NUMERICAL SIMULATION OF THE STRAIN LOCALIZATION OF A CIRCULAR TUNNEL AT DIFFERENT ELASTIC MODULI

Strain localization processes of a circular tunnel at different elastic moduli are modeled by use of FLAC where the solution is based on equations of motion. In the present calculation, the tunnel is excavated after the model is loaded to reach a static equilibrium state. The numerical results show that at low and moderate elastic moduli, the movement of the surrounding rock toward the center of the tunnel is apparent once the tunnel is excavated, generating many fracture bands, V-shaped notches and shorter shear bands. The analyses and numerical simulations based on static equilibrium, which may yield unsafe solutions, cannot be applied to these cases. When the elastic modulus is lower, the capacity of the surrounding rock maintaining uniform circumferential or loop deformation is worse, and the axially-symmetrical deformation mode is easier to be broken and broken earlier. Although the failed number of elements is not monotonic with an increase of the elastic modulus, in general, as the elastic modulus is increased, the failed number of elements decreases, and the maximum shear strain increment is decreased monotonically and rapidly.