Study On The Influence Law And Control Of Xi’an Metro Tunnel Construction On Pipeline Deformation

Urban metro tunnels will inevitably cross a large number of existing underground pipelines.Construction disturbance would produce additional internal force and deformation to the pipelines overlying the tunnel,which would seriously affect the safe use of existing pipelines.In order to ensure that the metro tunnel can be constructed safely and orderly on the premise of safe use of pipelines,it was urgent to study the influence law and control standard of metro tunnel con struction on the deformation of existing pipelines.Base on the taking Xi’an metro project,this paper was constructed the prediction model of stratum settlement under the influence of metro tunnel construction and the prediction model of pipeline stress and deformation under the influence of pipe soil separation,and put forward the deformation control standard of existing pipeline under the influence of Xi’an metro tunnel construction.The main research results were as follows:(1)Based on the random medium theory,the prediction model of formation deformation induced by metro tunnel construction was established,and the numerical simulation method was used to analyze and explore the characteristics of formation settlement induced by metro tunnel under the existing pipeline.The analysis shows that under the influence of tunnel excavation,the existing pipeline has a certain inhibitory effect on the ground settlement above it,especially the greater the stiffness is,the more obvious the inhibitory effect is.Therefore,when the pipeline stiffness is large,the surface settlement value cannot be used to replace the pipeline settlement.(2)The deformation under the interaction between pipeline and soil was divided into three stages:pipe-soil close contact,pipe-soil separation critical point and pipe-soil separation.The prediction model of pipeline deformation considering pipe-soil separation and a prediction model of pipe-soil separation range under orthogonal and oblique crossing conditions were established.It was obtained that the pipe-soil separation range induced by tunnel construction in a section of Xi’an metro line 1 was the pipeline within the horizontal distance of 16.272m(both sides of the tunnel center line are 8.136m),and the maximum pipe-soil separation gap was 4.2mm.(3)Based on the established prediction model of pipeline deformation considering the influence of pipe-soil separation,the influence laws of main factors such as relative position of pipe parts,pipeline material,pipe diameter and buried depth of pipeline on pipeline stress and deformation are analyzed.At the same time,the deformation law of overlying pipeline under the disturbance of subway tunnel construction was studied by numerical simulation method.The results shows that under the influence of subway tunnel construction,there is pipe-soil separation between the existing pipeline and the stratum,and the pipe-soil separation range is 1.5 times the tunnel diameter above the tunnel vault.When the relative position of pipe-tunnel,buried depth of pipeline,material,diameter and other factors are determined,the pipeline rotation angle can be used as the key parameter to control pipeline deformation.(4)The typical geology along the Xi’an metro line 1 tunnel was divided into three categories.Based on the obtained pipeline stress deformation model considering the influence of pipe-soil separation,combined with the pipeline instability checking calculation.Exploration of pipeline control standard are conducted from three main parameters of maximum pipeline angle,maximum allowable surface settlement and maximum allowable surface inclination rate.The control standard of different buried depth,material and pipe diameter in the construction of Xi’an metro were obtained.(5)Based on the existing pipeline deformation prediction model considering the influence of pipe-soil separation and the pipeline deformation control standard under the influence of Xi’an metro construction.The safety assessment of important pipelines in three types of sites of Xi’an metro line 1 was completed by theoretical calculation and numerical simulation.Specific reinforcement and protection measures were proposed for pipelines with potential safety hazard.The field monitoring results show that the pipeline deformation control standards and reinforcement measures formulated in this paper are reasonable and effective,which provides a scientific basis for preventing and controlling the deformation and failure of the overlying pipelines induced by subway tunnel construction.