Visualizing the full-field stress and plastic zones in arch tunnel surrounding rocks embedded with roadway-scale discontinuities using 3D printed transparent models and stress freezing techniques

Embedded roadway-scale discontinuities present significant risks to the safety of underground tunnels. Their effects on the stress distribution, plastic zone development, and failure behavior must be systematically analyzed for optimizing the tunnel design and support systems. However, accurately quantifying the full-field stress and visualizing failure processes in 3D tunnels through laboratory experiments and numerical simulations remains challenging. This study proposes a novel experimental system that integrates 3D printing, stress-freezing, and digital photoelasticity techniques to address the challenges associated with the preparation of structurally complex tunnel models, quantitative analysis of stress and plastic zones, and visualization of failure behaviors. The 3D experimental results indicate that the embedded structural plane exhibits considerable stress localization and blocking effects. The stress concentration and plastic zones are primarily located at the structural plane ends and on regions far from the structural plane. Furthermore, the presence of the structural plane significantly alters the failure mode of the tunnel, presenting pronounced regional failure characteristics. The 3D experiments in this study consider the influence of the model thickness direction and structural plane effects, which are typically neglected in simplified 2D analyses. Consequently, more realistic insights into the distribution and evolution of stress, plastic zones, and failure behaviors within tunnels are obtained. The mechanisms and principles realized through these laboratory experiments present new perspectives for optimizing and further improving the tunnel design and support systems. Furthermore, they present a scientific basis and valuable reference for subsequent numerical simulations of engineering-scale, structurally complex tunnel systems.