Mechanism And Calculation Method Of Existing Pipe-Soil Uncoordinated Deformation Caused By Shield Tunnelling Underneath

With the rapidly development of urban rail transportation,new tunnels crossing existing pipes are becoming more and more common.New tunnel excavation inevitably causes deformation of existing pipelines,which induces diseases such as segment cracking and water seepage in joints.This is a threat to the operational safety of subway tunnels.Accurate prediction of existing pipe deformation caused by shield tunnelling underneath pipe construction has become a hot topic in current urban rail transit engineering.In this paper,we first establish the numerical model of shield tunnelling underneath pipe construction.The separation mechanism at the bottom of the pipe caused by tunnel excavation is analyzed in depth.Secondly,the existing pipe is regarded as an Euler beam on a tension-free elastic foundation.Based on the contact state between the existing pipeline and the bottom soil,a calculation equation of the existing pipeline displacement caused by shield tunnelling underneath pipe construction is derived.Finally,the effect of vertical soil pressure,bending stiffness,angle between pipe and tunnel,and ground loss ratio is studied using the method of this paper.The main work and results of this paper are as follows:1.ABAQUS finite element software is used to model the tunnel under existing pipelines.The tunnel excavation is simulated by the raw-dead unit method and the ground loss is controlled using the displacement boundary method.Factors such as palm surface pressure and injection pressure are considered,and the mechanism of uncoordinated pipe-soil deformation during tunnel excavation is analyzed.The effects of pipe bending stiffness,burial depth and ground loss ratio on the uncoordinated deformation mechanism are discussed.The results show that when the pipe burial depth is small and the bending stiffness and ground loss ratio are large,the pipe and soil uncoordinated deformation occurs.With the increase of pipe burial depth and bending stiffness and ground loss ratio,the length of separated area beneath the pipe decreases,and then the pipe-soil shows coordinated deformation.2.Combing with the uncoordinated deformation mechanism of the pipe-soil,the pipe is regarded as an Euler-Bernoulli beam on a Winkler foundation.The two-stage analysis method is used to derive the theoretical calculation method of the mechanical response of the pipe,and the reliability of the method in this paper is verified in comparison with existing studies.The effects of bending stiffness of pipe,pipe burial depth,pipe and tunnel angle,and ground loss ratio are discussed.The results show that with the increase of bending stiffness and ground loss ratio,the angle between pipe and tunnel and the burial depth of pipe decrease,leading to the increase of length of separated area beneath pipe and the maximum value of mechanical response Conversely,the range of debris area and mechanical response decreases.3.To improve the applicability of the theoretical analytical method,the mechanical response of the pipe on Pasternak foundation is derived by further considering the effect of soil shear stiffness.The reasonableness of the method is verified by comparison with existing studies.The effects of bending stiffness of pipe,pipe burial depth,pipe and tunnel angle and ground loss ratio on the uncoordinated deformation of the pipe and soil are analyzed.The results indicate that with the increasing of pipe modulus of elasticity and ground loss ratio,the angle between the pipe and tunnel,the length of separated area beneath the pipe,and decreasing of the burial depth of pipe,the influence range of the existing pipe settlement and the maximum mechanical response increase gradually.Conversely,the range of debris area and mechanical response decreases.