深水无覆盖层超倾斜岩面河床桥塔基础施工技术

Construction Technique for Pylon Foundation in Deepwater Over-Inclined Bedrock without Overburden

安徽省望东长江公路大桥主桥为(78+228+638+228+78)m的组合梁斜拉桥,南桥塔基础范围无覆盖层,河床岩面倾斜高差达10.22m。综合考虑南塔处地质水文情况,基础采用先施工钢围堰,后搭设钻孔钢平台的施工方案。根据河床基岩面变化,钢围堰底口设置成高低刃脚。在工厂进行钢围堰卧式拼装,在围堰顶口和底口焊接临时挡水板,使围堰形式类似船体结构,卧式浮运到桥塔附近水域,对围堰进行竖向转体并定位下沉,安装桩基钢护筒,钢围堰封底并锚固钢护筒,利用钢护筒搭设钻孔平台进行桩基施工,钢围堰抽水后进行承台施工。

The main bridge of the Wangdong Changjiang River Highway Bridge in Anhui Prov- ince is a composite girder cable-stayed bridge with span arrangement of （78＋228＋638@228@78） m. No overburden is found where the south pylon foundation is located, the sloping elevation difference of the bedrock surface is up to 10.22 m. By considering the geological and hydrological condition at the south pylon, the foundation was constructed by the scheme of constructing the steel cofferdam first and the steel platform for hole boring later. The bottom of the steel cofferdam was designed to have cutting edges with different depths so as to suit the variation of the bedrock surface. In the workshop, the steel cofferdam was put to lie down, to the top and the bottom of which temporary water-retaining plates were welded to make the cofferdam be a structure similar to a boat. Then, the cofferdam was floated to the region near the bridge pylon, vertically rotated and positioned, and sank into place. Further, the steel casings for the foundation were driven, the bottom of the steel cofferdam was sealed and the steel casings were anchored. The steel casings were used for the installation of the hole boring platform in the pile foundation construction. After the water in the steel cofferdam was pumped out, the construction of the pile caps began.