A Simple Approach for Circular Tunnels Excavated in Strain‐Softening and Dilatancy Rock Masses

ABSTRACT This study proposes a simple numerical approach that incorporates rock strain‐softening (SS) and dilatancy into the triple‐shear‐element unified strength criterion (TS‐USC). A parametric analysis is conducted to elucidate rock mass responses. The results demonstrate that the intermediate principal stress (IPS) enhances rock mass stability and limits plastic zone growth. The TS‐USC should be used with caution for tunnel stability evaluation because it may underestimate rock displacements. Dilatancy behaviors notably affect rock displacements but have minimal influence on plastic zone radius, radial stresses, and tangential stresses. Therefore, the dilatancy model needs to be chosen reasonably to achieve an acceptable accuracy level. Rock displacements at the excavation profile and the plastic zone radius increase approximately linearly under different SS behaviors. SS behaviors mainly affect tangential stresses; however, for a fixed SS behavior (i.e., for a given δ ), radial stresses at softening‐residual interface are minimally affected by supporting force. These factors deserve attentions during stability analysis and support system design.