Optimization of rock bolt support parameters for TBM tunnels in high in situ stress soft rock based on deformation and stress evolution analysis
Abstract
Large deformation of surrounding rock is a critical challenge during TBM tunnelling in deeply buried high in situ stress soft rock, where delayed deformation and insufficient support stiffness may lead to support failure and machine jamming. However, the quantitative influence of rock bolt support parameters on deformation control under such conditions remains insufficiently clarified. In this study, a three dimensional finite element model was established in ABAQUS based on a deeply buried TBM tunnel in Southwest China to investigate the deformation and stress evolution of surrounding rock during excavation and support installation. The effects of key rock bolt parameters, including bolt length, longitudinal spacing, circumferential spacing, and prestress, were systematically evaluated. The results show that a considerable proportion of the final deformation develops ahead of the tunnel face, and crown settlement is the dominant deformation mode. Increasing the bolt length from 3 m to 9 m reduces crown settlement from 101.31 mm to 95.50 mm, corresponding to a reduction of 5.73%, whereas further increasing the length to 11 m produces only a limited additional reduction. Reducing bolt spacing improves deformation control, and the deformation growth becomes more significant when the longitudinal spacing exceeds 80 cm or the circumferential spacing exceeds 60 cm. Increasing bolt prestress enhances the confinement effect of the surrounding rock, but the additional benefit becomes limited when the prestress exceeds 150 kN. Based on the parametric analysis, a support scheme consisting of 9 m bolts, 80 cm longitudinal spacing, 60 cm circumferential spacing, and 150 kN prestress is recommended for similar high in situ stress soft rock TBM tunnels. The results provide a quantitative reference for rock bolt support design and deformation control in deep buried squeezing ground.