二次托换技术在福州地铁紫五区间桩基托换中的应用

针对福州地铁2号线紫阳站-五里亭站盾构区间五里亭立交桥桥桩侵入隧道影响盾构掘进，且存在低净空、污水管干扰、场地狭小等施工难点问题，提出将桥梁施工工艺、钢管贝雷梁临时支撑、同步顶升、绳锯切割及全回转钻机拔桩等多项工艺有效衔接的二次体系转换法桩基托换施工技术。介绍该二次体系转换法桩基托换施工技术的施工工艺，分析其应用效果和社会经济效益。结果表明： 1）采用该桩基托换施工技术，桥梁裂缝最大为2 mm、梁底最大位移为3.9 mm、墩底最大沉降为3.8 mm、托换体系最大位移为24 mm、邻近桥墩最大沉降为1.2 mm，既有桥梁与周边环境可控。2）与常规托换梁托换后盾构破桩方法相比，工期缩短2~3个月，费用节省约50%，可克服周边复杂环境的影响，规避盾构带压开舱和破桩的风险。

Application of Secondary Underpinning Technology for Pile Foundation to Ziyang Station Wuliting Station Section on Fuzhou Metro

There are many construction difficulties for Ziyang Station Wuliting Station Shield Section on Fuzhou Metro Line No. 2, i.e. piles of Wuliting Overpass intruding into shield tunnel, low clearance, sewage pipe and small construction space. Hence, the secondary underpinning technologies for pile foundation, including bridge construction technology, temporary support by steel bailey beam, synchronous jacking, rope saw cutting and pile extraction by full circle slewing drilling machine, are put forward; and the socio economic benefits are analyzed. The study results show that: (1) By using the secondary underpinning technology for pile foundation, the maximum displacements of bridge crack, beam bottom, pounding bottom, underpinning system and point close to piers are 2 mm, 3.9 mm, 3.8 mm, 24 mm and 1.2 mm respectively; and the existing bridge and surrounding environment can be controlled. (2) Compared with traditional shield cutting piles after pile foundation underpinning method, the construction period and cost can be reduced by 2 to 3 months and 50% respectively by using the secondary underpinning technology for pile foundation; the adverse effects induced by surrounding complex environment can be overcome, and the risk of hyperbaric operation and cutting piles of shield can be avoided.