Study On Deformation Law Of Open-pit Foundation Pit Of A Starting Of A Shield Tunnel In Beijing Subway

At present,many cities in China vigorously develop rail transit.As a new,efficient and green public transport,subway plays an increasingly important role in alleviating the diseases of big cities.Especially in Beijing and Shanghai,which have tens of millions of people,the existence of subway is indispensable.At present,36 cities have built and opened metros in China.The total mileage of metro operation in China has reached 5033 kilometers.The total mileage of metro operation in Beijing is 636.8 kilometers.There are 19 Metro lines.The daily passenger traffic volume is 12.411 million,which greatly alleviates the traffic congestion in Beijing.It is expected that by 2020,the total mileage of Beijing Metro will reach 1177 kilometers,and the development of rail transit will continue to increase throughout the country in the future.There will be a large number of foundation pit projects in subway construction.If the design and construction scheme are unreasonable,it may have more serious consequences.Based on an open-cut foundation pit project of a shield tunneling starting well in a section of Beijing Metro New Airport Line(referred to as a foundation pit in M1 section for short),this paper first introduces the research status of foundation pit deformation analysis,compiles a construction monitoring scheme according to design data and specifications,and also analyses the monitoring data on site.In addition,the characteristics of MIDAS GTS/NX finite element software are introduced,and the application of MIDAS GTS/NX finite element software is described.The software simulates the excavation process of the foundation pit,analyses the deformation law of the foundation pit,and optimizes the design and Simulation of the supporting structure of the foundation pit by using the software.In addition,there are many factors affecting the deformation of the retaining structure and surrounding buildings of the foundation pit.Using the method of system analysis to predict the deformation of the foundation pit can make up for some shortcomings of empirical formula and numerical simulation analysis method.The main research results of this paper are as follows: By comparing the measured results with the numerical simulation results,the accuracy of the model is proved;through the analysis of the field monitoring data,the final settlement curve of the monitoring section is a parabola upward from the opening,the horizontal displacement curve of the pile body in the steel support section is a "bow" curve moving parallel,and the anchor cable support section is a "S" curve.In the space effect of foundation pit,the deformation of short side is less than that of long side;the insertion ratio and the inclination angle of anchor cable are studied by using MIDAS GTS/NX finite element software,and it is concluded that the insertion ratio is between 1:4 and 1:5.5,and the inclination angle of anchor cable should be between 10 and 20 degrees.The prediction model of foundation pit deformation based on BP neural network is established,and the results are compared with the measured values through the implementation of MATLAB.The difference between the two models is small.The model can accurately predict the short-term horizontal displacement of piles and the settlement of surrounding surface.