Abstract:

In many practical situations, for instance, in jointed rock mass, linear M-C yield criterion may not be justified and a nonlinear Hoek-Brown yield criterion would be more appropriate, so it is necessary to attempt to calculate deformation of tunnel by the criterion. The surrounding rock is divided into three zones: elastic zone, strain softening zone and plastic flow zone. Theoretical derivation on deformation is carried out by Hoek-Brown criterion and non-associated flow rule. Parameters of surrounding rock in strain softening zone are variable and they depend on the plastic deformation of this zone, so it’s difficult to derive the analytical solution for stress in this zone. Runge-Kutta method is used to carry out numerical calculation and the radiuses of strain softening zone and plastic flow zone are calculated. Finally, the deformations of tunnel are calculated. It is demonstrated by an example that the results calculated by the method in this paper and Carranza-Torres’s method are almost the same when strain softening zone and plastic flow zone are not be considered. Furthermore, it is demonstrated by the other example that dilation angle affects deformation more severely when in-situ stress becomes greater.

Key words: tunnel, Hoek-Brown criterion, strain softening zone, plastic flow zone, Runge-Kutta method