平潭海峡公铁两用大桥深水区围堰施工关键技术

平潭海峡公铁两用大桥深水区非通航孔引桥为跨径80(88)m的简支钢桁梁桥,采用钻孔桩基础,承台基础采用钢吊箱围堰施工。钢吊箱围堰尺寸为32.0m×19.8m×20.4m,承台顶面以下围堰为双壁结构,壁厚1.0m,内设2层内支撑,封底混凝土厚3.5m。考虑到平潭海峡浪高、风大、流急、潮差大等影响因素,围堰完成封底、抽水后,安装抗浮牛腿,以满足围堰的整体抗浮、抗沉要求;围堰在工厂内分块加工、拼装,侧板与底板间采用螺栓连接,以实现围堰的快速安装和倒用;在围堰内设置了3层限位装置,以解决波浪力和水流力引起的围堰下放精度难以控制的问题;在围堰侧板与底龙骨间采用螺栓连接,以满足围堰的防浪、防渗要求。

Key Techniques for Construction of Cofferdam in Deep Water Area for Pingtan Straits Rail-cum-Road Bridge

The non-navigable span approach bridge of the Pingtan Strait Rail-cum-Road Bridge over the deep water is a simply supported steel truss bridge with a span of 80 (88) m. The piers of the bridge are made of bored pile foundation which is constructed with steel boxed cofferdam. The structure of the steel boxed cofferdam has the dimensions of 32.0 m×19.8 m× 20.4 m. The cofferdam below the top surface of the cap has a double-wall structure with a wall thickness of 1.0 m, two layers of internal support, and a bottom concrete thickness of 3.5 m. The influences of wave height, strong wind, flow hurry and tidal range in Pingtan Strait are taken into account, therefore, after the cofferdam is sealed and pumped, an anti-floating bracket is installed to meet the requirements of overall anti-floating and anti-sinking of the cofferdam. The cofferdam is manufactured and assembled in pieces in a factory. Bolts are used to connect the side plate and the bottom plate to realize the quick installation and reverse use of the cofferdam. At the same time, 3-layer guiding and limiting devices are also arranged to solve the problem of the low accuracy caused by wave force and flow force when the cofferdam is lowered into the water. Bolt connection is adopted between the side plate and bottom keel of cofferdam to meet the requirements of wave and seepage prevention.