Study On The Influence Of Shield Tunnel Construction On Existing Underground Pipelines

Subway tunnel construction will inevitably have a certain impact on the surrounding environment,especially when there are underground pipelines around,often lead to safety accidents.As a people livelihood project,the destruction of pipelines will not only cause huge economic losses,but also have serious social impact.Therefore,it is of great practical significance and far-reaching theoretical significance to study the deformation law of pipelines caused by subway tunnel construction and its in-situ protection technology.On the basis of summarizing and analyzing the influence of urban excavation engineering on surrounding soil and underground pipelines at home and abroad,a three-dimensional model of pipeline-soil-tunnel interaction is established by FLAC^3Dnumerical simulation software.Considering the factors of pipeline material,diameter,soil properties of underlying layer,pipeline buried depth and buried distance,the influence of subway tunnel excavation engineering on the displacement and internal force distribution of parallel and orthogonal underground pipelines is studied.In addition,based on a subway project in Tianjin,combined with field monitoring data,the influence of tunnel excavation on existing underground pipelines under specific conditions is analyzed.The main conclusions are summarized as follows.（1）Tunnel excavation has obvious influence on the displacement of adjacent underground pipelines.The vertical displacement of the horizontal pipeline increases along the axial direction,and reaches the maximum at the far end of the pipeline.The horizontal displacement can be ignored.The vertical displacement curve of the orthogonal pipeline is similar to the surface settlement curve,reaching the maximum settlement at the center of the pipeline.The horizontal displacement moves towards the tunnel excavation at both ends of the pipeline,and moves towards the opposite direction of the tunnel excavation,reaching the maximum at the tunnel position.（2）Tunnel excavation has obvious influence on the internal force of the pipeline,and the longitudinal bending moment of the pipeline is basically symmetrically distributed along the axis.The first 1/2 section of the parallel pipeline has obvious flexural deformation.The flexural deformation at both ends of the orthogonal pipeline is large,and the flexural deformation in the middle is small.The pipeline has an inward warping deformation up and down,and an outward warping deformation around.It can be seen from the numerical results that the deformation of parallel pipelines is dominated by warping,and that of orthogonal pipelines is dominated by bending.It can be seen from the axial force that the parallel pipeline is in a compression state,and the orthogonal pipeline is compressed outside the tunnel diameter range and tensioned within the tunnel diameter range.（3）The displacement of pipelines with different materials after tunnel excavation is roughly the same.The greater the stiffness of the pipeline is,the stronger the resistance of the pipeline to soil deformation is,and the additional stress and bending moment generated are larger.Different diameter has little effect on pipeline displacement,and the internal force of pipeline increases with the increase of diameter.（4）The vertical displacement and horizontal displacement of pipeline decrease with the increase of soil elastic modulus,cohesion and internal friction angle.The longitudinal bending moment of parallel pipeline decreases with the increase of soil elastic modulus,and increases with the increase of soil cohesion and internal friction angle.The longitudinal bending moment and intermediate tension of the orthogonal pipeline decrease with the increase of elastic modulus,cohesion and internal friction angle of the soil,and the circumferential bending moment is less affected by soil change.（5）The vertical displacement of pipeline increases with the increase of buried depth,and decreases with the increase of horizontal distance from the tunnel.The horizontal displacement of pipeline far from the tunnel changes significantly.Near the tunnel,the internal force of the pipeline fluctuates with the excavation of the tunnel.The longitudinal bending moment,circumferential bending moment and axial force of the pipeline increase.Different horizontal distances from the tunnel lead to the rotation of the pipeline warping deformation to the tunnel side.