Study On The Effect Of Construction That Shield Tunnel Down-traversing The Pile Foundation Of Existing Bridge And Its Control Technology

In recent years, the great development of underground traffic makes subway lines more network and scale, the phenomenon that subway lines down-traversing the existing highway bridges is becoming more and more common. At present, there is still a lack of a mature technical specification about shield tunnel down-traversing pile foundation both at home and abroad. Although the scholars have done a massive research work on this project, the research results are not systematic and still need to carry out further study because of the complexity of shield construction technology, the traversing form, the geological condition and the limitations of the existing research level.Based on Shadi Tunnel down-traversing Fenjiang bridge engineering, this thesis researched the deformation law of formation and bridge pile foundation,s bearing behavior, mechanical characteristics, deformation properties under the influence of tunnel construction by the methods of information research, theoretical analysis and numerical simulation calculation. On this basis, this paper put forward a construction control system which is suitable for shield tunnel down-traversing the existing bridge pile foundation engineering The main results are as follows:1) This paper proved the mechanism of shield tunnel construction impact on the stratum and the existing bridge pile foundation. In the process of shield tunnel down-traversing the existing bridge pile foundation, the shield tunnel, the stratum and the existing bridge pile foundation are in an interaction system, the tunnel construction is disturbance source, deformation of stratum is medium, the existing bridge pile foundation is perturbing object. The key to control the influence of existing bridge pile foundation caused by shield tunnel construction is to limit the deformation of strata effectively.2) By establishing the model of shield construction and numerical simulation, this thesis analysed the deformation law of strata and the existing bridge pile foundation,s additional deformation and additional internal forces under the influence of the different excavation stages, the different relative position between the shield tunnel and the existing pile foundation as well as the different stratum conditions around the tunnel, then obtained the following conclusions:(1) The stratum is closer to shield tunnel, the disturbance will be stronger.(2) Pile foundation in the stratum has a shielding effect on the transfer of shield tunnel,s construction disturbance.(3) The existing pile foundation will be disturbed by the greatest degree when shield tunnel down-traversing both just below the pile foundation through or by the side through with the roof of the tunnel and the bottom of the pile at the same height; the existing pile foundation under small disturbance when the horizontal distance between the tunnel and the existing pile foundation is more than 3 times the diameter of the tunnel or the pile end is located below the shield tunnel axis.(4) With the decrease of the stratum conditions around the tunnel, the ground settlement and the additional settlement, the additional horizontal displacement and the additional bending moment of the pile foundation is on the increase.3) This paper established the shield tunnel down-traversing bridge pile foundation construction control system by select construction control measures for different objects such as the disturbance source(tunnel construction), the disturbance vector(the deformation of strata), the perturbing object(the existing bridge pile foundation).The research results of this thesis can provide guidance for design and construction of similar shield tunnel down-traversing the existing bridge pile foundation engineering, which has a certain theoretical and practical value in engineering.