Radial stress gradient effects on rockburst failure in tunnels: A 3D polycrystalline discrete element simulation study

Rockburst represents a highly destructive geological hazard in tunnel engineering, and elucidating its underlying mechanism is critical for effective hazard mitigation. This study investigates the influence of radial stress gradient on the multivariate catastrophic information responses associated with tunnel rockburst. A three-dimensional polycrystalline discrete element numerical analysis method was established based on three-dimensional block discrete element theory and a polycrystalline modeling system. Using an independently developed numerical approach and a customized stress path, the catastrophic processes of rockburst, acoustic emission (AE) signal characteristics, and energy evolution were systematically analyzed under varying radial stress gradients, and the governing mechanisms were further examined. The results indicate that rock specimens consistently experienced rockburst failure of varying intensities under radial stress gradients of 20, 50, and 80 kPa/mm. Characteristic stress increased with rising radial stress gradient, exhibiting a pronounced radial stress effect. The strengthening effect imparted by the radial stress gradient led to higher peak stresses in the rockburst samples. The failure processes observed in numerical simulations closely matched those from laboratory tests, which could be summarized as a progressive sequence: localized particle ejection, slab splitting, slab fracturing into blocks, and complete ejection of these blocks. A competitive evolution mechanism between elastic strain energy and dissipation energy was evident throughout the energy evolution process of rockburst. As the radial stress gradient increased, the failure mode of the rock samples gradually transitioned from tensile failure to shear-tensile failure. The formation mechanism of rockburst was categorized into three progressive stages: tensile failure, shear failure, and tensile-shear Radial stress gradient effects on rockburst failure in tunnels: A 3D polycrystalline discrete element simulation study Received: 23-Dec-2025 1st Revision: 26-Feb-2026 2nd Revision: 17-May-202 composite failure. Based on their failure characteristics, rockbursts were further classified into two types: rupture-stripping and burst-ejection. The findings of this study have significant implications for early warning and preventive control of rockburst hazards in tunnel construction.