围堰防渗墙与复合土工膜联接型式试验研究

Study of connecting form between cutoff wall and composite geomembrane

防渗墙上接土工膜是围堰常用的防渗体系,两者变形是否协调是决定防渗成败的关键。以某围堰工程为例,通过围堰防渗体系中复合土工膜的受力分析和复合土工膜与砂砾料界面的直剪摩擦试验,研究了土工膜与填料之间的相互作用,提出了保证土工膜不被拉断应满足的条件。另外,通过离心模型试验监测复合土工膜在堰体与防渗墙变形过程中的应变,揭示了复合土工膜的受力性状和联接部位的破坏机制。结果表明,在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,两种变形不协调均可导致与防渗墙联接部位的土工膜因受拉而破坏,在该基础上提出了改进的土工膜与防渗墙的联接型式和铺设方法。试验成果为指导围堰防渗体系的分析和设计提供了可靠的依据。

The connection effectiveness between cutoff wall and composite geomembrane of cofferdam, both of which are usually applied to the cofferdam, plays an important role in seepage control. Based on the site investigation of stage II cofferdam of Three Gorges Project, through the stress analysis of geomembrane in seepage control and direct shear tests on interface characteristics between composite geomembrane and gravel, the interaction between geomembrane and gravel is studied. The condition to prevent the geomembrane from being broken is proposed. Three centrifuge tests are performed 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 results show that the friction between the composite geomembrane and the cofferdam fillings is so large that the expansion joint reservation cannot work under certain overlying load. Two main influencing factors include the settlement of the weathered sand foundation and the lateral displacement of cutoff wall, both of which play a decisive function in the fracture of the composite geomembrane. Furthermore, an improved method of the connecting form, which made 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 cofferdams.