The deformation and failure characteristics of tunnels in layered rock with gentle dip angles after freeze–thaw cycles: Physical model tests and numerical investigation

When a tunnel passes through layered rock with a gentle dip angle in cold regions, the occurrence of multiple freeze–thaw (F–T) cycles can easily cause fatigue damage to the rock bedding surfaces and seriously affect the rock stability. One of the engineering problems that needs to be solved is to determine the deformation and failure mechanisms of such surrounding rock under F–T cycles. Based on the similarity principle, the mechanical response of the tunnel lining structure and the progressive failure process of the surrounding rock under long-term F–T action were studied by performing physical model tests and numerical simulations. The results show that the model tunnel lining partially separates from the surrounding layered rock with a gentle dip angle under the action of F–T cycles. Moreover, the load bearing capacity of the model weakens after undergoing F–T cycles. Additionally, the bending moment and axial force evolution characteristics of the tunnel and surrounding rock model are consistent with the deformation characteristics, which agree with the actual mechanical and deformation characteristics of a real tunnel under F–T cycles. After establishing numerical calculation models for surrounding rock with three bedding angles (0°, 10°, and 20°) and verifying the numerical models based on the test results, the horizontal and vertical displacements of the surrounding rock in the tunnel entrance section under ground stress conditions at a depth of 400 m were calculated. The research results accurately reflect the long-term deformation characteristics of layered rock with gentle dip angles surrounding tunnels in cold regions and can provide theoretical guidance for the application of corresponding tunnel support measures in cold regions.