Acoustic emission and strain energy release in the failure process of a circular tunnel surrounding rock at different pore pressures were modeled by using FLAC.A strain-softening constitutive relation was used and a tunnel was excavated after the model was loaded to reach a static equilibrium state.Numerical results showed that three kinds of failed element numbers in shear,tension and in both,and two kinds of released energies(due to shear and tensile failures) intermittently increased with the timestep.At...