| In recent years,subway line construction is becoming more and more common with the rapid development of urban economy,and major cities in China have begun large-scale subway construction.The shield tunneling technology is mainly used in subway construction at present.The shield diving method has the advantages of safe excavation and fast tunneling speed.However,there are often subway lines crossing between underground piles of bridges in the construction of subway by shield tunneling technology,which will cause ground displacement and affect the settlement of bridge pile foundation and the superstructure nearby.Therefore,it is of great practical significance to study the influence of shield tunneling construction on the bridge pile foundation nearby.Based on the Shihu Bridge project of Guangzhou Rail Line 14 tunneling under the North Second Ring Highway,this paper summarizes the existing theoretical research combined with the actual characteristics of the soil layer of the project and analyzes the influence of shield driving on the pile foundation of nearby bridges by using the finite element software Midas/GTS.The main contents are as follows.(1)The influence of shield tunneling construction on the pile foundation of nearby bridges and the corresponding solutions are expounded.Additionally,the impact mechanism of tunnel construction on nearby bridge pile foundation is proved.(2)Finite element software is used to carry out numerical simulation of the process of shield tunneling construction and analyze the influence of different construction stages on the nearby bridge pile foundation.According to the characteristics of construction,four kinds of analysis of working condition are determined in this paper: before the cutter head of shield machine reaches the bridge pile foundation;the cutter head and pile are in the same cross section;after the shield body passes,the gap is not filled before;after the shield body passes,the gap is filled with ordinary cement mortar.Midas/GTS were used to analyze the stress of the shield machine itself,the stress and the deformation of nearby bridge foundation and the settlement of the bridge surface under these four working conditions.Based on the analysis results,the following conclusions are obtained:(1)When shield tunnel passes through the side of the pile foundation,the pile foundation displacement and ground subsidence induced by the whole process do not exceed the specified value,meeting the requirements.(2)When shield tunnel passes through the side of the pile foundation,the maximum displacement response of the pile foundation is horizontal displacement,and the vertical displacement is relatively small.The horizontal displacement of the pile foundation should be monitored emphatically,especially when the cutter head of the shield machine is about to reach the pile foundation and the displacement increment is larger at this time.(3)The greater the pressure of tunnel face is,the greater the horizontal displacement response of pile foundation will be,and the influence of the pressure of heading face on the vertical displacement of pile foundation can be almost neglected.(4)For the purpose of stabilizing the soil in front of the shield tunneling under the engineering geologic requirement,the heading face pressure can be applied,but the heading face pressure should not exceed 0.2 MPa.(5)When the tunnel is in a relatively deep burial depth,the pressure of the tunnel face has little effect on the uplift of the surface.(3)Difference analysis is made on pile foundation displacement,ground subsidence and internal force of tunnel segment in the process of lateral crossing the bridge foundation of double track tunnel successively.The following conclusions are obtained:(1)The construction sequence of double-track tunnel has little effect on the ultimate induced displacement response of pile foundation,but has great influence on the vertical displacement induced by construction.After the excavation of the right line,the vertical displacement of the pile foundation is 3 times that of the two left line excavation.(2)The sequence of double line construction has nearly no effect on ground settlement and internal force of tunnel segments. |
PDF Full Text Request