A sensitive analysis on Mohr-Coulomb and Hoek-Brown parameters effective in ground response curve

Figure 1 shows a circular tunnel is excavated in a continuous, homogeneous, isotropic, initially elastic rock mass subjected to a hydrostatic stress po. The tunnel surface is subjected to an internal pressure pi. As pi is gradually reduced, the radial displacement occurs and a plastic region develops around the tunnel when pi is less than the initial yield stress.