Study On The Effects And Control Measures Of Adjacent Existing Single Pile Due To Shield Tunneling In Taiyuan

In recent years,with the further development of urban modernization,a large number of high-rise buildings and viaducts are located in the central area of the city.However,a majority of these buildings and structures are supported by pile foundations.So the excavation of shield tunneling adjacent to the pile foundations of existing buildings is inevitable,while the ground movements caused by excavation will inevitably lead to additional internal forces and displacements on the adjacent pile foundations,which will affect the bearing capacity and stability of pile foundation.Therefore,it is of great practical significance to study the influence of shield tunnel construction on adjacent pile foundation and its control measures.Based on the construction of shield tunnel of metro line 2 of Taiyuan,the international large finite element analytical software MIDAS-GTS was employed to build a three-dimensional model that take into account the factors such as face pressure ahead of the TBM,grouting pressure,slurry hardening time,the friction between shield and soil,stiffness transformation of shield and lining segment,pile top load.On this basis,the thesis studies the effects ofsingle-line shield tunneling and double-line shield tunneling under different excavation sequences on adjacent single pile.The results show that the horizontal displacement,moment and additional axial force of the pile are the largest near the centerline of the tunnel during the construction of single-line shield tunnel;the settlement curve of the pile is linear,and the settlement of pile top is larger than that of the pile tip,but the difference between the two is not significant;when the shield tunnel is excavated within 6 meters of the horizontal axis of the pile,the influence of the shield tunnel construction on the deformation and internal force of the pile is most significant;the influence degree of single-line shield tunneling and double-line shield tunneling under different excavation sequences on deformation and internal force of existing single pile from high to low are in the order of tunnel 1 construction before tunnel 2 construction,tunnel 2 construction before tunnel 1 construction,tunnel1 and tunnel 2 simultaneous construction,only tunnel 2 construction;during the construction of the two-way tunnel,the negative friction range on the pile is extended upwards and downwards due to the increase of the disturbance.The axial force of the pile is changed from "S" shape to "C" shape and reaches near the tunnel axis,and reached a maximum near the axis of tunnel,and the maximum axial force exceeds the pile top load.On the basis of the above,the influence of grouting pressure and face pressure ahead of the TBM on the deformation and internal force of adjacent single pile is studied when tunnel 2 is constructed before tunnel 1The resultsshow that the increase of face pressure ahead of the TBM and grouting pressure can reduce the deformation and internal force of pile within a certain range,but with the increase of face pressure ahead of the TBM and grouting pressure,the decrease rate decreases gradually;increasing the grouting pressure is more significant than increasing the face pressure ahead of the TBM in the control of pile settlement,pile axial force,horizontal displacement of the pile in X axis direction and moment of the pile in Y axis direction;increasing the grouting pressure,the degree of reduction of the displacement of the pile in the X-axis direction and the moment of the pile in Y axis direction is significantly larger than that of the pile in the Y-axis direction and the moment of the pile in X axis direction,which is opposite to the increase of the face pressure ahead of the TBM.Finally,the effect of pile length,pile diameter and pile spacing on the existing single pile is studied by orthogonal test.The results show that the isolation pile length and the isolation pile spacing have the greatest influence on the deformation and internal force of the existing single pile,and the isolation pile diameter has little effect on the deformation and internal force of the existing single pile.The influence degree of the three parameters of the isolation pile on the settlement of the pile and the additional axial force of the pile from high to low are pile length,pile spacing,pile diameter.The influence degree of the three parameters of the isolation pile on the horizontal displacement and moment of the existing single pile from high to low are pile spacing,pile length,pile diameter.