Study On The Influence Of Deep Pit Excavation On Existing Pipeline Deformation

It is a great engineering application value to study the influence law of the surrounding pipelines and the disaster control measures in the deep excavation of metro vertical shaft pits.In this paper,relying on the deep foundation pit engineering of a certain tunnel in Xi'an metro,the research work was carried out by means of theoretical analysis,numerical simulation and on-site monitoring.The main contents and conclusions are:(1)The investigation of the existing underground pipelines along the Xi'an metro line 5 was completed by site investigation method.The deformation mechanism of the existing pipelines induced by excavation of deep foundation pits in the shaft was studied.The common failure modes of the existing pipelines due to excavation of deep foundation pits were given.The causes of damage were analyzed,and the control standards for the existing pipeline deformation caused by excavation of deep foundation pits were proposed..(2)The main factors influencing the deformation of existing pipelines caused by excavation of deep excavation in subway shafts are engineering geology and hydrogeological conditions,pit excavation geometry,pit excavation support type and construction period,pipeline usage,and pipeline material.Pipe diameter,pipeline interface type,service life of pipelines,construction quality,and the spatial relationship between pipelines and foundation pits.(3)Using FLAC3D numerical simulation software to establish a three-dimensional calculation model,taking into account the deep excavation depth of the shaft pit,the pipeline material,the spatial relationship between the pipeline and the foundation pit and other working conditions,completed the effect of shaft deep excavation on the existing pipeline deformation the study.The results of the study show that the deformation of existing pipeline induced by excavation of deep foundation pit is significantly affected by the pit corner effect.The deeper the deep excavation of vertical shaft pit is,the more obvious the deformation of the pipeline is;the deformation of different pipe materials is PVC pipe,cast iron pipe and concrete pipe in descending order;the influence of pipeline buried depth on its deformation and the deformation of strata and support structure.The erection position is closely related;the vertical displacement of the pipeline increases with the distance from the pit wall,then increases first and then decreases,and the horizontal displacement continuously decreases.Based on the law of the effect of excavation of deep foundation pits on the existing pipelines,corresponding safety control measures for existing pipelines are given.(4)Based on the shaft deep foundation pit project of Xi'an Metro tunnel,the design of the deep foundation pit dewatering plan and the formulation of the monitoring plan were completed.The FLAC3D numerical simulation method is used to analyze the deformation of the retaining structure,surface and existing pipelines induced by excavation of deep foundation pits.The measured deformation is basically consistent with the simulation results.