三峡工程二期围堰运行后的性状调查和试验

Investigation on Removal of Stage Ⅱ Cofferdam of Three Gorges Project

在三峡工程二期深水高土石围堰拆除过程中,对堰体和防渗墙进行了调查、取样和相关参数的测试,在此基础上,就人们关注的一些技术问题进行了分析和讨论,获得了如下认识:①风化砂堰体的密度有所增大,增幅约30%;②防渗墙墙体材料的抗压强度和初始切线模量均有一定程度的增长,模强比基本不变,渗透系数也有降低趋势;③防渗墙各槽段之间存在套接缝,缝宽2～3mm,抗渗透破坏性能良好,但它是防渗墙中抗渗透破坏的薄弱部位;④防渗墙和风化砂之间普遍存在薄膜型泥皮,厚度在2～3cm之间,风化砂—泥皮—防渗墙之间分界明显;⑤防渗墙顶部所接土工膜整体完整性较好,土工膜之间的搭接良好,但土工膜与防渗墙顶部混凝土搭接处,局部有不同程度的老化现象。

The stage Ⅱ cofferdam of TGP had been operated successfully for about four years, and was removed in 2002. To summarize the experience of the cofferdam, lots of research work including the site investigation, sampling and field test were done during its removal process and some key issues are analysed. Main conclusions are as follows: ①The dry density of the cofferdam was increased by about 30%;②Both unconfined compression strength and elastic modulus of the seepage proof wall were increased in a certain extent, the ratio of modulus to strength remained basically unchanged, but its permeability coeffecient reduced slightly;③There existed some vertical connecting joints between sections with widths 2～3 mm in the seepage proof wall;④The interface between the seepage proof wall and the weathered sand of cofferdam body was clearly seen filled by mud layer with thickness mostly being 20～30 mm;⑤The intergrality of the overlapping joints between geomembranes was confirmed, but local aging phenomenon was found in the lap joint between geomembrace and the top of the seepage proof wall.