Abstract: Conventional shield tunnel strengthening faces various limitations, such as time-consuming construction and low efficiency. Therefore, in this study, a novel segment strengthening technique is proposed to address these limitations and achieve rapid repair. This technique utilizes engineered cementitious composite (ECC) as a prefabricated, non-removable formwork, with C60 concrete grouting forming the reinforcement core. Full-scale tests are conducted to investigate the mechanical performance of the strengthened structure, leading to the following conclusions: (1) The failure mode of the reinforced structure can be divided into three stages: the elastic, damage development, and ultimate failure stages. In the elastic stage, the original structure, reinforcement body, and bonding interface proportionally share the load. As damage is initiated, the internal forces among the structural parts undergo considerable adjustment, marking the transition into the damage development stage. Complete failure of any component leads to a dramatic degradation of the structural stiffness, entering the ultimate failure stage. (2) Reinforced segments exhibit higher ultimate bearing capacity and stiffness compared to reinforced joints, even though the ultimate deformation of the structure is smaller. Under a negative bending moment, the stiffness of the reinforced structure is higher than under a positive bending moment. The ultimate joint capacity remains similar for positive and negative bending moments, whereas the ultimate bearing capacity of segments under a positive bending moment is lower than under a negative bending moment. (3) ECC offers several advantages over conventional concrete, such as high strength and low density, making it an excellent material for prefabricated, non-removable formworks due to its excellent overall performance. During reinforcement construction, intensified surface roughening and enhanced post-installed anchoring are recommended for the crown and joints of the tunnel structure to improve interfacial bonding strength.

Key words: shield tunnel, engineered cementitious composite, flexural performance, structural reinforcement, full-scale test