珠海洪鹤大桥8号主墩基础施工关键技术

Key Construction Techniques for Main Pier No.8 Foundation of Honghe Bridge in Zhuhai

珠海洪鹤大桥主桥由2座主跨均为500 m的双塔双索面结合梁斜拉桥串联而成,其中8号主墩位于海岸浅滩区,墩位处淤泥层厚8.8~37 m,覆盖层平均厚48 m,岩层埋深较深,且呈斜面发育,岩石强度高达100 MPa。8号主墩承台尺寸为42.1 m×22.6 m×6.5 m,采用∅2.8 m钻孔灌注桩群桩基础,采用先平台后围堰工序施工。钻孔平台采用土工布砂袋围堰筑岛施工技术,解决了深淤泥地质中筑岛施工容易出现的滑移和沉降;钻孔桩采用“旋挖钻+回旋钻”组合成孔技术进行钻孔深度超100 m的超深大直径嵌岩桩施工,充分发挥2种钻机在不同地质和钻孔深度的优势,极大提高了成孔效率;承台深基坑围堰采用“大型钢板桩围堰+干挖法”施工技术,有效减少了深基坑围堰施工中围堰的变形失稳和沉降。

The main bridge of Honghe Bridge in Zhuhai features the two composite girder cable-stayed bridges that are arranged in tandem.Each cable-stayed bridge has two pylons creating a main span of 500 m,and the stay cables are laid out in double cable planes.The main pier No.8 is located in the coastal shoal area,where the silt thickness is about 8.8 m to 37 m,the overburden thickness reaches 48 m,the bedrock is deeply buried,with deep slopes,and the rock strength exceeds 100 MPa.The pile cap of the main pier No.8 measures 42.1 m by 22.6 m by 6.5 m,which is mounted on the foundation of 2.8 m-diameter bored piles,and constructed with the support of a cofferdam.To facilitate the installation of the boring platform,an artificial island was built using the geotextile sandbags cofferdam to prevent the occurrence of collapse and settlement of the artificial island in the deep silt soil.To construct the large-diameter rock-socketed piles that exceed 100 m in length,the boreholes were made by the combined utilization of rotary drilling rigs and auger drilling rigs,to make the most of the advantages of the two types of rigs to address the geological condition and borehole depths,and in turn to improve the borehole formation efficiency.The deep-foundation-pit cofferdam is a large-scale steel sheet pile cofferdam,and the foundation pit was excavated by dry excavation method to effectively reduce the cofferdam deformation and settlement during construction.