Abstract:

Rockburst processes of a tunnel at different lateral pressure coefficients are modeled by use of FLAC. To model excavation, a FISH function is written and used to delete the elements in the tunnel. For rock elements exhibiting linear strain-softening behavior beyond the occurrence of failure and then ideal plastic behavior, the failure criterion obeys composite Mohr-Coulomb criterion with tension cut-off. The present calculation is divided into three steps. Firstly, the pressures in the horizontal and vertical directions are 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 at lower lateral pressure coefficients, dog-ear or V-shaped notches are generated in the surrounding rock that is stable after rockbursts. At moderate lateral pressure coefficients, V-shaped and U-shaped (panlike) notches are observed one after the other and the surrounding rock is still stable after rockbursts. When the lateral pressure coefficients are higher, the V-shaped notches are firstly generated and then the U-shaped notches are formed; afterwards, shear bands intersect and scalelike failed zones are formed above the roof and below the floor, leading to the unstable failure of the surrounding rock. However, no failed zones are formed at the two sides of the tunnel.

Key words: circular tunnel, rockburst, shear band, V-shaped notch, U-shaped notch, scalelike failed zone, lateral pressure coefficient