Optical quantification and characterization of 3D stress fields and plastic zones around arch tunnel models using stress freezing and 3D printing techniques

Accurate characterization and quantification of the three-dimensional (3D) stress field and plastic zones around tunnels are vital for predicting potential rock bursts and spalling disasters and providing a quantitative basis for rational support design. However, the 3D stress field and plastic deformations around tunnels cannot be easily quantified experimentally because of the limitations of conventional experimental techniques. In this study, a novel experimental method combining photoelastic stress-freezing, phase shifting, and phase unwrapping techniques was proposed to quantitatively characterize the principal stress difference and shear stress around an arch tunnel model fabricated using 3D printing. The plastic deformation zones and elastoplastic boundaries around the tunnel were quantitatively defined using the Tresca yield criterion and stress-optic law. The experimental results obtained by the proposed method were compared with the simulation results of the 3D stress and plastic deformations around the tunnel. The results indicated that the areas with high stresses were primarily located at the corners, sidewalls, and shoulders of the arch tunnel. The sidewalls are stress disturbance zones, whereas the top and bottom are rapidly changing stress zones, indicating that disasters are prone to occur in these areas. Plastic zones were formed primarily at the sidewalls, corners, and shoulders of the tunnel, and the entire morphology exhibited a butterfly shape. The proposed method demonstrates good potential for validating numerical solutions. This study contributes to the understanding of the failure mechanisms of underground tunnels and enhances the prediction and prevention of tunnel disasters.