Equivalent Mohr-Coulomb dilation parameter for Hoek-Brown rock

In the analysis and design of underground excavations in rock, the conventionally used linear Mohr-Coulomb (M-C) failure criterion is generally not valid and it is more appropriate to use the non-linear Hock-Brown (H-B) failure criterion. However, most of the analysis techniques and software are presently based on the M-C criterion. Therefore, it has been of interest to obtain a correlation between these two failure criteria to allow the H-B criterion to be used conveniently. The existing methods of obtaining the equivalent M-C parameters (cohesion and angle of internal friction) assume the plastic flow rule to be linear and corresponding to the M-C criterion.; The proposed novel method developed in this thesis in order to calculate the M-C equivalent dilation parameter, is based on non-linear flow rule compatible with the original and the generalized H-B criteria. The method is based on an analytical solution developed for displacements around a circular opening in a dilating (plastic volume change due to shear) rock mass subjected to a hydrostatic in-situ stress field, where dilation is considered to be variable. The rock mass is considered to be elastic-perfectly-plastic and the elastic-brittle plastic behavior is treated as a special case. The effectiveness of the proposed method is demonstrated by analyzing some example problems using the finite element method. Finally, the method was expanded for non-circular openings subjected to non-hydrostatic stress fields.