Experimental analysis of mechanical behavior of segmental joint for gas pipeline shield tunnel under unfavorable compression-bending loads

Shield tunnels are usually affected by the larger water pressure when crossing a river. In this paper, the mechanical behavior of a shield tunnel ring seam under unfavorable compression-bending loads is analyzed by means of experiments. The segmental joint specimens were made of prototype segments which were adopted in a gas pipeline shield tunnel project with an inner diameter of 4.25 m and a 1:1 prototype test is applied for this experiment as well. In the experiment, the surface strain, the joint opening and the deflection were measured. The relationship between the joint opening and the internal force at the longitudinal seam have been verified by the prototype loading tests. The experimental results clearly show that the deformation of the segmental joint under different water pressure is restrained by the bolt. Under the influence of the bolt constraint, the maximum joint opening width and the maximum joint opening height show a different growth trend with the increase of bending moment. The axial force has an important influence on the joint deformation and an appropriate increase in axial force under high water pressure conditions is conducive to the suppression of joint deformation. When the axial force is large, with the increase of bending moment, steel bars that bears tension stress may change to sustain compression stress. The bolt stress changes obviously with the changes of axial force and bending moment of the joint. Both tension and compression cracks occur during the joint failure, and are easily occurred in weak position such as waterproof grooves, hand holes etc.