| With the rapid development of underground rail transit construction and underground With the rapid development of underground rail transit construction and underground space,the surrounding environment of deep foundation pit engineering of subway stations has gradually shown a more complicated trend,especially during the construction of deep foundation pits in water-rich karst formations.Due to insufficient research on the degree of deformation control,it is easy to cause adverse effects on the surrounding environment.In this paper,based on the deep foundation pit project of the Houyan Station of Dalian Metro Line 5 and relying on the China Railway Seventh Bureau Group Science and Technology Research and Development Project(18A22),the study on the influence of deep foundation pit excavation in water-rich karst formation on the deformation of adjacent viaduct piers has been carried out.The main research contents are as follows:(1)Summarize the calculation method of ground settlement caused by foundation pit dewatering and the influence factors of foundation pit excavation on the deformation of adjacent bridge piers,and analyze the two-stage deformation prediction method of adjacent structures during the construction of foundation pit,providing certain technical support for the research on the influence of bridge pier deformation.(2)Aiming at the deep foundation pit project of the Houyan Station of Dalian Metro Line5,a three-dimensional finite element numerical model of the impact of deep foundation pit excavation on adjacent viaduct piers under the condition of fluid-solid coupling was established,and the deformation laws of deep foundation pits and adjacent viaduct piles under dewatering conditions and excavation conditions were studied respectively.The results show that the change trend of the displacement field generated by each precipitation deformation condition and the corresponding excavation condition and the surface settlement value outside the pit are roughly the same.The surface settlement curve outside the well section and the standard section pit roughly presents a groove-shaped settlement distribution.The horizontal displacement of the support structure shows a spindle shape change trend along the depth direction,and the horizontal displacement change trend of the support structure under the precipitation deformation condition of step n(2≤n≤4)is basically the same as that of the excavation condition of step n-1.With the gradual increase in the depth of the bridge piles,the horizontal displacement of the pile foundation of the bridge pier presents a trend of larger at the upper end and smaller at the lower end.The horizontal displacement of bridge pile has a positive correlation with the excavation depth of deep foundation pit,and the deformation and internal force of viaduct pier are within the safe control range.(3)The deformation monitoring plan for the deep foundation pit engineering of the Houyan Station was compiled and on-site measurement was carried out.The deformation law of the deep foundation pit and adjacent bridge piers during the construction process was analyzed.The results show that the comparison and analysis between the simulated value and the measured value verify the accuracy and rationality of the numerical model.With the continuous advancement of deep foundation pit construction conditions,the horizontal displacement of the supporting piles shows a "bow-shaped" change trend that first increases and then decreases.The change rate of the maximum horizontal displacement of the supporting piles gradually slows down and tends to be stable with the excavation of the deep foundation pit.The differential settlement value of the bridge pier basically shows a change phenomenon that fluctuates around the critical value between ascent and subsidence,and the horizontal displacement curve of the pier generally shows a phased decrease trend.(4)By changing the design parameters such as the distance between the bridge piers and the deep foundation pit,supporting stiffness conditions and geological conditions,the influence of deep foundation pit excavation on the displacement of adjacent pier tops and pier pile foundations was quantitatively analyzed and the law of displacement of adjacent bridge piers is studied in detail.The distance between the bridge pier and the deep foundation pit,the support stiffness and the elastic modulus of the first layer of soil show a negative correlation with the horizontal displacement of the pier pile foundation,and the relationship between the horizontal displacement of the top of the pier and the elastic modulus of the first layer of soil presents an "L" shaped trend. |
