Strain localization processes of a tunnel at different cohesions are modeled using FLAC.To model the tunnel excavation

a FISH function is written and used to delete the elements in the tunnel.Rock elements exhibit linear strain-softening behavior beyond the occurrence of failure and then ideal plastic behavior.A composite Mohr-Coulomb criterion with tension cut-off is used.The present calculation is divided into three steps.Firstly

a hydrostatic pressure is applied to the plane strain model until a static equilibrium state is reached.Secondly

the tunnel is excavated using the written FISH function.Thirdly

the calculation renews to achieve a new equilibrium state or a plastic flow state.Results show that as cohesion decreases

the failure modes of the tunnel surrounding rock firstly changes from minor local failure in tunnel surface to shear failure in four smaller symmetric V-shaped rockburst notches and then from shear failure in bigger V-shaped rockburst notches comprising smaller notches to entire section collapse due to longer shear band intersection.For the former three failure modes

the surrounding rock can sustain its stability after rockbursts.Compared with the maximum tensile strain

the maximum shear strain increment and plastic shear strain are higher and the values of the maximum shear strain increment and plastic shear strain are closer.As cohesion increases

the three kinds of strains decrease.