Lateral asymptotic deflection evolution and mechanical behavior of secondary linings of freeze-thaw tunnels in cold regions

The seasonal freezing and thawing in cold regions result in the spatial reconstruction of stress and strain in fractured strata and loosening zones of the surrounding rocks. To describe the asymptotic evolution of transverse deflection of tunnel linings under the influences of freezing and thawing, the key characteristics of asymptotic deflection, evolution of rupture layer, loosening zone and stress-strain of linings in the period of positive temperature (PT), negative temperature (NT), frozen season (FS) and melting season (MS) are analyzed based on the 390 days’ in-situ inclination deformation data of the arch waist and wall at tunnel entrance and in the middle section in the Laoyeling cold region of Jilin Province, China. The numerical simulation tests are applied and combined with the mechanical properties of cracking and deflection of linings. The results show that the deflection at tunnel entrance changes significantly with the alternation of seasonal cold. The wall and waist of the left arch are "inverted V"- and "concave"-shaped, respectively. In terms of deflection response, it shows a "lag" in MS and an "ahead" trend in FS, and a "sudden change" trend in MS and FS. And the influence in the middle section of the tunnel is smaller than that at the entrance. The waist of the right arch has different degrees of "fluctuation" deflection in FS and PT, while that of the left arch presents "concave" change, and it has "lag" deflection in MS. The calculated diameter of loosening circle satisfies MS & FS>NT>PT, and that at the entrance is larger than that in the middle of the tunnel. The contour of plastic zone is larger than that of loosening ring by numerical simulation. Therefore, the damage of the linings during the freeze-thaw period is more significant than that in other periods, so the risk of deflection of linings caused by temperature change should be highlighted.