Objective To eliminate the impact of assembly errors on the safety stress evaluation of a shield tunnel target ring structure, it is necessary to study a new method for the health and safety monitoring and evaluation of underground structures.

Method A method for the structural safety evaluation of a single ring is proposed, based on construction records, onsite defect inspection results, and numerical analysis results from a specific subway shield tunnel project. First, finite element numerical analysis is used to calculate the convergence deformation of the target ring under design loads. By comparing the initial detection data, the potential assembly errors are calculated. Then using the onsite cross-section convergence deformation detection results, the actual load-induced convergence deformation is calculated, which is subsequently used as a boundary constraint to back-calculate the true stress conditions of each structure in the tunnel section. Finally, the health status of the structure is judged by comparing the material strength standards of each structure. The calculation accuracy is then verified by correlating the actual onsite condition of each structure. After confirming that the calculated results are generally consistent with the actual condition of each structure, the remaining bearing capacity ratio of the target ring is calculated. Thus, a quantitative evaluation of the target ring structural health status is achieved.

Result & Conclusion  The evaluation results show a high degree of consistency with the actual on-site structural performance. The proposed evaluation method features a clear procedure and strong operability, reflecting the characteristics of the structural condition effectively, particularly in sections with abnormal records during the assembly period.