Study on the mechanical performance of large-diameter shield tunnel segments with DDCI connectors

During the shield tunnel design, the joints of the lining segments are given special attention due to the relatively low strength and the risk of leakage. The stability and durability of the whole tunnel structure will significantly decrease once the joints fail, especially for large-diameter tunnels. In this paper, a new connector composed of major-D part, minor-D part, C part, I part and anchor bars (called DDCI connector) was proposed. Consequently, numerical simulations were conducted to optimize the design of the DDCI connector. Finally, the full-scale axial tensile and shear tests were carried out to investigate the mechanical response and failure process of large-diameter shield tunnel segments with DDCI connectors. The results show that the stiffness of the DDCI connector could be effectively enhanced by adopting the wedge-type I part, reducing the length of the cantilever end of the minor-D part, and increasing the thickness of the C and D parts. Moreover, the variation trends of joint opening, anchor bar stress, and joint dislocation in full-scale tests all exhibit a three-stage characteristic. Similarly, the failure process of both specimens can be summarized into the self-coordination stage, the cooperative bearing stage, and the cracking failure stage. After reaching the ultimate load, distinct crack propagation behavior is found, which can be divided into four steps according to the observed distribution characteristics. The results can provide guidance and data support for further improving the application of DDCI connectors in large-diameter shield tunnels.