In the user-defined constitutive model considering tension cut-off

nonlinear yield criterion and influence of confining pressure on elastic modulus

the failure behavior of the circular tunnel surrounding rock was modeled using two shapes’ grids with different constitutive models and loading conditions.In the first kind of grid（radial grid）

an ideal elastoplastic constitutive model was used and a circular tunnel is excavated before the model is loaded to an equilibrium state in numerical simulation.In the second kind of grid（rectangular grid）

an elastic-brittleplastic constitutive model was used and a circular tunnel is excavated after the model is loaded to an equilibrium state in numerical simulation.The results show that in the first kind of grid

the strain

displacement

plastic zone and the peak value of hoop stress of monitored elements are lowered as the elastic modulus is influenced increasingly by the confining pressure

and the differences of results based on the different constitute models appear gradually;in the second kind of grid

four symmetric V-shaped notches are found as the elastic modulus is influenced slightly by the confining pressure.The number and the size of V-shaped notches decrease significantly as the elastic modulus is influenced increasingly by the confining pressure.This phenomenon can be explained by the results in the first kind of grid.