裸岩河床水中墩基础施工技术

Construction Technique for River Pier Foundations Sitting on Bare Rock Riverbed

长昆客专罗旧舞水特大桥主桥为（48＋2×80＋48）m连续梁桥,1号~3号桥墩位于主河槽内,低桩承台嵌入河床裸岩中,设16根1.5m钻孔桩。根据裸岩河床、低桩承台的特点,确定水中墩基础施工采用施工栈桥为交通便道、施工平台,栈桥标准跨度18m,设4组贝雷梁、双排钢管桩基础,并在钢管桩周围抛填砂砾、投放石笼或下放钢套箱、灌注水下混凝土以及拉设缆风绳。水中墩基础采用矩形双壁钢围堰围护方案,按照＂先堰后桩＂顺序施工。水中墩基础施工中,采用长臂挖机清底,利用岩石乳化炸药和非电微差雷管进行水下岩石爆破;钢护筒采用振动锤夹持、插打;双壁钢围堰依靠钻孔桩护筒、平台辅助钢管桩逐块拼装,用倒链下放、汽车吊接高下沉施工;围堰封底混凝土等强后,进行钻孔桩、承台和墩柱施工,最后拆除围堰。

The main bridge of Luojiu Wushui River Bridge on the Changsha-Kunming Passenger Dedicated Railway is a（48＋2×80＋48）m continuous beam bridge.The pier No.1,pier No.2 and pier No.3 stand in the main river channel,the low pile caps of which are embedded in the bare rocks on the riverbed.The foundation of the pier consists of 16 bored piles each 1.5m in diameter.To suit the characteristics of the bare rock riverbed and the low pile caps,the construction trestle was used as the transportation access and the construction platform during the construction of the river pier foundations.The trestle,with standard span length of 18 m,consists of 4 groups of bailey beams that are supported by two rows of steel pipe piles.The steel pipe piles were surrounded by riprap,based on which the stone cage or suspended steel box was lowered.Then the tremie concrete was cast and wind cables were installed and tensioned.The river pier foundation was constructed with the assistance of the rectangular double-wall steel cofferdam,following the sequence of constructing the cofferdam first and then the piles.During the construction of the river pier foundation,the long boom excavator was used to clean the base,and the rock emulsified explosive and the non-electric split-second delay detonators were used to blast the underwater rocks.The steel casing was held and driven by the vibratory pile hammers.The double-wall steel cofferdam was assembled block by block with the assistance of the steel casings of the bored piles and steel pipe piles supported platform,and lowered using the chain blocks and extended lift by lift and submerged by using the truck crane.After the base sealing concrete in the cofferdam was hardened,the construction of the bored piles,pile caps and pier shafts were carried out.And the final work was to dismantle the cofferdam.