Influence Of Shield Construction On Underpinning Pile Foundation Of Viaducts

Metro network and viaduct network are all important measures to solve urban traffic congestion.The pile foundations of viaducts are usually more than 20 meters deep underground,and the depth of subway tunnels is usually more than ten meters underground.With the rapid development of both,therefore issues occur: the cross-interference of subways and viaducts is unavoidable.A current common solution is to underpin the viaduct pile foundation or adjust the subway line.However,due to specific requirementsin radian of the subway line and the lack of prospectiveplanning,some intersections could only be piled,then underpinned.In this paper,the R2 line of Jinan Metro is taken as a practical engineering example.Through theoretical analysis and numerical simulation calculation,the deformation of piles would be found out while dismantling the temporary pile foundation in the shield tunnel under the viaduct after replacing underpinning of viaduct.Hence,the best spacing for this process could be inferred;and the influences or issues that the shield tunneling may bring in and around Jinan,as well as the chance of deformation in local soil,and finally the modeling of the actual project.The analysis illustrated in detail that the risks exist in the project,which could contribute a great amount of information in the actual construction process.The specific conclusions are as follows:1)The theoretical basis of the effects of pile foundation underpinning and shield construction on surface deformation and pile foundation is discussed in detail.2)According to the engineering geological conditions of the R2 line of Jinan Metro and the construction of U-shields,the MIDAS software was used to establish the calculation model.The numerical simulation of the shield tunnel under-construction of the underpinning piles under the viaduct was conducted and the pile foundations with different distances were obtained.Deformation characteristics determine the best pile spacing for underpinning of viaducts,the scope of influence of shield construction on surrounding soil,and the deformation characteristics of soil.Through simulation analysis,the location of risk points was determined and used as a reference for shield construction.3)In view of the deformation problems that may be caused by the construction of tunnel shields,the deformation control measures during the pile foundation underpinning,the deformation control measures during the shield construction and the monitoring plans for the bridge structures are proposed.