Experimental study on effect of ductile-iron panel stiffness on mechanical properties of segmental joints of shield tunnels

In circular shield tunnels bearing high inner pressure or rectangular shaped shield tunnels, as the axial force at the segmental lining decreases, the bolt load at the segmental joint increases. It is essential to adopt high-stiffness segmental joints to improve the bearing capacity and control the deformation at the joint position. When designing high-stiffness segmental joints, the selection of ductileiron joint panel is crucial. In this study, two types of segmental joints with different joint panels were fabricated, and the effects of joint panel stiffness on the mechanical properties of segmental joints were analyzed through full-scale sagging and hogging bending tests. The results showed that the failure mode of high-stiffness segmental joint was similar to that of large eccentric compression section. According to the difference of panel stiffness, the failure modes can be specified into two types. If the stiffness is sufficient, the joint failure occurs due to the yielding of bolts; otherwise, it occurs due to the large deformation of ductile-iron joint panels. As for the design requirement of segmental joint, the stiffness of joint panel should be sufficient, i.e., the opening and failure of the joints are finally induced by the bolt deformation. Otherwise, before the plastic deformation of the bolts, the large deformation of the joint panels will occur under a bendingmoment-dominant load, and the bearing capacity of the joints will greatly decrease.