Study on mechanical and damage characteristics of segment lining under the squeezing action of shield shell

• Design the multi-sensors field tests for large-diameter shield tunnel. • Establish a refined 3D numerical calculation model with the multi-source load. • Analyze the segment dislocation distribution under squeezing action from the shield shell. • Reveal the evolution mechanism of segment damage under shield shell deflection. The shield tail is the final part of the shield shell, and each segment assembled in the shield machine will leave from the shield shell by detaching from shield tail. There are three spatial relationships between the shield shell and the segments: completely at the shield shell, detaching from the shield tail, and completely detached from the shield tail. The squeezing action of the shield shell deflection often leads to the floating and dislocation of the segments and even damage cracking. Based on a refined 3D numerical calculation model considering the multi-source load coupling action and the multi-sensors field tests, this study reveals the mechanical and deformation characteristics as well as the damage evolution mechanism of segments under the deflection squeezing of the shield shell. The research results indicate that the adjacent dislocation of the segments mainly occurs during the segment detaching from the shield tail, and the internal dislocation in the first segment after the shield tail is the largest. The increase in the deflection angle of the shield shell will lead to a more significant increase in the overall vertical compression deformation of the segment. Resulting in the maximum increase in internal dislocation and bolt stress on the upper side of the first segment behind the shield tail. In addition, the adjacent and inter dislocation caused by shield shell deflection is the main cause of segment damage and cracking. The segment damage is mainly tensile damage at the positions of the two sides and upper circumferential joints. The increase in the deflection angle has the greatest impact on the overall tensile damage of the segment that is detaching from the shield tail. Controlling the vertical displacement of the rear end of the shield shell within 50 mm can reduce the floating displacement of the segment by about 67 %. The segment assembly flatness will be significantly improved.