围堰防渗墙与复合土工膜联接型式离心模型试验研究

防渗墙上接复合土工膜是围堰常用的防渗体系,联接部位的有效性是决定防渗成败的关键.以某围堰工程为原型开展离心模型试验,通过监测复合土工膜在堰体与防渗墙变形过程中的应变,揭示复合土工膜的受力性状和联接部位的破坏机理.结果表明一定上覆荷载作用下,复合土工膜与堰体之间的摩阻力超过其所承受的拉伸力,导致预留伸缩节不能发挥作用;复合土工膜下部风化砂的固结变形使之与刚性防渗墙之间产生较大的差异沉降,以及防渗墙与上游堰体的水平脱离,此两种变形不协调均可导致与防渗墙联接的复合土工膜因受拉而破坏.基于此,提出了防渗墙与复合土工膜联接型式的改进方法,使联接部位的复合土工膜不承受拉应力,通过离心模型试验验证其合理性和可行性,为指导围堰防渗体系的设计和施工提供了可靠的试验依据.

Centrifugal model tests on connecting form between cutoff wall and composite geomembrane of cofferdam

The connection effectiveness between cutoff wall and composite geomembrane of cofferdam, both of which are usually applied in the cofferdam, plays an important role in seepage control. Based on the site invitation of stage II cofferdam of Three Gorges Project, three centrifuge tests are performed in order to reveal the mechanism of the connecting form of cutoff wall and composite geomembrane by measuring the displacements of the cofferdam fillings and cutoff wall and the strain of the composite membrane. The friction between the composite geomembrane and the cofferdam fillings is so large that the expansion deformation reservation cannot work. Two main influencing factors include the settlement of the weathered sand foundation and the lateral displacement of cutoff wall, which both play a decisive function in the fracture of the composite geomembrane. Furthermore, an improved method of the connecting form, which make the composite geomembrane not be tensioned, is proposed and validated by centrifuge tests. The improved method provides a reliable evidence for the design and construction of the seepage control system of cofferdams.