Study on the damage evolution of secondary tunnel lining in layered rock stratum

Concrete cracking is prone to occur in secondary linings during tunnel operation. In this article, the Zhegu mountain tunnel, which is mainly situated in weak phyllite stratum, was taken as an example to study this issue. Firstly, a field investigation was conducted to reveal the cracking status of the tunnel lining. Then, similarity model tests were adopted to analyze the mechanical responses of linings in layered rock strata with different inclination angles. Finally, the damage Mohr-Coulomb criterion with a statistical distribution feature is put forward to investigate the damage patterns of linings. The results show that: (1) the anisotropic behavior of phyllite is the main factor that causes the asymmetric cracking in secondary lining. (2) The distribution of inner force and displacement along tunnel perimeter has distinct asymmetric features, and their increasing trends with loading steps contain three stages, e.g., elastically, plastically, and unsteadily deformed stage. (3) The failure processes of linings situated in layered strata with different inclination angles are similar with three pronounced period, that is, initial damage period, damage period, and instability period.(4) For layered stratum, the serious damage sections of lining are distributed in certain range with the tangent of tunnel contour being parallel to the direction of bedding planes, and the line connecting the central points of serious damage sections on both sides deflects toward the direction of minor principal stress to a certain extent.(5) The existence of void leads to a more concentrated distribution of serious damage area in lining than that of lining with no void behind it.