Research On Stability Of Segmental Lining Structure Of Shield Tunnel

With a large number of city metro shield tunnel and underwater railway or highway shield tunnel with large cross-section being built, the problems of long-term security and stability of shield tunnel are coming. At present, the design theory of shield tunnel lining structure is calculated from the aspects of the strength of concrete, the cracking of concrete, the joint strength and the joint opening amount. The stability of the whole segmental lining structure of shield tunnel is lack of consideration. In practical engineering, weak resistance strata, degradation of material properties of segment lining, human activities affect such as the construction of near buildings, the extraction of groundwater and other factors will have a negative impact on the stability of shield tunnel. But there is no relevant theoretical criterion, and related research is currently very little.This thesis is supported by National Basic Research Program of China (973 Program): ’Long-term safety and prediction method of underground structures under complex environments’and the National Natural Science Foundation:’study on mechanical behaviors of segment joint for shield tunnel with large cross-sections’. Theoretical analysis, model test and numerical analysis means are mainly adopted to analyze the stability of the segment lining of shield tunnel. The aims is to reveal the instability behaviors of segment lining of shield tunnel and prove the instability criterion of the segment lining of shield tunnel. The main works and research achievements are as follows:1、Basted on the typical shield tunnel in our country at present, including the city subway shield tunnel with about 6m outer diameters, underwater highway or railway shield tunnel with about 10m outer diameters, and underwater highway or railway shield tunnel with about 15m outer diameters, the bending behaviors of the segment joint are analyzed using the numerical simulation method. The value range of the bending stiffness of the segment joint for the typical shield tunnel is given.2、Taking Shiziyang underwater railway shield tunnel with 10.8m outer diameter as the research object, the influence law of the bending stiffness of segment joint on the internal force and deformation of segment lining are analyzed by means of numerical analysis. Using the shell-spring calculation model based on the nonlinear relationship of joint bending stiffness-moment-axial force, the joint bending stiffness consisting with the internal force of segment lining structure is proved. The working state of segment joint is more accurate, and this is helpful to optimize the design.3、By means of the stability analysis method of nonlinear finite element, the instability mechanical characteristics of segment lining under the different formation condition, joint stiffness and assembling mode are analysed. The influence degree and law of the different factors on the stability of shield tunnel structure is investigated.4、Using "shield tunnel-ground complex simulation facility", the similarity model test of the stability of segment lining structure of shield tunnel are carried out for the soft clay strata conditions which standard penetration degree is less than 5. The influence law of the joint bending stiffness, assembling mode, segment stiffness, and strata cavity on the stability of the segment structure are studied. The instability behaviors of segment lining structure are proved. Combined with the numerical analysis results, the suggestions of instability failure judge for the shield tunnel segment structure are presented.5、Adopting the stability analysis method of nonlinear finite element, the stability of segment lining structure of shield tunnel under special conditions is studied, including the partly weaken strata resistance, complex strata condition, the change of underground water level, and the structure performance degradation due to long-term underground environment. The instability mechanism and instability behaviors of segment lining structure under different conditions are revealed.