Physical and numerical investigation on nonlinear mechanical properties of deep-buried rock tunnel excavation unloading under complicated ground stresses

Abstract

The nonlinear stress and deformation response of tunnel excavation unloading under high and complicated geostresses are important features of deep rock tunnel engineering, and such conditions differ significantly from those of shallow tunnels. Additionally, several studies on deep tunnels have focused on mechanical behaviors of rock tunnels at certain depths, ignoring nonlinear responses of rock tunnels at various depths. In this study, physical model tests and three-dimensional (3D) numerical calculations concerning complicated ground stresses were conducted to investigate the nonlinear mechanical and strength properties of tunnels excavated in rock formations with varying buried depths. The generalized Zhang–Zhu criterion (GZZ) was found to appropriately describe the nonlinear laws of rock strength (yield) with stress levels on the π plane, and the correctness and reliability of the GZZ strength criterion were subsequently verified by comparing the deformation monitoring data of physical model testing with different strength criteria-based numerical results. These results were then used to examine the stress distributions, deformations, and failure characteristics of physical model tunnels under complicated stress conditions at various buried depths. The nonlinearity of stress and deformation of the model tunnels are directly related to stress conditions, especially to the horizontal tectonic stress. This indicates that the traditional linear design approaches and practical experiences related to shallow tunnels dominated by gravity stress are not applicable to deep-buried tunnels under high and complicated ground stress conditions.