水中长大钻孔桩施工技术

南京长江隧道右汊大桥为独塔自锚式悬索桥，主塔基础采用钻孔灌注桩基础，为14φ2．5m钻孔灌注桩，柱桩设计，桩长87m，桩身进入粉细沙层及弱风化粉砂质泥岩等复杂地质，入岩深度均不小于38m。针对这种水中、复杂地质条件下、大直径、入岩深钻孔桩，采用水中钢平台、气举反循环钻机钻孔施工，圆满地完成了钻孔桩施工任务，为此类超大型钻孔桩施工积累了经验。

Construction Technology for Underwater Long and Large Bored Piles

The fight-branching bridge in Nanjing Yangtze River Tunnel, which is a self-anchored suspension bridge with single tower, adopted bored piles foundation as its main tower＇s basis, with 14φ2.5 m bored piles and the designed 87 m columnar piles. The piles go deep into the powder sand layer and weakly weathered silty mudstone and other complex geology, and the depth into rock is all not less than 38 meters. With regard to these underwater and large-diameter bored piles which are under complicated geological conditions and deep into the rock, the underwater steel platform and air-lift reverse circulation drilling rig construction were applied and the construction task of bored piles were successfully completed, which provided a reference for the construction of such mega bored piles.