深水基础超长钢板桩围堰设计与施工关键技术

芒稻河特大桥主桥为(77+3×130+82)m预应力混凝土刚构-连续梁组合体系桥,主墩基础位于深水区,承台施工时抽水最大水头达18.7m。采用钢板桩围堰施工承台,围堰最大平面尺寸为45.6m×16.8m,采用拉森Ⅳw型钢板桩,单根桩长36m,围堰内设置5道内支撑。采用有限元软件,计算围堰3个主要施工工况下钢板桩和内支撑的变形、应力,以及围堰封底抽水完成工况下封底混凝土的抗浮安全系数和应力,计算结果均满足要求。施工时,采用定位导向架和平面定位框限位插打钢板桩,内支撑采用工厂拼装现场分层整体吊装、水下抄垫等工艺,应用水下分阶段吸泥、水下二次封底等施工技术,实现了深水钢板桩围堰快速安全施工。

Design of Very Long Steel Sheet Pile Cofferdam for Deep Water Foundation and Key Construction Techniques

The main bridge of Mangdaohe River Bridge is a prestressed concrete rigid frame-continuous beam composite system,with span distribution of 77,3×130,and 82 m.The foundations of main piers are located in deep water area,during the construction of pile caps,the maximum pumping head reaches up to 18.7 m.The steel sheet pile cofferdam,with maximum plan dimension of 45.6 m×16.8 m,is utilized for pile cap construction.The cofferdam is formed of IVw type steel sheet piles of 36 m long each,inside which five inner bracings are installed.The finite element software was used to calculate the deformation,stresses of the steel sheet piles and inner bracings under the three major loading conditions as well as buoyancy factor and stresses of the base sealing concrete when the base sealing and water pumping work for the cofferdam was finished.The calculated data meet the requirements.In the construction process,the positioning and guiding frames and the frames for plan positioning were deployed for position-limiting and driving of the steel sheet piles.The inner bracings were assembled in the factory,integrally hoisted and installed layer by layer at the bridge site.A series of construction techniques were employed to realize the rapid and safe construction of the deep-water steel sheet pile cofferdam,like using underwater pads,dredging slurry stage by stage and sealing the cofferdam by two times.