Experimental study on deformational resilience of longitudinal joint in shield tunnel lining

Resilience is a functional attribute of shield tunnels to ensure continued serviceability. From the performance-based perspective, the concept of deformational resilience is proposed and defined as the ability to resist deformation development (robustness) and the ability to recover from pre-existing deformation (recoverability). This work aims to measure the deformational resilience of shield tunnel lining structure, targeting at its most vulnerable part-longitudinal joint. For this purpose, a series of full-scale tests are carried out to perform 1) the failure process to simulate external surcharge loads, 2) the recovery process to simulate the effects of unloading and tunnel bilateral soil grouting, and 3) the cyclic loading process to simulate incremental cycling loading and unloading conditions. The assessment of deformational resilience is based on joint opening from the tests and related structural energy analysis. The test results demonstrate that the capability of tunnel longitudinal joint to resist deformation deteriorates with increasing overload level, and the recovery efficiency of joint opening presents nonlinear degradation with the increase of pre-existing deformation. The deformational resilience of longitudinal joint revealed in this research can facilitate the selection of appropriate timing and optimal design of technical parameters related to recovery measures for over-deformed shield tunnels.