Analysis of the mobilization of strength parameters in brittle intact rock

The At high-stress conditions in hard rock masses, the behavior of intact rock plays a major role in crack initiation and propagation, defining damage conditions around excavations. For modeling brittle rock behavior, the Cohesion-Weakening-Friction-Strengthening (CWFS) linear model has proven to be a good alternative for estimating the damage evolution around underground openings through the peak-residual values and the mobilization range defined as Critical Plastic Strain (CPS), however, it has not been extensively applied to intact rock at laboratory scale tests. Besides, the parameters of the CWFS model are usually difficult to obtain and are estimated indirectly from laboratory tests or from back-analysis of excavations that have presented brittle failure. This study uses a reliable optimization method to determine the CWFS model parameters for intact rocks to recreate its complete stress-strain curve, with a focus on post-peak behavior. Using this approach, the CWFS model parameters are estimated for an extensive database of six different hard rock types at different confining stress conditions, in order to analyze post-peak behavior. Results show that the obtained parameters for plastic strain-dependent mobilization of cohesion and friction are not fixed as supposed in other studies and depends on the lithology, furthermore its variation also depends on the initial values. CPS values also define the Drop Modulus parameter in brittle failure, which is discussed and compared with literature values. Guidelines for estimating the strength parameters mobilization can be concluded, including comparisons to usual intact rock parameters such as mi or UCS. Based on the implications of this study further development of strength mobilization models in hard rock masses is addressed and discussed.