Investigation of mechanical failure performance of a large-diameter shield tunnel segmental ring

The control criteria for structural deformation and the evaluation of operational safety performance for large-diameter shield tunnel segments are not yet clearly defined. To address this issue, a refined 3D finite element model was established to analyze the transverse deformation response of a large-diameter segmental ring. By analyzing the stress, deformation, and crack distribution of large-diameter segments under overload conditions, the transverse deformation of the segmental ring could be divided into four stages. The main reasons for the decrease in segmental ring stiffness were found to be the extensive development of cracks and the complete formation of four plastic hinges. The deformation control value for the large-diameter shield tunnel segment is chosen as 8 parts per thousand of the segment's outer diameter, representing the transverse deformation during the formation of the first semi-plastic hinge (i.e., the first yield point) in the structure. This control value can serve as a reinforcement standard for preventing the failure of large-diameter shield tunnel segments. The flexural bearing capacity characteristic curve of segments was used to evaluate the structural strength of a large-diameter segmental ring. It was discovered that the maximum internal force combination of the segment did not exceed the segment ultimate bearing capacity curve (SUBC). However, the combination of internal force at 9(degrees), 85(degrees), and 161(degrees) of the joints, and their symmetrical locations about the 0(degrees)-180(degrees) axis exceeded the joint ultimate bearing capacity curve (JUBC). The results indicate that the failure of the large-diameter segment lining was mainly due to insufficient joint strength, leading to an instability failure. The findings from this study can be used to develop more effective maintenance strategies for large-diameter shield tunnel segments to ensure their long-term performance.