深水浅覆盖层倾斜岩面河床围堰设计及应用

Design and Application of Cofferdam for Riverbed with Inclined Rock Surface in Deep Water and Shallow Overburden

在浅覆盖层、倾斜岩面河床区域通常采用双壁钢围堰方案,因受限于钢管桩难以插打入岩层,较少采用锁扣钢管桩围堰方案。以合安高速公路渠江特大桥2号墩基础施工为例,针对其深水、浅覆盖层、倾斜岩面河床的特点,从方案比选、围堰设计、应用实践等方面进行了深入研究。该项目最终采用嵌岩式锁扣钢管桩围堰方案;通过冲击钻提前引孔,将钢管桩端部嵌入基岩,再进行钢筋混凝土桩锚固,并对桩端锚固方式进行预备方案设计;钢管桩锁扣处采用灌入中粗砂法进行止水,与注入胶凝材料相比,提高了钢管桩回收率。通过现场实施效果可以看出,在深水浅覆盖层倾斜岩面河床条件下,设计采用嵌岩式锁口钢管桩围堰方案是成功的,可以有效减少施工难度、大幅度降低成本、缩短施工工期。

Double-wall steel cofferdam is usually used in shallow overburden and inclined rock riverbed areas.Because it is difficult for steel pipe piles to be inserted into rock strata,locking steel pipe pile cofferdam is rarely used.Taking the foundation construction of No.2 pier of a super-large bridge spanning Qujiang River on Hefei-Anqing Expressway as an example,this paper made an in-depth study from the aspects of scheme comparison,cofferdam design and application practice according to the characteristics of deep water,shallow overburden and inclined rock riverbed.The project finally adopted the scheme of rock-socketed locking steel pipe pile cofferdam;the end of steel pipe pile was embedded into the bedrock by percussion drilling in advance,and then the reinforced concrete pile was anchored,and the preparatory scheme design of pile end anchorage mode was carried out;the lock of steel pipe pile adopted the method of pouring medium coarse sand to stop water,which improved the recovery rate of steel pipe pile compared with the injection of cementitious material.Through the field implementation effect,it can be seen that under the condition of inclined rock riverbed in deep water and shallow overburden,the design of rock-socketed steel pipe pile cofferdam scheme is successful,which can effectively reduce the construction difficulty,greatly reduce the cost and shorten the construction period.