| A non-linear constitutive model with tension cut-off is developed by use of C++based onMohr-Coulomb constitutive model in FLAC. For stresses and displacements of monitoredelements or nodes, comparison is conducted between the numerical solutions (includingsolutions based on Hoek-brown constitutive model, Mohr-Coulomb constitutive model anddefined non-linear constitutive model) and the analytical solutions (based on Hoek-Brownconstitutive model). Validation of the defined non-linear constitutive model is verified. Strainlocalization of the surrounding rock of a circular tunnel is modeled using the definedelastic-brittle-plastic constitutive model. The tunnel is excavated after the model is loaded to anequilibrium state. On the condition of symmetric boundary conditions of computational modeland homogeneous constitutive parameters, four symmetric V-shaped notches are found, as isconsistent with observations in situ and experimental results of rockbursts in a hydrostaticpressure.Influence of the critical stress in the defining constitutive model corresponding to thetangential point of linear and nonlinear yield functions on numerical results is a key problem.Results show that the plastic zone radius, the shear strain increment of monitored elements andthe displacement of monitored nodes decrease and the stresses of the monitored elements in theplastic zone increase as the absolute value of the critical stress increase, which is due to theincrease of yield limit in the linear shear yield part.In the user-defined constitutive model, the elastic modulus dependent on the confiningpressure is considered. Failure behavior in the circular tunnel surrounding rock is modeled usingtwo different grids (radial grid and rectangular grid), constitutive models and loading conditions.In the first grid, the strain, displacement, plastic zone and the peak value of hoop stress ofmonitored elements are lower as the elastic modulus is influenced greatly by the confiningpressure; in the second grid, four symmetric V-shaped notches are found as the elastic modulus isinfluenced slightly by the confining pressure. The number of V-shaped notches decreasessignificantly as the elastic modulus is influenced greatly by the confining pressure. Thisphenomenon can be explained by the results in the first grid. |
