Study On Key Segment Position Optimization Of Universal Ring For Shield Tunnel Of Rapid Railway In Soft Stratum

With the rapid development of China’s economy,a large influx of population in national central cities,rapid increase in traffic pressure,and more serious traffic congestion problems,urban rapid rail transit,as a rapidly developing mode of transportation,has strengthened the connection between central cities and satellite cities.Cultural and economic vitality between large regions,rapid rail transit has outstanding advantages such as large passenger traffic,fast speed,small floor space occupation,energy saving and environmental protection,etc.,and has become an inevitable choice to alleviate the traffic pressure of large cities;rapid rail transit will usher in a faster development of.The rapid rail transit construction is an underground project,and the deformation of the foundation has a greater impact on the underground project,especially in soft soil areas.Investigations on the damage of multiple subway lines that have been opened in many cities have found that many subway lines in early operation have suffered from uneven settlements,cracks,collapse and deformation,and floating segments in different degrees,which seriously affected passenger comfort,and even May pose a serious threat to the safe operation of the subway.Based on the research on the shield lining structure of shield tunnels at home and abroad,this paper studies the assembly position of the universal ring segment capping blocks of shield tunnels in soft soil areas;the research is mainly based on the Tianjin Rail Transit Line Z2 project,using finite element software ABAQUS established a shell-spring model to study the mechanical properties of universal ring segments of shield tunnels in soft soil areas of Tianjin in different buried depths and different assembling positions of capping blocks in different soft soils.The results show that:The bending moment of the general structure of the universal segment increases with the increase of the burial depth;at the same burial depth,the bending moment gradually increases as the soft soil changes from hard to weak.The universal ring capping block has the largest structural bending moment when it is at the top and bottom,which is the most unfavorable to the structural safety;secondly,the position of the arch shoulders on both sides;the capping block is above the arch waist on both sides,and the value of the structural bending moment is the smallest when it is below the arch shoulder.It is most favorable for structural safety,followed by the lower position of arch waist on both sides.On this basis,the finite element software ABAQUS is used to establish a three-dimensional solid model to analyze the different capping block assembly points in weak strata under earthquakes.The internal force of the lining structure and the joint bolt internal forces are analyzed.The results show that different capping block assembly points are affected by earthquakes.The bending moment distribution of the universal ring structure still conforms to the general law: the tunnel vault and arch bottom are generally the maximum positive bending moments,and the arch waists on both sides are generally the maximum negative bending moments.The earthquake and the capping block position have almost no effect on the distribution of the bending moments.The position of the capping block has a significant impact on the change of the maximum bending moment value of the pipe ring structure,and has a small impact on the change of the maximum axial force value of the pipe ring structure.The capping block should be selected to avoid assembling the arch bottom position,and the upper side of the arch waist on both sides should be preferred.Finally,the influence of different capping block location choices on the internal force of the pipe ring structure in the interactive stratum is studied.The results show that:(1)The maximum positive bending moment value of the pipe ring lining structure appears at the vault and the arch bottom,and the maximum negative moment value appears at The characteristics of the bending moment distribution on the sides of the pipe ring are less affected by the interactive stratum,and the distribution of the bending moment value still conforms to the general distribution law.The ground motion will affect the change of the bending moment value of the pipe ring lining.The bending moment value of the lining structure will become larger;(2)the upper ring moment value is slightly greater than the lower bending moment value in the upper and lower soft corners of the interactive stratum;for the capping block assembled on the vault,vault bottom,two When the side arch waist,the bending moment value of the pipe ring structure becomes larger,which is not conducive to the safety of the pipe ring structure,and should be avoided as much as possible.