The Entire Numerical Analysis Of Expanding Foundation Of Highway Bridge With Under- Ground Shield Tunneling On Rock

With the development of the city,three-dimensional traffic emerges during the construction,and the problem of intersecting of bridges and tunnels is inevitable.Tunnel construction causes displacement and deformation on the surface,affecting the existing bridges.It is of great practical significance to study the effect of tunnel construction on the existing expanding foundations of rock and to evaluate the safety of these bridges to ensure the normal use and operation of bridges.This paper aims at the existing expanding foundations on rock,establishing finite element models,and simulating the influence of the whole process of excavating tunnels to the expanding foundations of bridges.At the same time,for the construction of tunnels,different influencing factors are controlled and analyzed to obtain the influence of different factors on the expanding foundation.The main research contents of this paper are:(1)The theoretical principles of settlement caused by the construction of tunnels are analyzed and discussed.The related concepts such as the Peck formula are explained.Specifically,after the construction of tunnels,law of change of the sectional,longitudinal and horizontal displacements of the surface were discussed.(2)The different damage modes of bridge foundation in tunnel construction are explained.There are five main effect aspects to the expanding foundation of bridge: the settlement of the surface,horizontal displacement,inclination,curvature,and horizontal deformation;and the evaluation criteria is discussed in terms of damage model of the bridge foundation.(3)The constitutive models of rock foundation and concrete materials are selected,establish an entire finite element model and analyze the basic forms of the basement reaction and shear stress on the rock foundation.The base reaction force basically shows that the center of the pier has a large force,and reaction force gradually decreases to the two sides but increase at the edge;the shear stress distribution remains zero in the center of the pier and the center of the basic set,and it keeps increasing and then decreases when it diffuses to the two sides,but increase at the edge.(4)Establish the entire finite element model of tunnel-foundation-bridge-bridge foundation,simulate the whole process of tunnel construction,and analyze the effect of the whole process of the construction to the expanding foundations of different parts of the bridge.The law of settlement,base reaction force,and shear stress of the expanding foundation of the bridge during the tunnel construction are discussed.The different parts of the expanding foundation are compared with each other,and sum up the laws and analyze the causes.It is considered that the settlement of the tunnels process can be divided into 5 stages,and not all of them are settlements but uplifts.After construction,the basement reaction force of edges are reduced,and the shear stress changes to increase from the center of the foundation to the pier and decrease from the pier to the edges.The zero point of shear stress at the pier moves toward the base edges.(5)Establish a part finite element model of tunnel-foundation-expanding foundation and analyze the influence of different factors on the expanding foundation of the existing bridge.The changes of the depth of the tunnel,the horizontal distance between the centerline of the tunnel and the center of the expanding foundation,the stiffness of the foundation,the span-height ratio of the foundation,and the water level are analyzed.The impacts of settlement,basement reaction force,and shear stress of the expanding foundation of the bridge are summarized qualitatively,the trends of change and the reasons are analyzed.It is concluded that the influence of tunnel depth and horizontal distance to spreading foundation on the foundation settlement is basically in accordance with the Peck formula.The increase of foundation stiffness will reduce the settlement of spreading foundation after tunnel excavation.The larger the span-height ratio of the foundation,the more obvious the uneven settlement.The change of the buried depth and horizontal position of the tunnel has little effect on the expansion of the basement reaction force.Relatively speaking,the stiffness of the foundation,the span-height ratio of the foundation and the change of the water level have a great influence on it.As the foundation stiffness decreases and the span-height ratio of the foundation increases,the shear stress of the expanding foundation increases accordingly.