洞内大轴力大跨径拱式桩基托换在地铁建设中的研究与应用

广州地铁某新线区间矿山法隧道，因线站位设置需近距离下穿某大型地下空间，与其5根既有桩基冲突，需要进行托换。受各制约因素影响，工程采用洞内拱式托换方案，然而本次托换的桩轴力、隧道跨径和现场条件的复杂程度，均远超一般洞内托换。以洞内大轴力大跨径拱式桩基托换为研究对象，通过工程类比的方法总结出托换结构断面高宽与托换跨径和桩轴力之间的经验关系（尺寸初拟规律），并进一步通过2D荷载结构法进行内力分析和3D地层结构法进行变形模拟，对托换结构的承载力和正常使用极限状态进行验证，证明了洞内拱式托换可适用于大轴力大跨径情况，验证了托换结构尺寸初拟规律的可应用性。

Research and Application of Arch shaped Pile Foundation Underpinning in Tunnel with Large Axial Force and Span of Metro Construction

Due to alignment requirement, a mined tunnel section of a new line of Guangzhou Metro should closely cross underneath a large underground commercial space. There are 5 pile foundations should be underpinned. As a result, the in tunnel arch shaped pile foundation underpinning scheme is adopted for various restraining factors such as large pile axial force, large tunnel span and complex field conditions. The empirical relationship between the height and width of underpinning structure cross section and tunnel span and pile foundation axial force is revealed by engineering comparison; moreover, the structural internal force is analyzed by 2D load structure method and the deformation is simulated by 3D stratum structure method, so as to verify the bearing capacity and normal service limit state of the underpinning structure. The results show that the in tunnel arch shaped pile foundation underpinning scheme is feasible in case of large pile loads and tunnel span, and the preliminary rules for the dimensions of the underpinning structure are applicable.