Abstract:  The repair and governance of shield tunnels are widely common nowadays. Hence, it is essential to improve the reinforcement system of the tunnel segments. In this study, the deficiencies in the existing Usteel reinforcement are presented, and a finite element study of the crosssection of Usteel reinforced shield tunnel segment is conducted. The MIDAS GTS NX finite element software is employed to establish a fine threedimensional segment model, and the simulation results are compared with the fullscale test results. In addition, the influencing factors, such as the number of Usteel rings, assembly form, and reinforcement form, are examined to investigate the mechanical deformation performance and reinforcement effect of Usteel reinforced segments under excavation unloading of the side foundation pit. The research results reveal the following: (1) The fourring Usteel reinforcement minimizes the convergence deformation of segments and reduces the principal stress of bolts. (2) The topbottom convergence deformation and bolt stress of the segment under the staggered seam assembly form are smaller than those of the throughseam assembly before and after Usteel reinforcement. (3) The maximum principal stress of Usteel is mainly located at the top, waist, and 200°~220° transition section and it can be strengthened locally. (4) The combination reinforcement of Usteel and steel plate is found to be a reliable reinforcement method that has significant reinforcement effect on the convergence deformation of the top and bottom of the segment. The maximum reinforcement efficiency can reach 45.8% with a good economic benefit.

Key words: shield segment, finite element simulation, Usteel reinforcement, unloading condition, reinforcement effect