of parameter beta (in the range 0% < beta < 100%.), a branch of GRC is represented for different values of "drop modulus" indicating the transition from a perfectly brittle to perfectly plastic behaviour.