Response Of Adjacent Pile Foundation Caused By Shield Excavation Under Different Vertical Loads

With the continuous construction of subway lines in various cities in China,shield tunnel inevitably passes through the pile foundation of houses and bridges,which adds new challenges to shield construction.In this paper,taking the pile foundation of a subway side crossing bridge in Zhengzhou as the engineering background,the pile deformation,internal force simulation and measured calculation results during shield construction are compared and analyzed,and the whole process of shield construction is simulated by Midas software,and the response mechanism of pile foundation under different vertical loads on the top of pile cap is obtained,and the deformation and internal force of pile foundation under three different influencing factors are further studied The law of change.The main research contents and achievements are as follows(1)This paper systematically introduces the research status of shield tunnel construction on Soil and adjacent pile foundation,briefly analyzes the ground settlement mechanism caused by shield construction,and studies the variation law of internal force and deformation of adjacent pile foundation caused by shield tunnel construction combined with the mechanism of pile foundation load transfer.(2)According to the analysis of the field monitoring,the horizontal displacement and steel stress of the upper part of the pile foundation are obtained,and then the axial force and bending moment of the upper part of the pile foundation are obtained by the principle of stress superposition.The results show that: the axial force,horizontal displacement and bending moment curves of the front row piles and the back row piles are basically consistent,and the internal force and deformation curves of the same row piles are basically coincident,and the values of the front row piles are larger than those of the back row piles.(3)Midas software is used for numerical simulation,and the simulation and measured calculation results of pile internal force and deformation are compared and analyzed when the vertical load on the top of pile cap is 0.On this basis,the internal force and deformationlaw of pile body caused by shield excavation under different vertical loads of pile cap top are studied.The results show that the numerical simulation values of vertical displacement,axial force,horizontal displacement and bending moment are basically consistent with the measured values,which verifies the reliability of the numerical simulation in this paper.Different vertical loads on the top of pile cap have great influence on the vertical displacement and axial force of pile body,but have little effect on the horizontal displacement and bending moment of pile body.When the vertical load on the top of pile cap is less than 180 kPa,the vertical compression deformation of pile body is small.When the vertical load is greater than 180 kPa,the vertical compression deformation of pile body above the tunnel center line increases gradually.(4)The three-dimensional finite element model is established by Midas software.Considering three factors of tunnel buried depth,stratum loss ratio and pile tunnel spacing,the variation rules of vertical displacement,axial force,horizontal displacement and bending moment of pile shaft are analyzed.The following conclusions are drawn: the influence of tunnel buried depth and stratum loss ratio on deformation and internal force of pile shaft is greater,while the influence of pile tunnel spacing is relatively weak The internal force and deformation curve trend and numerical value of pile body with the same tunnel depth are quite different.When the tunnel depth is less than 16 m,the axial force of pile body increases slowly first,then decreases sharply,and finally decreases slowly;when the tunnel depth reaches 24 m,the axial force of pile body shows a linear decrease rule.