Test Study On Mechanical Properties Of Presstressed Shield Tunnel Segment Joint

Shield tunnel, due to its unique advantages, has been applied in more and morewider fields. At present, there appear many new forms of shield tunnel segmentstructure. The prestressed shield tunnel segment structure is one of them. On one hand,the prestressed technology can overcome the problems caused by defects of concrete(such as being very heavy and prone to cracking or damage). On the other hand, it canbe used as a method of assembly to strengthen the ring stiffness of segment structure,to accelerate the assembly efficiency of segments and improve economic benefit, sothe prestressed shield tunnel technology has a wide application prospect in the field ofshield tunnel engineering.This paper focuses on the joint test on large scale for the prestressed shield tunnelsegment. An analysis was made on the mechanical properties（Specific includingJoint bending stiffness， Segment stress distribution near the joint and Jointdeformation）of prestressed shield segment joint in different conditions, which haslaid the theoretical foundation on application and popularization of the prestressedtechnology in the shield tunnel.The test prototype is a subway tunnel with a diameter of about6m. First of all,based on research and analysis on a large number of literature concerning generalshield tunnel segment joint and the prestressed shield tunnel segment joints, a detailedtest program was designed. The second，using different joint forms (whether there aretongues and grooves), the effect of positive/negative bending moments as well as theeffect of curved prestressed tendons on bending stiffness of prestressed shield tunnelsegment joints were studied. In addition, joint’s mechanical properties under repeatloading test were analyzed.As far as the data analysis is concerned, a comparison was made on variousconditions and an analysis was also made on the effects of various factors on the mechanical properties of the joints, which focus on the analysis of the joints inbending stiffness, the stress distribution near the joints and outside the arc deflection ofsegments. Based on the above, a comparison was also made on the test results andtheoretical research.Based on the experimental research, the author performed the numericalsimulation. The analysis results were compared with the test results, and then ananalysis was made on the effects of different prestressed tonnage on mechanicalproperties of the shield tunnel segment joints.The research indicates that, the tongue-and-groove joint has relatively highshear-bearing capacity, but its Joint bending stiffness is relatively low; using curvedprestressed tendons has higher joint bending stiffness than using rectilinear ones; thejoint bearing negative moment easily leads to the decreasing of the bearing capacity ofthe structure, or it may lead to the structural failure of the segment due to the stressconcentration; compared with the segment joint of the common shield tunnel, thesegment joint of the pre-stressed shield tunnel has the function of automatic closingand self adjusting, which is so favorable for improving the durability when thestructure bears the dynamic load; the introduction of pre-stressed reinforcementchanges the stress distribution of the segment structure, so that the occurrence of thesegment crack can be postponed, which does good to improve the bearing capacity,durability and water-proof effect of the lining structure.