A rheological constitutive model for damaged zone evolution of a tunnel considering strain hardening and softening

A rheological constitutive model for damaged zone evolution of a tunnel is proposed in this paper to describe the strain hardening and softening properties of the excavation-disturbed rock mass. Firstly, the one-dimension rheological model is introduced by connecting the improved St. Venant body with the Nishihara model, and this model can be used to describe the whole process including transient viscoplastic creep under a low-stress state, steady-state and accelerative creep under a high-stress state. Secondly, the constitutive equations of the rheological model under three-dimensional condition of the improved St. Venant body based on generalized plasticity potential theory are deduced, and the generic three-dimensional rheological model is developed. Thirdly, the creep and stress relaxation properties of the rheological model are studied and discussed. Furthermore, numerical analysis of triaxial compression tests and triaxial compression creep tests are conducted and the rheological model are validated. The results show that the rheological model can be used to study the evolution of excavation damaged zone in underground tunnel engineering.