Study Of Influence On Vertical Displacement Of Existing Tunnel And Lateral Displacement Of Bridge Pile Foundation By Deep Excavation Construction

In recent years,with the rapid development of China's economy,more and more deep foundation pit projects appear in urban areas.During the excavation of these foundation pits,it is very likely that they will cross and collide with existing tunnel structures and bridge structures,under the unloading action of foundation pit excavation,vertical displacement will occur in existing tunnels below and lateral displacement will occur in adjacent bridge piles,which seriously affects the structural safety.This paper is based on a comprehensive corridor project,the influence of foundation pit excavation on vertical displacement of existing tunnel below and lateral displacement of adjacent bridge piles is studied mainly by the methods of numerical researches and field measurement.In this paper,the main research work and achievements include:(1)Two kinds of elastic foundation beam models are introduced to calculate the vertical displacement of existing tunnels below after unloading of foundation pit excavation,and theoretical formulas are obtained,the method of determining equivalent stiffness of tunnel structure is also stated.The basic principle of calculating lateral displacement of adjacent bridge piles caused by excavation and unloading of foundation pit by image source method is expounded.(2)A numerical study on the influence of foundation pit excavation on the vertical displacement of existing tunnels below is carried out,the variation trend of vertical displacement and horizontal displacement of tunnel during excavation of foundation pit is also analyzed.We explore the influence of excavation space effect of foundation pit,stiffness of tunnel and supporting structure and soil reinforcement on vertical displacement of tunnel.The main research results include: with the increase of excavation width or depth of foundation pit,the peak vertical displacement of tunnel increases linearly;when the reduction coefficient of tunnel stiffness is less than 0.1,the peak value of vertical displacement of tunnel is sensitive to it;if we take the soil reinforcement to control the vertical displacement of tunnel,there is an optimum value of the length and thickness of the reinforced soil.(3)A numerical study on the influence of foundation pit excavation on lateral displacement of adjacent bridge piles is carried out,we analyze the variation of lateral displacement curve of existing bridge pile after excavation and unloading of foundation pit and study the influence of supporting structure,pile characteristics and net distance between pile foundation and foundation on lateral displacement of bridge piles.The main research results include: when the insertion ratio of diaphragm wall is less than 1.0,the lateral displacement of bridge pile is sensitive to it;before entering the bearing stratum,the lateral displacement of bridge pile increases with the increase of its length;large diameter bridge piles can reduce the peak lateral displacement,but increase the top lateral displacement;when the net distance between bridge pile and foundation pit is greater than 1.5 times the excavation depth of foundation pit,the lateral displacement of pile foundation is insensitive to it.(4)Combined with the deep foundation pit project,which close to an existing tunnel,the vertical displacement curve of tunnel after unloading of foundation pit excavation is obtained by theoretical method,we compare it with the numerical simulation results to verify the validity of the numerical model.The parameters of excavation width of foundation pit and length of reinforcement soil are analyzed,which confirms the influence of the two factors on the vertical displacement of tunnel.(5)Combined with the deep foundation pit engineering,which close to an existing bridge structure,the monitoring and analysis of the supporting axial force,the lateral displacement of diaphragm wall and the horizontal displacement of pier are carried out by using the field measurement method,we compare the monitoring data with the numerical solution to verify the validity of the numerical model;we analyze the parameters of diaphragm wall insertion ratio and bridge pile diameter,which verity the influence of the two factors on the lateral displacement of bridge piles.