Research On Influence Of Foundation Pit Construction Of Subway Station On Pile Foundations Of Adjacent Existing Viaduct

Urban rail transit is limited by the narrow space and complex surrounding environment,which inevitably has a negative impact on the surrounding environment during construction.The impact of subway station foundation pit construction is particularly serious.Existing research focuses on ensuring the stability of the foundation pit and controlling the deformation of the supporting structure of the foundation pit.The influence of the entire process of subway station foundation pit construction on the adjacent existing pile foundation is still rare,especially for the deformation of foundation pits supported by servo steel.In order to study the influence of the deep foundation pit construction of the subway station on the pile foundation of the adjacent Viaduct,this paper relies on the foundation pit engineering of Yingtian Road Station of Nanjing Metro Line 7 to carry out research on.The main conclusions are as follows:(1)This paper theoretically analyzes and derives the calculation formula of pile foundation settlement of the adjacent viaduct caused by waterproof curtain supplemented with well point dewatering pattern,and the differences between the two schemes of the drop waterproof curtain and the suspended waterproof curtain are analyzed and compared.With the excavation of the foundation pit,the settlement of the pile foundation of the viaduct outside the foundation pit increases exponentially with the excavation depth of the foundation pit.For Yingtian Road Station foundation project,when the buried depth of the underground diaphragm wall is 40 m,the theoretical settlement of the pile foundation of the Yintian Road Viaduct should be as high as 17.2mm when the foundation pit falls below the design elevation.(2)Based on the incremental method,the prediction of the foundation pit supporting structure deformation under the condition of servo steel support,the calculation formula of the displacement of the adjacent pile foundation caused by the deformation of the underground diaphragm wall is derived.Active servo steel support can effectively control the deformation of the underground diaphragm wall to reduce the surrounding soil disturbance,thereby reducing the impact on the adjacent pile foundation.As the axial force threshold of the servo steel support increases,the displacement of the adjacent pile foundation decreases,but the bending moment of the underground diaphragm wall at the support point also increases.Therefore,the deformation and internal force of the diaphragm continuous wall should both be considered in the design.(3)Analyzing the field monitoring data,comparing the deformation modes of the underground diaphragm wall between the servo steel support section and the prestressed steel support section.The underground diaphragm wall of the servo steel support section is greatly suppressed at the supporting point of the servo steel support.With the excavation of the foundation pit,the deformation mode of the underground continuous wall is not single;while the deformation of the underground diaphragm wall of the prestressed steel support section has always been in the shape of "convex".The deformation of the underground diaphragm wall of the servo steel support section is smaller than that of the prestressed steel supported underground continuous wall.(4)Establishing three-dimensional finite element models to analyze the structural parameters that may reduce the impact of excavation on the pile foundation of the adjacent viaduct.The numerical simulation results preliminarily verify the correctness of the theory of deformation prediction of underground diaphragm wall supported by servo steel.Increasing the thickness of the underground continuous wall,using more rigid concrete support and using servo steel support can reduce the impact of excavation on the pile foundation of the adjacent viaduct.For Yingtian Road Station foundation project,the effect of increasing the thickness of the wall to reduce the impact on the viaduct is not as good as the effect of using a servo steel support system.When the thickness of the underground continuous wall is 800 mm,the servo steel support system has the best effect of suppressing the deformation of the foundation pit.The maximum horizontal displacement of the viaduct pile foundation is only 1.5mm;when one concrete support + three steel supports are used,As the thickness of the underground continuous wall increases,the maximum horizontal displacement of the viaduct pile foundation decreases accordingly.When the thickness of the underground continuous wall is 1200 mm,the maximum horizontal displacement of the viaduct pile foundation is 1.68 mm.