Mechanical performance and failure-mitigation mechanism of a steel–rubber–aluminium-alloy-bar functional lining segment for fault-crossing shield tunnels

Fault dislocation can subject tunnel linings to compression–shear coupling arising from spatially incompatible deformation, leading to local stress concentration, stiffness degradation and functional failure. For conventional reinforced-concrete linings, the critical issue is not only insufficient strength, but also the limited ability to accommodate imposed ground displacement without damage localization. To mitigate this failure tendency, this study proposes steel–rubber–aluminium-alloy-bar functional lining segments, hereafter referred to as SRB functional lining segments, for fault-crossing shield tunnels. The SRB functional segment is designed to transform fault-induced incompatible deformation into constrained shear deformation and hysteretic energy dissipation while maintaining load-transfer continuity. Six scaled SRB specimens were tested under constant axial compression and cyclic horizontal displacement, which was adopted as a simplified component-level representation of fault-induced compression–shear deformation. The hysteretic response, equivalent horizontal stiffness and equivalent damping ratio were evaluated to quantify deformation accommodation, lateral stiffness retention and hysteretic energy-dissipation capacity. A three-dimensional finite element model was established and validated against the test results, and a simplified reinforced-concrete reference segment was introduced to assess the relative stress redistribution and performance-retention tendency under the same displacement-input framework. Under the adopted three-cycle loading protocol, the SRB functional lining ring exhibited an approximately symmetric hysteretic response without an abrupt reduction in resistance over the investigated displacement range. The equivalent horizontal stiffness ranged from 0.275 to 0.404 kN/mm, and the equivalent damping ratio ranged from 10.71% to 14.04%. Compared with the simplified reinforced-concrete reference lining ring, the SRB functional segment showed a more distributed stress pattern and a lower peak equivalent stress in the vulnerable region, with the peak Mises stress reduced from 22.53 MPa to 9.096 MPa under the adopted component-level loading condition. The normalized stiffness- and damping-response comparisons further showed higher response-retention indices for the SRB functional lining ring than for the reinforced-concrete reference lining ring under increasing displacement demand. These findings provide component-level experimental and numerical evidence that the SRB functional lining ring can potentially mitigate local failure tendency by converting fault-induced deformation incompatibility into constrained shear deformation while maintaining load-transfer continuity.