ABSTRACT
Analyzing the complex mechanical problem of the advance of a deep tunnel by means of numerical methods requires appropriate constitutive models of the interacting materials to obtain reliable estimates of displacements and stresses of the support structure. A recently proposed damage plasticity model for rock mass is employed in finite element simulations of a deep tunnel, driven by a drill, blast, and secure procedure according to the New Austrian Tunneling Method. The model describes the nonlinear three-dimensional mechanical behavior of intact rock and is extended to model quasi-homogeneous, quasi-isotropic rock mass based on the geological strength index and the disturbance factor. In contrast to linear-elastic perfectly-plastic models, which are commonly used in practical applications, irreversible strains in the pre-peak region and degradation of stiffness and strength are represented. The numerical results based on the damage plasticity model for rock mass are compared with numerical results on the basis of a perfectly-plastic rock model and with available in-situ measurement data. Consideration of strain softening in the damage plasticity model for rock mass allows the prediction of the formation of shear bands emanating from the tunnel surface due to excavation. The obtained localized deformation zones indicate the transition of the rock mass from a quasi-continuum to a quasi-discontinuum, which can be interpreted as a precursor to failure of the rock mass.
