Numerical Analysis Of The Influence Of Open Excavated Foundation Pit Construction On Adjacent Bridge Pile Foundations

With the acceleration of my country’s urbanization process,the urban environment is becoming more and more complex,and the situation of underground engineering adjacent to existing structures has become the norm.It is of engineering significance to study the impact of tunnel foundation pit construction on adjacent bridge pile foundations.Based on the construction of the tunnel foundation pit of the high-speed main line of the Qianhai Project along the Yanjiang River in Shenzhen,this paper uses a combination of theoretical analysis and numerical simulation to study the influence of the excavation of the open-cut tunnel foundation pit in the land section and the water section on the adjacent existing bridge pile foundation.The main contents are as follows:(1)Summarize the current domestic and foreign research status on the impact of foundation pit excavation on adjacent bridge pile foundations,summarize the relationship between foundation pit excavation and adjacent soil outside the foundation pit,and summarize the experience based on actual engineering monitoring data Formula and theoretical derivation formula based on foundation pit dewatering and retaining structure constraints,and a two-stage method for calculating bridge pile foundation deformation.(2)Apply the finite element software Midas GTS/NX to establish a foundation pit excavation model,and perform numerical simulations based on the foundation pit support form of the designed section and the surrounding soil strengthening form,and the uplift of the foundation pit,deformation of the ground wall,etc.The various deformation laws are summarized,and the uplift disturbance range at the bottom of the foundation pit and the deformation laws of the underground continuous wall are obtained.The results show that the deformation shape of the foundation pit retaining structure is a lateral U shape.As the excavation depth increases,the maximum lateral displacement of the diaphragm wall increases,and the position of the maximum lateral displacement gradually moves upward,and the lateral displacement increases after each excavation.The amount is gradually decreasing.(3)The influence of the excavation of foundation pits in the land section and the water section on the pile foundations of adjacent existing bridges is studied separately,and the development law of the displacement and internal force of the existing bridge pile foundations with the excavation of the foundation pit is obtained.The results show that the bottom of the left pile foundation of the existing bridge is basically not displaced,and the total displacement basically assumes the form of a small lower part and a large upper part.The magnitude of the vertical displacement of the pile foundation is in the order of hundredths of a millimeter,which has a large numerical difference compared with the horizontal displacement.The pile foundation bending moment of No.1 pile is obviously larger than that of other piles.A positive bending moment appears in the upper half of the pile foundation,and there is a maximum positive bending moment about a quarter below the top of the pile foundation.For the simulated working conditions of foundation pit excavation in water area,the horizontal displacement value of No.1 pile appears inverted point at the buried depth of 6m.The horizontal displacement and deformation of the right pile foundation are basically the same,which is 56%smaller than that of the No.1 to No.3 piles under the left pile cap.The pile foundation bending moment of No.1 pile is obviously larger than the other piles.A positive bending moment appears in the upper half of the pile foundation.There is a maximum positive bending moment about a quarter below the top of the pile foundation,and a reverse bending point appears in the middle of the pile foundation.,Negative bending moment appears in the lower part of the pile foundation,and two extreme values of negative bending moment appear in the lower part of the pile foundation.(4)Select the support strength in the foundation pit,the thickness of the diaphragm wall,and the degree of pile-soil strengthening as typical parameters,conduct three-factor and threelevel orthogonal tests to study the influence of the three parameters in the excavation engineering of adjacent bridge pile foundations.And obtain the optimal combination of the influence control of the excavation of the foundation pit in the water area on the adjacent bridge pile foundation.The order of the degree of influence of the three factors on the horizontal displacement of the existing bridge pile foundation is: the support strength in the foundation pit> the thickness of the underground continuous wall> the pile The degree of soil strengthening.The support strength in the foundation pit has the greatest influence on the maximum horizontal displacement of the existing pile foundation caused by the excavation of the foundation pit.