深水漂卵石地层桥梁承台锁口钢管桩围堰设计与施工研究

Study on Design and Construction of Steel Pipe Pile Cofferdam with Lock Mouth on Bridge Pile Cap in Deep Water Boulder and Pebble Stratum

某铁路连续梁桥主墩3号墩位于安宁河中,承台施工期水深6 m,墩位处地质主要为大粒径的漂卵石和松散卵石土,部分位置有风化岩石;承台埋置深,需要在水下开挖的基坑深度达8 m,采用了CT锁口钢管桩围堰作承台施工的围护结构。基于承台处于大块漂卵石地质或风化岩石地层,采取了先钻孔后以砂土置换卵石土层再插打锁口钢管桩工法,保证了钢管桩打入深度足够、姿态顺直,且锁口部位变形小。经现场锁口止水材料配合比设计及工艺模拟试验,选取了适宜的锁口止水材料和填充工艺,经围堰施工完成抽水后验证,锁口止水效果良好。

The No.3 main pier of a railway continuous beam bridge is located in the middle of Anning River. During the construction period of the pile cap, the water depth is 6 m. The geology of the pier is mainly composed of large grain size boulders and pebbles and loose pebble soil, some of which are weathered rocks. The buried depth of the cap is deep and the depth of the foundation pit needs to be dug under water is up to 8 m. CT lock-mouth steel pipe pile cofferdam is adopted as the enclosure structure for the cap construction. Based on the fact that the pile cap is located in the geology of large boulders and pebbles or weathered rock stratum, the method of drilling and replacing the pebble soil layer with sand soil followed by driving the steel pipe pile with lock mouth is adopted to ensure that the steel pipe pile is driven deep enough, straight and with small deformation at the lock mouth. The suitable water sealing material and filling technology of lock mouth are selected through the design of mix proportion of lock mouth water sealing material and process simulation test. After the cofferdam construction is completed and pumping, it is verified that the lock mouth is effective in water sealing.