When a tunnel or an underground structure is excavated in deep geological environments, the failure process is affected and eventually dominated by stress-induced fractures growing preferentially parallel to the excavation boundary. This fracturing is generally referred to as brittle failure by spalling and slabbing. Continuum models with traditional failure criteria such as Hoek-Brown or Mohr-Coulomb model have not been successful in prediction of the extent and depth of brittle failure. The cohesion weakening and frictional strengthening (CWFS) model is known to predict brittle failure well. The general conditions (General, Porous and Time Dependent) are same with Mohr-Coulomb model, but the hardening/softening behavior with table using Mohr-Coulomb yield surface can be considered in the nonlinear parameters.

[Nonlinear Parameters]

[Mobilisation of the strength components]