Research On The Existing Pipeline Deformation Influenced By Construction Of Opened-excavated Tunnel And Reinforcement Measures

Due to the acceleration of urbanization in China,the population is gradually concentrated in big cities,and the land resources in cities are increasingly tense.In order to maximize the use of urban space,underground space has gradually become a new direction of urban development.However,there are all kinds of underground pipelines in the urban area,so it is inevitable for foundation pit engineering to encounter the problems of adjacent existing pipelines,and these problems are gradually increasing with the passage of time.In order to meet the structure and use safety of the existing pipeline,and reduce the impact of foundation pit excavation on the existing pipeline,this paper mainly studies the deformation law of the lower existing pipeline under the disturbance of open cut tunnel foundation pit by using two methods of numerical simulation and theoretical calculation,combined with the foundation pit engineering of an intersection of a rapid reconstruction project in Shanghai.ABAQUS finite element software is used to study the influence of engineering factors on the deformation of existing pipeline.Combined with these laws,three reinforcement schemes are put forward,and the better scheme is selected to guide the design and construction.The main contents of this paper are as follows:(1)Based on ABAQUS simulation software,a three-dimensional finite element model is established to study the influence of upper foundation pit excavation on the deformation of existing pipeline.The vertical displacement curve of pipeline is drawn.The accuracy of the model is verified by comparing the theoretical solution,empirical formula solution,measured data and simulation results.(2)With the help of finite element software,the influence of excavation depth,plane size(length and width),pipeline factors(modulus and diameter),horizontal distance between two adjacent foundation pits,and vertical distance between pipeline and foundation pit on the deformation of existing pipeline is simulated and analyzed.The results show that these seven factors are positively correlated with the deformation value of existing pipeline,positively correlated with each other,positively correlated with each other,and positively correlated with each other Negative correlation,positive correlation,negative correlation,negative correlation.The excavation depth of foundation pit and the vertical distance between pipeline and foundation pit have significant influence on the deformation of pipeline.(3)Combined with the previous research results,aiming at the problems of relying on engineering examples,three reinforcement schemes are put forward,including pipeline stainless steel lining reinforcement,MJS soil reinforcement and pit bottom surcharge reinforcement.Through the comparison of simulation software,it is found that MJS soil reinforcement can improve the soil strength,and effectively reduce the maximum deformation value of the pipeline by controlling the soil deformation,but the control effect on the uneven settlement of the pipeline is small;Stainless steel lining reinforcement can effectively outline the modulus of the pipeline and reduce the uneven settlement of the pipeline;The pile load at the bottom of the pit can effectively reduce the vertical deformation and differential settlement of the existing pipeline,but it can only be reinforced after the excavation of the foundation pit.In view of this kind of project,the best scheme to control the pipeline deformation is to select MJS soil reinforcement and pipeline stainless steel lining reinforcement before the foundation pit excavation,and to carry out the pile loading at the bottom of the pit in time after the foundation pit excavation.