Study on load distribution characteristics of secondary lining of shield under different construction time

With the massive construction of underwater shield tunnels, the single segmental lining is unable to meet long-term safety requirements in many cases; thus, the double-lining shield tunnel has attracted increasing attention in recent years. The construction time of the secondary lining is a key factor for the mechanical properties of a double lining. In this paper, taking the Shiziyang shield tunnel as the example, we investigate the interaction between shield segment and secondary lining under different construction times by similar model tests. According to the load variation characteristics of the segment and secondary lining structures under different construction times, the load distribution law of a secondary lining structure under the condition of different external loads is analyzed in detail. The results show that (a) the ability of the double-lining structure to bear the external load as a whole will not be changed by a different construction time of the secondary lining, although the bearing capacity at different locations is influenced. (b) Due to the nonuniformly distribution of the stiffness of each part of the segment, the segment and secondary lining have a noncoordinated deformation under the external load. The distribution pattern of the earth pressure outside the segment gradually changes from a uniform distribution to a nonuniform distribution with the delay of the construction time of the secondary lining. In the meantime, the distribution of contact pressure of the joint surface tends to gradually transform from an irregular distribution to a symmetrical distribution along the circumferential direction. (c) The bearing performance of the secondary lining is more stable with the delay of the construction time of the secondary lining during construction, which is more beneficial to the bearing performance of the double-lining structure. In the actual project, it is recommended that the secondary lining be applied when the external loads of the segments are up to 83-100% of the design load, which is beneficial to the bearing performance of the secondary lining.