Study On Mechanism Of Pile Bearing Process Affecting Near Existing Metro Tunnels

In recent years,with the development of cities in China,the demand of subways and high-rise buildings is increasing.With the emergence of more and more high-rise buildings around the subway,the connection between subway tunnel and pile foundations is growing.If the bearing pile foundation has too much influence on the adjacent subway tunnel,it will cause problems such as cracking and seepage in the tunnel,which will inevitably threaten the safe operation of the subway.Therefore,research on the impact of bearing pile foundations on subway tunnels has become a hot topic in the engineering field.The pile foundation around subway will have some influence on the stability of tunnel structure under the action of the upper load.This paper aims to study the mechanism of the impact of pile foundation on adjacent subway tunnels.Abaqus is used to analyze the influence of bearing pile foundation on the stress and deformation of tunnel.With the help of the 60 gt centrifugal model test system of Chang'an University,a pile-soil-tunnel model is constructed in accordance with the actual situation.A variety of stress displacement monitoring components are used to monitor the distribution,bending moment and earth pressure around the tunnel under different working conditions.The paper mainly draws the following research results:(1)To improve work efficiency,a new method of building finite element model is proposed,which is based on BIM technology.The model is built in Revit,with the Second development of Revit,a program interface is compiled,which is between Revit software and large finite element software Abaqus.The conversion of the BIM model to the finite element model is realized,and the preparatory work for the structural calculation of the BIM model is completed.(2)Three-dimensional finite element analysis of soil displacement,tunnel deformation,tunnel bending moment and stress under the condition of single pile bearing is carried out.The influence of design parameters such as pile length,the distance between pile and tunnel,upper load,the mode of pile laying and tunnel lining stiffness on the tunnel under single pile condition is analyzed.Pile-soil-tunnel interaction mechanism is analyzed.(3)Using Abaqus software to simulate the effect of group piles on tunnels underload.The influence of piles spacing and the size of group size on tunnel under pile group working condition is analyzed.The applicability of two-dimensional plane strain finite element analysis in this simulation is analyzed.Some protection measures for tunnels are proposed.The two-dimensional analysis of the shielding effect of the isolation pile is carried out,and the design parameters of the isolation pile are proposed.(4)With the help of the 60 gt centrifugal model test system of Chang'an University,an indoor centrifugal model test is carried out to analyze the deformation,bending moment and earth pressure of the tunnel under various working conditions,and the influence of pile length,pile tunnel spacing and upper load on the tunnel are analyzed.The results are verified with those of finite element software.Through finite element calculation and centrifugal model test,a series of analyses are made on the influence of bearing pile foundation on nearby subway tunnels.The protection measures of tunnels are studied.Through these studies,some reasonable suggestions can be made for the early design of the pile foundation around the subway tunnel and the later operation of subway.