Creep characteristics of muddy siltstone and its engineering application on cross-river tunnel stability.

Muddy siltstone combines the characteristics of both sandstone and mudstone, and is prone to instability over time. To study the long-term stability of tunnel engineering in this stratum, this article taking the cross-river metro tunnel section as the engineering background, and conducting research on the stress and deformation of the tunnel surrounding rock. Firstly, uniaxial compression creep tests were conducted on muddy siltstone to study the creep deformation law under graded loading. Secondly, a nonlinear damage creep model was established based on the Burgers model, and the experimental results were fitted. Finally, the proposed creep model was applied to the COMSOL Multiphysics numerical simulation software to perform multi field coupled calculations on the operation of metro tunnels. The research results show that: (1) Muddy siltstone undergoes the entire process of decaying creep, steady creep and accelerated creep. (2) The proposed nonlinear damage creep model can accurately describe the creep characteristics of muddy siltstone, especially in the accelerated creep stage. (3) Applying nonlinear damage creep model to tunnel numerical simulation calculation, it was found that the most obvious part of tunnel rock creep deformation is the tunnel arch crown. By comparing with on-site monitoring data, indicated that the established creep-fluid-structure coupling tunnel model can be used to predict surrounding rock deformation. The creep-fluid-structure coupling tunnel model proposed in this study provides a new perspective for the design and safety assessment of cross river tunnels in soft rock formations, which helps to achieve more accurate long-term stability prediction.