Experiments And Analyses Of Strengthened Longitudinal Joints Of Shield Tunnel Lining

Segmental joints are generally the weakest part of shield tunnel lining structure, and appear to play a critical role in overall structural performance. Nevertheless, little attention is paid to such joints. Our preliminary study slightly explored the feasibility of strengthening longitudinal joints with channel steel members under positive bending moment. Based on that, the present study veers to the effectiveness of that strengthening strategy to strengthen such joints under negative bending moment or after fire. The main works are as follows:1. To investigate the mechanical behaviors under negative bending moment as well as comparatively analyze the strengthening effects, three longitudinal joints that were previously strengthened by steel plates and channel steels with the same amount of steel were tested. It is showed that:(1) after strengthening, an increase of the effective load bearing capacity 85 % and 121% is obtained for steel plates strengthened specimen and channel steels strengthened specimen, respectively, and the joint opening of the former is significantly less than the latter comparing to the control specimen;(2) a distinguishing feature of double-line is showed by the vertical load-joint deflection curves of strengthened specimens. Though the initial stiffness of both are basically identical, the latter exhibits superior deformation resistance behavior than the former; 3) the strengthening effect can be further achieved through the enhancement of anchorage at a certain range(±250 mm at longitudinal seam), a place where the strains of reinforcement mainly concentrated.2. A three dimensional model of longitudinal joint was established by using finite element software ABAQUS. In case of the same amount of steel, the mechanical behaviors of strengthened joints under positive and negative bending moment with different types and quantities of channel steel member were analyzed using that model. The results reveal that: to lower the effect of reinforcement members on tunnel clearance, appropriately reducing section height of channel steel and increasing its length or quantities can hardly affect initial stiffness, but in another way strengthen both load-bearing capacity and late stiffness of joints under positive bending moment. However, this tactic doesn’t work for the joint negative load-bearing capacity3. To investigate residual mechanical behaviors and strengthening effect of fire-damaged joints, fire tests and post-fire mechanical behavior tests of five specimens under positive bending moment, including unreinforced/ reinforced longitudinal joints, were conducted. It is observed that:(1) the segmental concrete spalling is expected to occur primarily at the central of intrados instead of near the joints. It takes place after heating up 10 minutes, and lasts for 12~22 minutes. The depth of the maximum explosive spalling is about the thickness of the protective layer;(2) within a duration of 120 min in the fire, the temperature of the rubber gasket is about 60~90℃, guidance rod 100~120℃, bolt at segmental joint 550~600℃;(3) owing to the use of the channel steel member as reinforcements, the load bearing capacity of fire-damaged specimens is effectively enhanced compared to that without strengthening. It is even higher than the one at ambient temperature. Apart from that, the stiffness is positively improved.