地铁车站超宽深基坑内既有高架桥梁桩基托换关键技术研究

佛山地铁2号线换乘车站张槎站基坑宽50.3 m，深16.9 m，局部位于既有禅西大道桥下（净高仅7 m）。为解决低矮空间下超宽深基坑支护、既有高架桥桩基托换等难题，提出如下技术措施： 1)采用高桩承台桩基托换技术对位于车站中央桥桩进行托换，托换承台高于车站基坑面，基坑内支撑穿过新旧桩基形成对撑，内支撑与新旧桩相对独立； 2)地下连续墙幅宽调整为4 m，采用小型钻机成槽，以改善桥下施工工艺； 3)地下连续墙与两侧既有桩之间增加防塌孔措施； 4)基坑内支撑均采用混凝土支撑并加临时立柱以增加内支撑稳定性。以上措施解决了托换体系与车站基坑相互影响的问题，确保了低矮空间下超宽深基坑施工安全及既有桩基的安全。经数值计算论证、现场施工验证，提出的超宽深基坑内既有高架桥梁桩基托换关键技术是合理、安全、可行的。

Key Underpinning Technology for Pile Foundation of Existing Viaduct Beam in Super wide Deep Foundation Pit of Metro Station

The width and depth of the foundation pit of Zhangcha Station on Foshan Metro Line No. 2 are 50.3 m and 16.9 m respectively. Part of the pit is located under the existing Chanxi Road Bridge with clear height of 7 m. In order to solve the problems of support of super wide deep foundation pit in low space, pile foundation underpinning of existing viaduct, etc., a series of technical measures are proposed, as follows. (1) Pile foundation underpinning of high rise pile cap technology is used to underpin the bridge pile in the middle station, and the underpinning cap is higher than the surface of station pit; the inner support of the foundation pit passes through the existing and new pile foundation to form a symmetrical support; and the inner support is relatively independent of the existing and new piles. (2) The width of the diaphragm wall is adjusted to 4 m; and the small drilling rig is used to cut the groove to improve the construction technology under the bridge. (3) The measures of increasing the anti collapse hole between the diaphragm wall and the existing piles on both sides is proposed. (4) The inner support of foundation pit adopts concrete support and temporary columns to increase the stability of inner support. The measures adopted have solved the mutual influence of underpinning system and foundation pit, which can ensure the safety of super wide and deep foundation pit in low space and the safety of the existing pile foundation. The numerical calculation and field construction indicate that the key underpinning technology for pile foundation of existing viaduct in super wide and deep foundation pit is rational, safe and feasible.