Research Of Interaction Between Deep Foundation Pit And Adjacent Existing Intercity Railway

With the expansion of the national intercity railway network as well as the large-scale constructions of foundation pit engineering, problems are inevitably encountered which involve interaction between deep foundation pit and adjacent existing intercity railway during construction period. These problems have aroused engineers’extensive attention. In this paper, static and dynamic analysis models are established for the study of interaction between deep foundation pit excavation and adjacent existing intercity railway using large finite element software ABAQUS. The study is based on the foundation pit support project of Xiaohongshan passenger station in Nanjing which is in the vicinity of Shanghai-Nanjing intercity railway.The main contents and results are as follows:(1) Finite element model is established based on the actual conditions of Xiaohongshan passenger station foundation pit engineering. The characteristics of double-row pile support structures under excavation and dynamic loadings as well as the dynamic response characteristics of subgrade are analyzed. Calculation results and in-situ monitoring data are compared to verify the validity of the model.(2)The internal force and deformation of double-row piles as well as surface deformation under five kinds of train speed, namely150km/h,200km/h,250km/h,300km/h and350km/h, are compared and analyzed. Results show that with the increase of train velocity, bending moment of piles increases significantly, and the horizontal displacement of piles and the subsidence and uplift of ground increase slightly.(3) Based on the analysis of internal force and deformation of double-row piles as well as surface deformation under conditions of different distance between foundation pit and railway, it is suggested that the influence of intercity railway should be considered in engineering design if the distance is within four times of the excavation depth of foundation pit.(4)The dynamic responses in X and Y direction under different conditions are analyzed. These conditions are:①double row pile supporting with reinforcement of the passive area and②double-row piles supporting only. Results show that compared with condition②, condition①exhibits significant decrease of the adverse effects caused by the pit excavation, such as lateral deformation and settlement of railway subgrade.(5) The deformation, vibration characteristics and dynamic stress of subgrade under different excavation depth are analyzed. Results show that the influence of excavation depth on the subgrade are mainly reflected by the increase of lateral displacement, vertical subsidence of subgrade, differential settlement and the tensile stress in X direction of subgrade bed surface.