Model experiments and numerical analysis of the influence of tunnel diameter on tunnel rockburst

With the increasing development of deep-buried engineering projects, rockburst disasters have become a frequent concern. Studies have indicated that tunnel diameter is a critical factor influencing the occurrence of rockbursts. To investigate the influence of tunnel diameter on the deformation and failure characteristics of surrounding rock, large-sized rock-like gypsum specimens were tested using a self-developed true triaxial rockburst loading system containing circular tunnels with three different diameters (D = 0.07 m, 0.11 m, and 0.15 m). Acoustic emission monitoring, together with a miniature intelligent camera, was employed to analyze the entire process, focusing on macroscopic failure patterns, fragment characteristics, and underlying failure mechanisms. In addition, theoretical analyses were carried out and combined with numerical simulations to investigate the differences in energy evolution associated with rockburst physical models. The results indicate that: (1) The rockburst process with different tunnel diameters consistently evolved through three distinct stages—initial particle ejection, crack propagation accompanied by flake spalling, and, finally, fragment ejection leading to the formation of a 'V'-shaped notch. (2) Increasing tunnel diameter reduces rockburst failure load while increasing surrounding rock damage extent, total mass and average size of ejected fragments. Additionally, shear failure proportion decreases with tensile failure becoming increasingly dominant. (3) Larger tunnel diameters reduce the attenuation rate of elastic strain energy, thereby expanding the zone of elastic strain energy accumulation and disturbance and creating conditions for larger volume rockburst. (4) Larger tunnel diameters result in a smaller principal stress ratio at equivalent distances in the surrounding rock, indicating a higher likelihood of tensile failure. (5) Numerical analyses further reveal that larger tunnel diameters reduce the maximum elastic strain energy density around the tunnel, lowering the energy released per unit volume of rockburst fragments and their ejection velocities. However, both the total failure volume and overall energy release from rockburst increase. Model experiments with different tunnel diameters are of great significance for optimizing engineering design and parameter selection, as well as guiding tunnel construction under complex geological conditions.