Failure zone distribution and energy liberation in the surrounding rock of a circular tunnel at different post-peak brittleness are modeled by using of FLAC.A strain-softening constitutive relation is used and a tunnel is excavated after the model is loaded to reach a static equili-brium state.Numerical results show that for more brittle rock

the number of failed elements in the surrounding rock is greater;the released elastic strain energy is higher;and the equilibrium of the surrounding rock after the tunnel excavation is later.Although some loop failure zones are observed in some examples

these zones are not believed to be related to the zonal disintegration phenomenon.It is difficult to study the zonal disintegration phenomenon using the two-dimensional slip lines or failure characteristic lines.For investigating the zonal disintegration phenomenon

we can use the three-dimensional continuous medium model based on the spatial strain localization viewpoint

or we can use the two-dimensional model including granule

in which interactions among granule exist.These two methods introduce new factors that are absent in the two-dimensional continuous medium model.