三峡工程一期土石围堰设计

Design of the lst stage earth rockfill cofferdam of Three Gorges Project

三峡一期土石围堰定为4级临时建筑物，设计洪水频率为5％，相应的洪峰流量为72300m3／s。该围堰于1994年7月建成，一期基坑抽水成功，采用风化砂作为围堰的主要填筑材料，保留了部分新淤沙作堰基，用冲击及冲击反循环钻机造孔灌注柔性材料，防渗墙上接土工合成材料防渗，工程实践表明围堰设计合理，施工方便。

The first stage earth rockfill cofferdam of the Three Gorges Project was graded as a temperary class Ⅳ structure with its design flood frequence of 5% and corresponding design flood peak of 72300 m3/s. The cofferdam was completed in July 1994. The first stage foundation pit was successfully dewatered. weathered sand was used as main filling material and part of new silt was reserved as the cofferdam foundation. Percussion and reverse circulation percussion borers were adopted to make holes with flexible material poured- Compound geotextile was placed in the upper part of the cofferdam and connected with the top of the impervious wall for seepage prevention. Engineering practice has proved that the design of the cofferdam is reasonable and its construction is facile.