Analysis Of Influence Of Deep Foundation Pit Excavation On Deformation Of Adjacent Underground Pipelines In Metro Station(Taking Xinfadi Station As An Example)

With the development of cities in China,subway has become the most convenient mode of transportation.However,with the continuous increase of subway construction,subway projects have increasingly higher requirements on the surrounding environment.In the process of construction,the subway may pass through the sensitive underground pipeline,which will cause certain influence on the pipeline.Therefore,the research on the influence of the excavation of subway station foundation pit on the deformation of the surrounding underground pipeline has become an important topic.In this paper,the deformation of adjacent underground pipeline caused by deep foundation pit excavation in Xinjafadi Station of Beijing Metro Line 19 is studied.Based on the analysis of field investigation data,by means of in-situ monitoring and numerical simulation,the deformation law of foundation pit and pipeline,the influence of different factors on pipeline deformation and the relationship between pipeline deformation and soil deformation in corresponding positions without pipeline are analyzed,and the following conclusions are drawn:(1)The surface settlement data,pile lateral movement data and pipeline settlement data were collated and analyzed.According to the monitoring data,the surface settlement law outside the pit is "grooves",and the maximum settlement appears at a certain distance from the enclosure structure.The lateral displacement curve of retaining pile shows a "parabolic shape",and the position of the maximum lateral displacement decreases gradually with the increase of the excavation depth.The settlement value of the pipeline increases with the increase of the depth of the foundation pit,and the further away from the center of the short edge of the foundation pit,the smaller the settlement value of the pipeline.(2)MIDAS /GTS NX software was used to build a three-dimensional finite element model of pipe-soil-foundation pit,and the excavation process of foundation pit was simulated and restored.The calculation results show that the soil heave occurs after the foundation pit excavation,and the maximum value appears at the center of the bottom of the foundation pit.The surface of the pit produces a "settlement trough",and the maximum settlement appears at a certain distance from the retaining structure.The horizontal displacement of soil outside the foundation pit towards the direction of the foundation pit is distributed symmetrically on both sides of the foundation pit.With the excavation of the foundation pit,the pipeline’s anisotropic deformation is increasing.The reliability of the model is verified by comparing the simulated values of soil displacement and pipeline settlement with the monitored values.(3)The influence degree of different factors on pipeline deformation was compared.It is found that increasing the elastic modulus of the pipeline,the compression modulus of the soil around the pipeline,the buried depth of the pipeline,the distance between the pipeline and the foundation pit and the stiffness of the connecting wall can reduce the deformation of the pipeline.The pipeline material,the buried depth of the pipeline and the stiffness of the connecting wall have great influence on the vertical displacement of the pipeline.The soil quality around the pipeline and the distance between the pipeline and the foundation pit have great effects on the horizontal displacement of the pipeline.To provide reference basis for the same type of project.The deformation law of soil in the corresponding position with pipeline deformation and without pipeline is studied from two aspects of different distance and different buried depth from the foundation pit.Both deformations are the same,and the pipeline deformation is greater than that of soil without pipeline.In order to avoid the pipeline damage,some pipeline protection measures are put forward.