Unreinforced construction techniques: ECC-based unreinforced shield tunnel segment joints for enhancing underground infrastructure resilience

The development of unreinforced construction techniques for shield tunnel segments is crucial for enhancing resilience of underground infrastructure, but research in this field is still lacking. This study addresses this gap by conducting full-scale experiments on ECC-based unreinforced shield segment joints (ECCUS) and comparing their performance with traditional reinforced concrete segment joints (RCS) and ECC reinforced segment joints (ECCRS) under extreme bending loads. The research focuses on material characteristics, segmental deflection, joint behavior, bolt strain, damage propagation, failure modes, joint toughness, and ductility. The results revealed that ECCUS joints had a bearing capacity 2.64 times that of RCS and 1.32 times that of ECCRS in the elastic phase. Their ultimate load capacity surpassed RCS by 27.4% and ECCRS by 24.4%. ECCUS also demonstrated superior ductility, with increases of 131% over ECCRS and 78% over RCS, and exhibited finer, more numerous cracks, enhancing energy absorption and deformability. ECCUS bolts showed a 24% reduction in average strain and a 74% decrease in strain deviation compared to RCS and ECCRS. Furthermore, ECCUS joints displayed exceptional toughness, being 6.2 times greater than RCS and 1.5 times higher than ECCRS during normal serviceability. These findings underscore the potential of ECC in improving the performance and durability of unreinforced tunnel segments.