Study On Mechanical Properties Of Segment Lining Structure For Medium And Small Diameter Shield Tunnel

The utility tunnel can be used for intensification of urban municipal pipelines and effectively solve the problem of "road zipper" caused by pipeline transformation and relocation in the process of urban development.In the reconstruction of municipal pipeline in the old city,the shield method will become the main method of the utility tunnel construction,especially the medium and small diameter shield tunnel is the development direction of the urban utility tunnel in the future.However,the aspect ratio of medium and small diameter shield tunnel is usually larger than the traffic tunnel,and the problem of mechanical characteristics is relatively significant.And the existing utility tunnel related technical specifications lack the explanation of the shield method,and the related research is relatively lack.Under the above background,the paper systematically studies the mechanical characteristics of small and medium diameter shield tunnels under the circumstances of the size of buried depth of tunnel,their own outer diameter,the external formation conditions and the loading and unloading of the urban complex environment by the method of similar model test,theoretical analysis and numerical simulation,and puts forward the problems of the urban complex environment under the influence of the urban complex environment.The results of the research are as follows:1、By using the similar model test,the mechanical and failure characteristics of shield tunnel with medium and small diameter under different buried depth of tunnel,scales and external soft and hard stratigraphic conditions are studied in accordance with the influence of different buried depth of tunnel,scales and the external complex formation conditions on the medium and small diameter shield tunnel.The objective laws of structural deformation,internal force,displacement,contact pressure and acoustic emission information are varied under adverse load conditions.2、Based on the similarity model test and theoretical analysis,the structural stiffness of the shield tunnel with medium and small diameter is analyzed.According to the experimental and theoretical analysis results,the reasonable range of the longitudinal stiffness of the shield tunnel with medium and small diameter is determined,and a modified formula for the longitudinal stiffness of small and medium diameter shield isproposed based on the influence of circular seam and joints.3、With the numerical simulation method,in view of the influence of adjacent building construction on medium and small diameter shield tunnels under the complex environment of the city,the influence of the new structure adding and unloading around the existing shield tunnel is simulated.The stress and deformation characteristics of the shield tunnel in the construction process are analyzed.Time effect and space effect of the structure deformation in the construction process is revealed,and the safety evaluation criterion based on the additional deformation of the existing shield tunnel is put forward,and the control measures for additional deformation of existing tunnels are discussed.