Peripheral stability of circular tunnels in anisotropic undrained clay

Abstract

In the present analysis, solutions have been obtained for evaluating the minimum support pressure to be offered by means of lining for maintaining peripheral stability of circular tunnels constructed in clay taking into account anisotropic undrained shear strength parameters. The finite element approach based on lower bound theorem of limit analysis was implemented for performing the computations and second order cone programming technique has been applied for optimizing the magnitude of support pressure. The solutions obtained in this analysis can be used for computing the support pressure for tunnels driven in anisotropic normally consolidated (NC) or lightly over consolidated (LOC) clay for linear increase in undrained shear strength with depth, and anisotropic heavily over consolidated (HOC) clay where undrained shear strength remains constant with depth. The anisotropic shear strength of clay substantially influences the required support pressure, that is, the support pressure computed using anisotropy strength parameters has been found to be higher for tunnel driven in NC/LOC clay and lower or higher for tunnel driven in HOC clay than that determined on the basis of isotropic strength parameters.