A spatial strain localization mechanism of zonal disintegration through numerical simulation

The zonal disintegration is studied from a viewpoint of the spatial strain localization, a prospective idea to tackle the problem. The three-dimensional loading and unloading models are modeled numerically based on a strain-softening heterogeneous constitutive model. In the loading model, after a cylindrical tunnel is excavated, the displacement-controlled loading is conducted in the direction of the tunnel axis. However, in the unloading model, after the model has reached a static equilibrium state, a cylindrical tunnel is excavated step by step. In loading and unloading conditions, numerical results reveal that the zonal disintegration phenomenon that annular regions with high shear strains are isolated or divided by those with lower shear strains is existent. Compared with results in the loading model, results in the unloading model are even consistent with the field observations. At a plane orthogonal to the tunnel axis, the regions with higher shear strains, far away from the tunnel surface, are formed by propagation of shear bands that do not originate from the plane.