| In order to adapt to the rapid growth of urban population,Chongqing has planned a large scale subway network,and shield tunneling has been widely used in subway construction.Due to the planning needs and the restriction of terrain conditions,the large longitudinal slope or small radius curve tunnel is inevitable in some sections,which brings difficulties for shield tunneling and segment assembly,and the stress characteristics of segment segment are also to be studied.In this paper,based on the section of Chongqing rail transit line segment,the stress characteristics of segment in small radius,large longitudinal slope section,the bending performance of segment joint,the shield propulsion axis control and segment assembly technology,the main research content and innovation results are as follows:1.Force analysis of segment segment of small radius curve segment(1)the curve radius of segment erector is not simple linear change,with the decrease of curve radius,the bending moment,axial force,shear force and segment length increase significantly.(2)under the condition of small curve radius,there will be tensile stress in the segment outer ring(curve side),which shows that the outside part of segment is relatively weak and should be strengthened in the curve segment.(3)with the decrease of curve radius,the tension of segment joint increases gradually.When the curve radius is 50 m,the inner surface of the segment is 1.04 mm,and the segment withstands the outer arc surface to reach 1.59 mm,and the waterproof ability is greatly reduced.2.Analysis of formation disturbance and excavation surface stability of large longitudinal slope section(1)under different grades conditions,the deformation law of soil x,z direction is roughly similar,but the soil x displacement is small,z direction(vertical)displacement,especially the maximum displacement of the center of the tunnel,and increase with the tunnel.(2)the stress of the excavation slope decreases with the increase of the slope gradient,and the more easy to lose the instability,the supporting force of the excavationsurface should be jiadui during shield construction;The compressive stress of excavation surface increases with the increase of depth,the higher the stability of excavation surface.Compared with the change of value of slope,the effect of buried depth on the stress size of excavation surface is much more obvious.3.Analysis on the acceptance characteristics of segment jointThe change of joint bending stiffness is actually the coupling result of many factors,and is affected by the load and joint structure.In contrast,the bending stiffness is more obvious affected by axial force,bending moment and bolt height.The increase of bending moment reduces the bending stiffness,the increase of axial force increases bending stiffness,and the influence of bolt height is mainly reflected in the change of the positive and negative bending moment of the joint.4.Quality control of segment erector of small radius shield tunnelIn the small radius section,the axis deviation of segment is reduced by reasonably controlling the chaowaliang and splice angle of the profiling tool.In order to prevent the large deformation of the segment,it is advisable to use the early strength of the grouting material with high strength,and to set the Prepared offset reasonably;In order to prevent the upward buoyancy caused by the longitudinal dislocation of the segment,it is advisable to use the early strength of high grouting material,and increase the preload of longitudinal bolt appropriately. |
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