Study On Influence Of Excavation Of Subway Deep Foundation Pit On Buried Pipelines

With the development of urbanization,subway has become one of the important tools to solve urban congestion.Metro often traverses busy cities.The construction of Metro must consider its impact on the surrounding environment,especially on the surrounding buried pipelines.Under such complicated conditions,not only the stability and safety of pit itself,but also the deformation and displacement of the surrounding environment should be controlled.Based on the above considerations,this paper analyses the excavation of a subway foundation pit from three aspects: theoretical study,field measurement and numerical simulation.The main work and results are as follows:1.Learning the deformation mechanism,influencing factors and control criteria of foundation pit and pipeline,based on the theory of elastic foundation beam,the deformation trend of pipeline along the length direction of foundation pit is predicted simply.2.Collect and analyze cases of foundation pit,to analyze the development of surface and pipeline settlement with time,with excavation,with the maximum settlement and the distribution law of settlement,and to summarize the influence law of surface settlement and pipelines with excavation;put forward the average maximum surface settlement is 0.23%H,the maximum is 5.5%H,which is about0.5H outside the pit wall;the average maximum settlement of pipeline is 1.24%H,the maximum is 2.5%H,which is about 0.75 H outside the pit wall.The maximum surface subsidence is twice as large as that of pipeline,and the position of maximum displacement is similar to that of pipeline,and the position and size of mutation point are similar.3.Based on practical engineering,a PLAXIS three-dimensional numerical model is established by HSS constitutive model.The spatial distribution and time-history development law of pipelines during the excavation are analyzed,andit is concluded that the maximum horizontal displacement and vertical displacement of pipelines are distributed near the middle of the pit.Near the end wells of the foundation pit,the displacement change rate of the pipeline is more than 10%,and the displacement varies greatly.The displacement of the pipeline at this position should be monitored emphatically.4.Discuss the different factors which influence the displacement of pipelines.Among which,the influence range of horizontal and vertical displacement increases with the excavation;pipeline displacement is the largest at 0.78 H distance from pit.The maximum horizontal displacement increases with the increase of buried depth,and the vertical displacement of pipelines is less affected by buried depth.The effect of full hall reinforcement is better than that of the skirt,and the reinforcement effect is better in controlling maximum horizontal displacement than in vertical displacement of pipeline in excavation.Within 6meters of reinforcement depth,the deeper the reinforcement depth,the better the effect of restricting pipeline displacement.The development of pipeline displacement can be limited by adjusting the supporting and reinforcing soil.The above discussion provides a reference for the calculation and prediction of pipelines by using three-dimensional numerical simulation and other similar projects.