Model tests on reasonable construction time of secondary lining of shield tunnel

Recently, the double-layer lining of shield tunnels has begun to be applied as a new form. However, due to the lack of the related researches, the key parameters of the double-layer lining structure system of shield tunnels are still unclear. The construction time of the second lining is one of them. Based on the Shiziyang Tunnel Project, a similar model test is used to study the reasonable construction time of the secondary lining. The results show that the secondary lining is only used as the auxiliary bearing structure in the double-layer lining of the shield tunnel. When the construction time is 57%~83%, the radial convergence and ellipticity of the structure change most slowly with the loading step, and the cumulative AE number of the structure increases progressively. If it is constructed too early or too late, the secondary lining can not effectively inhibit the deformation of the segment lining, and the cumulative AE number of the structure increases stepwisely. With the delay of the construction time of the secondary lining, the ratio of the maximum internal strength of the secondary lining to that of the segment lining and the load level of the macroscopic damage at the beginning of the structure both increase first and then decrease. Therefore, considering the deformation history and damage characteristics of the double-layer lining structure during the loading process, the reasonable construction time of the secondary lining is 57%~83%.