The Application Of Passive Pile Foundation Underpinning Project To Subway Construction

With the fast development of economy,China’s rail transportation develops quicklythroughout the whole country. Due to subway construction is an important solution to solveurban public traffic problems, it will inevitably produce a conflict between the undergroundrailway lines and the existing buildings underground foundation. When having subwayconstruction in the center area of city, lines will actually avoid large,high-rise buildings, whilethe low layer buildings are always be ignored. Since underpinning become an very importantmethod in rail construction, researching to the mechanical behavior of underpinning becomesindispensable.Firstly,the paper mainly introduce the origin and the development of pile foundationunderpinning project. Combine the application examples of subway tunnel engineering at homeand abroad, the paper also introduce the craft and characteristics of raft foundation underpinningproject、 root pile foundation underpinning project、 initiative foundation underpinningproject．Secondly, the paper focus on the craft of passive pile foundation underpinning project,the method of establishing mechanical model and simplified calculation. Based on theGuangzhou metro Line Six which across the pile foundation of Guangdong Shipping Board’sdormitory in Yuexiu District, the paper introduce the design and construction programs, andthen calculate the settlement with the simplified mechanical model. Compared with themeasured values, the results showed that the simplified mechanical model is too conservativeand it can be optimized.Thirdly, the author re-establish the working conditions model of pile foundationunderpinning project and proposed that the orgin pile have remanent strength after cut off. Theunderpinning pile can be seen as the elastic support of underpinning beam. With thedeformation,the underpinning system achieve the stress re-distribution. the value of deformationdepends on the stiffness of underpinning beam, when the elastic support is added to theunderpinning system, the underpinning stiffness can be greatly increased and verticaldeformation value can be reduced. And this is the working principle of underpinning system.With the principle， the author can re-establish the mechanical model which consider theremanent strength.And then, the author introduce the basic principle of finite element method and3D finiteelement software. With analyzing the mechanical model which consider the remanent strength, the paper have a comparison about the situation between underpinning way andnon-underpinning way. Compared with the measured values, the results showed that the analysisresults of3D finite element is closing to the measured values.It means that the mechanical modelis representative.With the results of the two calculation methods and the the actual situation,the author provethat the deformation can be controlled in allowable range when the passive pile foundationunderpinning project was used to reduce the deformation of a8-story frame structure building.At last, we can draw a conclusion that the passive pile foundation underpinning project isfeasible and reasonable when applying in a8-story frame structure building.