Investigation on structural performance of segmental linings of shield tunnels under loading–unloading-reloading condition

Abstract

The shield tunnel structure built in urban area may suffer from complex disturbance caused by adjacent construction, which leads to loading–unloading-reloading on the tunnel structure, causing accumulation of structural deformation and diseases. In this paper, an elaborate FEM numerical model of segmental linings was established for studying the structural performance of the linings under a loading–unloading-reloading condition which is simulating the complex urban disturbance. The results show that three different deformation modes (Full recovery, Partial recovery and Deformation growth combined with elastic recovery) for the segmental linings can be observed in the unloading process with different historic peak value of the load. A deformation growth phenomenon occurs at the beginning of unloading process in the combined recovery mode and the deformation increment is mainly derived from the change in geometric contact state of joint section. The increase of the load value in loading stage results in the enhancement of nonlinear characteristics and the deterioration of ultimate capacity for the longitudinal joints which directly weaken the deformation recoverability and ultimate capacity of the segmental linings. When the vertical deformation is greater than 50 mm, the deformation recovery rate α_re declines to 0 % and the deformation decrease in elastic recovery stage is covered by the increase in deformation growth stage during unloading process. An index named deformation residual energy E_res was proposed to evaluate the structural safety of the segmental ring. Its decrease can quantitatively reflect the accumulation of unrecoverable deformation and material damage caused by the disturbance conditions.