The Deformation Control Of A Subway Station Under The Influence Of A Deep And Large Foundation Pit Construction With Composite Support System

With the continuous advancement of urbanization,the development model of "real estate + subway" has led to an increase in the number of projects adjacent to the subway station in the foundation pit of the deep and large building.To ensure the safe operation of subway trains,more complex supporting systems are often used in the design of deep and large foundation pits.However,there is a lack of research on the deformation law of the complex support system itself and its influence on the adjacent underground structure during the construction of foundation pits.Therefore,it is particularly urgent to study the influence of this kind of engineering construction on the deformation of adjacent subway stations.The excavation depth of a deep and large foundation pit of a composite support system is 25.5m,the minimum clear distance from the main structure of the station is10.6m,and the closest distance to the entrance and exit structure is only 3.6m.Relying on this project,numerical simulation,on-site monitoring and other methods are used to study the morph of the self-supporting system,the ground settlement and the subway station under the construction.Then the influence of different support parameters on the morph of the subway station and track is analyzed,and the internal relationship between the deformation value of the station and track and the support parameters is further discussed.The main work and achievements are as follows:(1)Relying on the new project,a three-dimensional finite element model of foundation pit-soil-station-track is established.Through calculation and analysis,it is concluded that due to the effect of internal support,the deformation of the foundation pit retaining pile is larger in the middle and smaller at the heads in the vertical direction of the pile body,and the maximum horizontal displacement is located at about 0.6 times the excavation depth.The area affected by the construction is within 1.3 times of the excavation depth,and the surface settlement trend is in a "V" shape.With the excavation and construction of the subway station,it continues to rise to the side of the foundation pit,and the vertical and horizontal deformation trends of the station and track are all in the shape of "∩".The excavation of the foundation pit has little influence on the geometry of the track.(2)Through field measurement and analysis,the morph history of the station and track in the excavation is studied.The results show that the inner-brace + pile-anchor composite support structure has better control over the deformation of adjacent stations and tracks,and can ensure the safe operation of subway trains.Comparing the analog value of station and track morph with the measured data,it is concluded that the simulated and measured morph trends keep consistency,and the maximum deformation value corresponds to the middle position of the foundation pit.This verifies the rationality and reliability of the composite support system model.(3)The analysis of the influence of different support parameters on the maximum deformation value of the subway station and track shows that the morph of the station and track is less affected by the pile diameter of the retaining pile and the size of the internal support section.It is greatly affected by the embedding depth of the retaining pile and the number of support channels.It is suggested that the optimal parameters should be a pile diameter of 1.0m,an embedded depth of 8m,4 internal supports and an internal support section of 1.0m×1.0m.(4)Through the calculation of 50 working conditions where the support parameters cross,the relationship between the adjacent subway station and track deformation and the support parameters is further studied,and the three-dimensional relationship is fitted.The results show that when the embedding depth of the retaining pile is greater than 8m,the maximum deformation of the station and track will float in a smaller range as the diameter of the retaining pile increases.When the number of internal support is greater than 4,the maximum deformation of the station and track structure will float within a smaller range as the cross-sectional size of the internal support increases.