Numerical simulation study on failure mechanism of deep soft-weak tunnel considering surrounding rock deterioration

The user developed flow-chart of the degradation damage constitutive model in FLAC 3D and the selection of mechanical parameters for soft-weak surrounding rock were introduced, and numerical simulations were studied for the damage and failure mechanism of a double-track high speed railway deep tunnel in rock of class IVand V according to the railway tunnel code of China. The stress in rock mass was analyzed so as to define the pressure arch boundary, and the influences on the stress distribution zone by factors like tunnel depth, the lateral pressure coefficient, the level of the surrounding rock, etc., were studied through numerical simulations. The results indicate: (1) The FLAC 3D degradation damage constitutive model can be used to describe the extent and depth of the excavation damage zone, which reveals that the unstable region of the surrounding rocks is situated at the shearing wedge along the minimum principal stress; (2) After excavating a deep tunnel, excavation damage zone, pressure arch, and original stress zone exist in sequence outside the tunnel wall. (3) Tunnel depth, the lateral pressure coefficient and the class of the surrounding rock greatly influence the scope of the stress distributions.