Passive Bridge Pile Foundation Underpinning Scheme Research And Application

As cities develop toward large and modern ones, the traffic pressure on the ground becomes more and more serious. In order to alleviate the ground traffic pressure, the underground railways, effective and convenient, become the preferred choice of those big cities for alleviating traffic problems. Besides, the development level of underground railways is becoming an important index for appraising the modernization of a city. The building of underground railways inevitably conflicts with the existed building foundation. Therefore, pile foundation underpinning is needed in a tunnel. Pile foundation underpinning is inseparable with the construction of tunnel, so in tunnel construction, the study of mechanical behavior in pile foundation underpinning has practical significance.This paper firstly introduces some classifications of pile foundation underpinning, the main types and features of underpinning pile and the main types of underpinning bearing systems. Then this paper explains the research status of pile foundation underpinning at home and abroad, some important examples, and several points that need attention in the underpinning process.The design theory of pile foundation underpinning is elaborated. Especially, the important and difficult points of structure design in pile foundation underpinning are concluded and the design methods of every part in underpinning structures are also given. The design thinking of the nodes between the underpinning beam and the new underpinning pile, the anti-shear mechanism of the node between the underpinning beam and the pile and the construction monitoring systems of pile foundation underpinning are all explained in detail.The tunnel construction situations of Lanzhou Line 1 subway, from Gongxingdun to Jiaojiawan, which goes through Lannigou bridge, are introduced and also the related theories of finite elements in data analysis. The digging of the tunnel going through Lannigou bridge and the process of cutting piles are numerically modeled, and the mechanical behaviors of pile foundation and soil layer are analyzed. The structural subsidence caused by bridge doesn’t meet the requirements from the analysis of controlling subsidence, so the bridge must be reinforced and improved.Three feasible schemes are put forward for reinforcing and improving the bridge through the Lannigou bridge. Finally, the method of comparative analysis is adopted and it is proved that the passive pile foundation underpinning is the preferred scheme. The passive pile foundation underpinning process, pile foundation underpinning on the ground and pile cutting in the tunnel, is numerically modeled in detail. This scheme is proved rational and feasible from the calculation results analysis of subsidence, stress and internal stress.