Study On The Deformation Influence To Existing Pipeline Caused By Undercrossing Shield Tunnel

With the accelerating process of urbanization in China,the scale of major cities continues to expand,making the rapid development of underground space engineering.There are more and more new shield tunnels undercrossing the existing pipeline projects.To ensure the safe of the existing pipeline and the new tunnel is the basic requirement of the tunnel crossing project.During the tunnel construction,the surrounding soil will be deformed,which will lead to the deformation and internal force of the existing pipeline,threatening the safe operation and service life of the pipeline.It is of great significance to analyze the deformation and stress state of the existing pipeline during the new tunnel excavation.In this paper,theoretical analysis,numerical simulation and model test were used to study the deformation mechanism of existing pipelines under the influence of tunnelling.The main work and research results are as follows.(1)Based on the two-stage analysis method,considering the shear effect of pipeline caused by uneven settlement,the deformation and internal force of existing pipeline caused by tunnel excavation were studied,and a variety of influencing factors were analyzed.The maximum longitudinal settlement of the existing pipeline is located above the central axis of the new tunnel.The pipeline settlement curve conforms to the Gaussian distribution characteristics,and the settlement gradually decreases from the center to both sides.The maximum shear force of the pipeline is mainly located at the edge of the outer diameter of the tunnel.The maximum bending moment occurs in the center of the new tunnel which is the same as the maximum deformation position of the pipeline,which is the most dangerous section of the existing pipeline.(2)Three-dimensional finite element models were established to simulate the dynamic changes of the existing pipeline and ground deformation during the tunnel excavation,and the results were compared with the theoretical calculation results.The results show that the deformation curves of pipeline and ground surface conform to Gaussian distribution,and the maximum value is above the axis of the new tunnel.When the tunnel excavation face passes directly under the pipeline,the deformation value of pipeline and ground surface will increase greatly.At a distance of ±20m from the center line of the tunnel,a certain amount of uplift will occur between the pipeline and the ground surface.The main influence area of the new tunnel excavation on the deformation of the existing pipeline is within the outer diameter of the tunnel.(3)Based on PIV and transparent soil,the deformation of existing pipelines and ground surface during tunnel underpass construction was studied.It is found that the deformation curves of pipeline and surface conform to the characteristics of Gauss curve.The closer the shield excavation face is to the center line of the pipeline,the greater the deformation of the pipeline and the surface.The influence of tunnel excavation on the pipeline is about 4 times of tunnel diameter,and there is a certain amount of uplift at both ends of the pipeline and the surface.The existence of pipelines has a shielding effect on the deformation of the surface above.(4)In the parameter analysis,the net distance between the tunnel and the pipe and the tunnel diameter have a greater impact on the deformation of the existing pipeline.Poisson’s ratio of soil,the elastic modulus of pipeline,the buried depth of pipeline and the ground loss rate have a smaller impact on the deformation of the pipeline.This thesis has 88 figures,5 tables and 147 references.