A Novel Back-Analysis Approach for the External Loads on Shield Tunnel Lining in Service Based on Monitored Deformation

The maintenance of in-service shield tunnel lining has become a critical issue in recent decades due to the rapid development of the metro system in China. The external load is one of the most important factors influencing the deformation and performance of the in-service shield tunnels. It is hard to evaluate the external load since it is influenced by complex factors. And the arbitrary-distributed external load is not considered in the existing theories. A novel back-analysis approach for evaluating the external load using the deformation of tunnel lining was proposed based on Betti’s theorem. The theoretical rationality of the proposed method is analyzed, and the workflow is provided. The data and simulation models for a model test were adopted to validate the effectiveness and accuracy of the proposed method. The results show that the external loads can be back-analyzed with satisfying accuracy and low computational cost. Then, the practical application was conducted for an in-service shield tunnel. In addition, the workflow combined with laser scanning and back analysis was proposed for evaluating the practical loads. The proposed approach can be used for the back analysis of the external loads based on lining deformation scanned inside tunnels, with good performance.