Research On The Influence Of Shield Tunnel Crossing Construction On Existing Bridge Pile Foundation Under Complex Geological Conditions

In this paper,based on Xuzhou Urban Rail Transit Line 2 phase I project xintaizihe station dingwanhe station tunnel under the dingwanhe bridge project,Using comprehensive analysis,numerical simulation,field measurement and other research methods and means,This paper focuses on the influence of shield tunnel Undercrossing on the existing bridge pile foundation under the complex geological conditions such as upper soft and lower hard stratum and karst cave,The relevant construction control technology and measures are discussed and analyzed,The research results can provide reference for shield tunnel construction under the same or similar engineering conditions in the future,It has a guiding role for the subsequent construction of Xuzhou Metro,The main results and conclusions are as follows:(1)Based on the engineering data,this paper discusses the risk control measures of shield construction under the complex conditions of soft upper and hard lower,karst cave development and crossing the existing bridge pile foundation.(2)Three dimensional numerical simulation software is used to simulate the construction process of shield tunnel crossing existing Bridge pile foundation under complex geological conditions,The stress and deformation of existing pile foundation during shield tunneling are analyzed,The horizontal displacement of the pile in the middle of the left and right tunnels has reverse shape,The horizontal displacement of the pile on the same side of the left and right tunnel has superposition form,During the construction of shield tunnel,the maximum axial force of pile foundation appears near the pile top,Due to the influence of shield excavation,the pile appears negative friction,and the axial force of pile near the excavation face of shield tunnel increases;In the case of pile foundation,the safety of the tunnel tends to decline;(3)The three-dimensional numerical calculation software is used to analyze the shield construction parameters,The influence of grouting range,grouting pressure,elastic modulus of grouting material,soil bin pressure and excavation sequence on the stability of existing pile foundation is studied,The laws of stress and deformation of pile foundation are summarized,It is suggested that the grouting range should be 270 °and the grouting pressure should be controlled within 0.4MPa ～ 1.0MPa.The pressure of soil bin should be controlled within 200 KPa.The settlement value of pile foundation caused by excavation first on the left side of tunnel is smaller than that caused by excavation first on the right side of tunnel,which is conducive to the protection of bridge structure,It provides the basis for the construction control measures of shield tunnel crossing the existing bridge pile foundation under complex geological conditions;(4)Through the construction site monitoring of shield tunnel crossing dingwanhe bridge section,the data of tunnel vault settlement,clearance convergence surface settlement and Bridge settlement are obtained,From the monitoring data,it can be seen that after the control measures are taken,the deformation of shield tunnel and pile foundation are effectively controlled,which shows that the above construction control measures have reference significance and great application effect in urban subway construction,and can provide valuable experience and data for the application of subway construction in the future.This thesis has 48 figures,5 tables and referred to 67 articles.