This study utilized the combined finite-discrete element method (FDEM) to investigate the stability and fracture evolution mechanisms of surrounding rock in bias tunnels within layered rock masses. Firstly, an improved constitutive model for cohesive element incorporating irreversible damage is proposed and the numerical model is rigorously validated against a physical model test, with results exhibiting remarkable consistency in both fracture patterns and surface displacements. Subsequently, a systematical parametric study was performed, and the effects of bedding dip angle, bedding spacing, and key rock mechanical parameters (cohesion, elastic modulus, internal friction angle, and Poisson’s ratio) on the post-excavation stress redistribution, displacement field, and fracture evolution in the surrounding rock at engineering scale were analyzed. The results demonstrate that stress concentrations under bias loading conditions primarily located at the arch foot on the deep buried side, the arch crown, and the shoulder region of the shallow side. An increase in bedding spacing effectively inhibits fracture propagation. The bias effect is particularly pronounced at a 45° bedding dip angle relative to 0° and 90°, significantly intensifying the stress concentration, displacement development, and fracture propagation. Reduction in cohesion leads to enhanced fracture development, whereas an increase in elastic modulus significantly reduces displacement magnitudes. A decrease in the internal friction angle increases the risk of shear failure, while an increase in Poisson’s ratio effectively suppresses overall displacement, albeit with limited mitigation of stress concentration. The study elucidates the failure mechanisms of surrounding rock under coupled multi-parameter interactions, providing a theoretical basis and numerical support for the design of support systems in bias tunnels.
Liu et al. (2026) studied this question.