Influence of tunnel excavation on the magnitude and rotation angle of principal stress in surrounding rock.

The stress disturbances induced by deep tunnel excavation are a key factor leading to the instability and failure of surrounding rock. To investigate the stress evolution in surrounding rock, this study utilizes a physical simulation system for deep caverns to replicate the actual excavation process of tunnels. The study quantitatively analyzes changes in the magnitude and orientation of surrounding rock stresses, and validates the experimental results through numerical analysis. The study revealed that: (1) In elasto-plastic tests, the trajectories of the principal stress axes at the vault and bottom are symmetrical about the XZ plane, whereas in elastic tests, they exhibit symmetry about the origin. (2) The experimental and numerical simulation results of the principal stress axis evolution at four key monitoring points (vault, shoulder, waist, and bottom) are consistent. Using FLAC3D, the regions between these points were further divided, identifying seven distinct regions of surrounding rock, each characterized primarily by one of the four representative patterns, with the shoulder region acting as a transitional zone. (3) Regardless of whether the surrounding rock is in an elastic or elasto-plastic state, the evolution of the principal stress magnitudes and their angles with the coordinate axes remained entirely consistent.