三峡工程一期土石围堰的施工及运行要点

三峡工程一期土石围堰全长约2500m，高度30～40m，束窄原河床约30％。围堰施工的主要难点是：工期紧、强度高，石渣、块石料缺乏，迎水侧水下清基与堰体填筑干扰大，防渗墙施工困难。针对这些难点采取了如下一些对策：试验段提前施工，开辟过渡性料场，优化水下填筑程序，在防渗墙造孔中钻爆结合对付块球体，用湿磨细水泥灌浆帷幕部分取代防渗墙，部分采用高压旋喷防渗等10项措施。为了确保安全和为二期深水围堰的建造积累经验，对一期围堰进行了多项监测。监测结果表明，运行近一年中，围堰工作状态正常，渗漏量仅200L／min。

Construction of Three Gorges Project's 1st stage earth and rockfill cofferdam and its operating points

The 1st stage earth and rockfill cofferdam of Three Gorges Project has a total length of some 2500m, with its height of 30~40m and reduced river width of some 30% original one. The major difficulties of constructing the cofferdam are: very short construction time, high working intensity, shortage of block stone, much interference of water side foundation stripping and of cofferdam body filling, and difficult construction of seepage-proof wall. In order to overcome these difficulties, were taken the following measures: early construction of the cofferdam's experimental section, mining of the transitory quarries, optimization of under water filling procedure, combination of blasting and drilling for holemforming of the seepage-proof wall, using the grout curtain of wet-ground cement partially instead of the seepage-proof wall, and partially adopting high pressure jet grouting for seepage-proof, etc. To ensure the safety of 1st stage cofferdam and accumulate experience for constructing 2nd stage deep water cofferdam, a number of monitoring items were conducted on 1st stage cofferdam. The monitoring results show that approximate one year after operation, the behaviour of the cofferdam is normal, with the seepage discharge of 200 l/min only.