Damage evolution and failure behavior of circumferential joint in large-diameter shield tunnels under compressive-shear loading

Investigating the mechanical and failure behavior of circumferential joints is crucial for optimizing the design and evaluating the serviceability of segmental linings. This study conducted full-scale tests on circumferential joints constructed with tongues and grooves and inclined bolts under positive and negative shear force. The damage evolution and failure characteristics of joint specimens was monitored using an acoustic emission (AE) system, and the analysis focused on joint dislocation, various AE statistical parameters (including hits, energy, RA-AF value, b-value), intensity signal, and spatiotemporal variation of AE events. The results indicate that the variation of joint dislocation and damage follows three stages in both positive and negative shear tests, characterized by joint sliding and tongue and groove contact. The failure mode observed is compression-shear failure due to shear cracks. Significantly larger crack propagation and energy release were noted in negative shear test compared to positive shear test. The contact between tongue and groove can serve as a critical indicator for safety assessment of circumferential joints. The failure characteristics of the joint specimen in positive shear test involves concrete falling off at the groove, while in negative shear tests, damage includes concrete falling off at the groove and bolt hole.