In response to extensive cracking and fracture in the segment lining of an underlying shield tunnel subjected to large-scale ground unloading, this paper adopts a real-world shield tunnel project as a case study. The underlying shield tunnel is experiencing overall heaving deformation, characterized by a decrease in its horizontal diameter. The longitudinal joint at the tunnel vault transitions from opening to crushing at the intrados. This paper presents the stress behavior in the tunnel vault, which is characterized by negligible fluctuations in axial force concurrent with a pronounced decrease in bending moment. This indicates that the ground unloading and the increase of tunnel’s vertical diameter constitute the primary causes of the intrados crushing at longitudinal joint of tunnel vault. And the intrados crushing, in conjunction with segment misalignment observed on-site, results in a transition in the interface behavior to a line-to-surface contact. Consequently, the lining stress near the intrados exceeds permissible limits, thereby resulting in subsequent cracking and fracture. The primary threats to the structural safety of segment lining arise from the increased vertical ovalization, the intrados crushing and uneven line-to-surface contact at longitudinal joint of tunnel vault, rather than from the changes in lining stress.
Dai et al. (Thu,) studied this question.