The Study On The Impact Of Metro Shield Tunneling Crossing Through Bridges On Surrounding Engineering Environment

With the continuous construction of subway in China,engineering and technical problems are constantly changing and upgrading.Because the distribution of underground space was seldom considered in the early urban construction,it was inevitable that the existing pile foundation would intrude into the tunnel in the design process of shield tunnel.In the process of subway construction,the method of pile foundation underpinning will be considered to solve the problem,and the old piles will be directly removed by shield.However,both pile underpinning and shield cutting pile will have a great impact on the surrounding engineering environment,which will lead to the damage of the pile foundation of the construction structures and cause engineering accidents.According to the influence of Nanchang Metro Line 2 shield under Bayi Bridge on the surrounding engineering environment,the main research contents are as follows:Pile underpinning is needed in some sections of Nanchang Metro Line 2 due to some single columns and single piles intruded into the tunnel by Bayi Bridge.And pile underpinning will have a greater impact on the surrounding engineering environment.In this paper,one of the pile foundations was used to simulate the three key steps of underpinning construction: jacking,unloading and pile cutting with the finite element software ABAQUS,and the monitoring results of the three construction stages were analyzed.The results show that the displacement changes of bridge pier,underpinning beam and new piles are all within the safe range,and the construction scheme can effectively control the deformation.However,the monitoring of new piles and bridge piers should be strengthened in the jacking and pile cutting stages.After underpinning the original single-column and single-pile bridge,the following two situations will occur: the distance between the new underpinning piles and the tunnel is different,and the angle between the underpinning beam and the tunnel is different.In this paper,the influence on the surrounding engineering environment when the subway shield tunnel passes through the new underpinning piles at different positions is studied according to the ratio of 1:30 through the physical model test.The results show that when the angle between underpinning beam and tunnel is constant,the smaller pile distance is,the greater influence on pile foundation is.When the pile distance is constant,the smaller included angle between underpinning beam and tunnel,the greater influence on pile foundation.Special attention should be paid to the design of underpinning piles with small pile spacing and small angle.In practical engineering,subway shield often chooses the appropriate buried depth according to the surrounding engineering environment.This paper used the method of combining physical model test and numerical simulation to study the influence of ground surface settlement and internal force of underpinning pile when the buried depth of subway shield tunnel is different.The results show that the deeper tunnel is buried,the smaller impact on the ground surface settlement,but the greater impact on the piles.In addition,the location of the tunnel has the greatest impact on the pile body.In the design of underpinning piles,the pile body in the tunnel area should be strengthened.In order to further study the influence of slurry shield and old pile cutting on pile foundation,this paper used the finite element software ABAQUS to simulate the site construction,and focuses on the analysis of the variation law of the horizontal bearing characteristics of underpinning piles.The research results show that the removal of old pile will lead to large bending moment,shear force and horizontal displacement of underpinning piles,so the monitoring of surrounding engineering environment should be strengthened in the actual engineering.