Structure-type rockburst in deep tunnels: Physical modeling and numerical simulation

Structure-type rockbursts frequently occur in deep tunnels, with structural planes and stress conditions being critical factors in their formation. In this study, we utilized specially developed analogous materials that exhibit the high brittleness and strength characteristics of deep hard rock to construct physical models representing different types of structural planes, including composite, exposed, non-exposed, and throughgoing structural planes. Physical simulation experiments were conducted on structure-type rockbursts in deep horseshoe-shaped tunnels, focusing on strain differentiation characteristics, critical triggering conditions, critical crack opening displacement, the incubation process, the reduction effects of structural planes on failure intensity, and formation mechanisms. These experiments were complemented by acoustic and optical monitoring, as well as discrete element numerical simulations, to provide a comprehensive analysis. The results revealed that the most significant strain heterogeneity in the surrounding rock occurs at the tip of the structural plane along the tunnel's minimum principal stress direction, driven by the combined effects of tensile and shear forces. We quantitatively determined the critical stress and strain conditions for structure-type rockbursts and evaluated the intensity of rockbursts induced by different structural planes using critical crack opening displacement (COD) values, the uniformity coefficient, and the curvature coefficient. Analysis of acoustic emission events, including frequency, amplitude, and b -value, indicated that the macro-fracture process is governed by both the principal stress differential and the characteristics of the structural plane. Furthermore, using the bearing capacity reduction coefficient, we found that exposed structural planes have the most significant weakening effect on rock mass strength, followed by non-exposed and throughgoing structural planes. The analysis of average frequency (AF) and rise angle (RA) parameters revealed a close correlation between the failure modes of structure-type rockbursts, the rock mass structure, and the stress levels. These findings provide critical theoretical support for the prediction and prevention of structure-type rockburst disasters.