Full-scale test and numerical simulation of three-ring staggered-joint shield segment reinforcement under ultimate load conditions

Using the self-developed multiring shield segment prototype test loading system, the three-ring staggered full-scale segments under ultimate loading are tested to investigate the mechanical characteristics of the segments before and after reinforcement. Then, a numerical simulation is carried out based on the MIDAS GTS NX to study the stiffness change before and after segment reinforcement. The test results show that the maximum bending moment at the waist of the reinforced segment moves down, and the maximum offset and bolt stress are greatly reduced. The maximum offset occurs at the waist and top of the reinforced segment, and joint 5 bears the maximum shear stress and principal stress, which decreased by 29.5% and 28.6%, respectively. Compared with the single-ring shield segment after reinforcement, the three-ring segment enters the plastic state earlier, and the overall stiffness of the segment is greatly improved, which can weaken the intermediate stage of plastic deformation and delay the process of the segment entering the plastic state. In addition, the stiffness of the unreinforced segment decreases sharply when its lateral convergence deformation is greater than 25.03 mm, but the stiffness of the reinforced segment is still in a stable state. The plastic deformation of the concrete starts from the bolt hole and goes along the bolt hole to the two ends of the bolt. Lateral expansion occurred, and the bolts of the reinforced segment did not break during the whole loading process.