Sealant performance and leakage mechanisms in shield tunnels with T-joint effects: A pathfinding-based approach integrating contact stress analysis

T-joints represent a critical yet distinct structural feature in shield tunnels, exhibiting fundamentally different sealant performance and leakage behaviours compared to continuous joints. This study presents a novel pathfinding algorithm-based approach integrating contact stress analysis to evaluate localised sealant behaviour and leakage mechanisms affected by T-joints under various deformation patterns. The approach enables simultaneous assessment of waterproof capacity and identification of potential leakage paths. The effectiveness of the proposed approach is validated by comparing with laboratory testing data. It is further demonstrated that the waterproof capacity of T-joints can be effectively characterised by an ellipsoid function accounting for joint offset and openings in both circumferential and longitudinal directions. Joint offset substantially reduces waterproof capacity and creates localised lift-up areas with critically low contact stress due to gasket-to-groove interaction. Longitudinal joint openings exhibit less impact on waterproofing performance compared to circumferential openings, with residual sealing capacity maintained even at full opening displacement. A newly proposed leakage centralisation ratio reveals four distinct leakage regions, whose formation depends on joint-specific contact behaviour governed by opening and offset parameters. These insights provide a quantitative basis for optimising T-joint design in shield tunnels, with particular relevance for waterproofing system performance under complex loading conditions.