复合土工膜与防渗墙连接的大型剪切试验研究

围堰工程中常用复合土工膜连接防渗墙作为防渗体系,其连接部位的土工膜常会出现结构性破坏而造成集中渗漏现象。依据高土石围堰防渗体系中复合土工膜的受力特点,利用自主研制的低摩阻叠环式双向静动剪切试验机,考虑土工膜无伸缩节、普通竖向伸缩节和U型槽伸缩节3种连接型式,构建复合土工膜与防渗墙接头的结构模型,开展复合土工膜与防渗墙连接的大型剪切试验,研究不同连接型式下复合土工膜的受力变形机理。结果表明:①无伸缩节、普通竖向伸缩节和U型槽伸缩节3种连接型式下,复合土工膜的应变均随着剪切位移的增大逐渐增大,随着距防渗墙距离的增大逐渐减小;②3种连接型式下模型土体的应力-应变关系变化趋势基本一致,峰值应力变化不大;③无伸缩节连接时,靠近防渗墙位置土工膜的峰值应变为4×10^-3,普通竖向伸缩节连接时,相同位置处土工膜的峰值应变为3.5×10^-3,设置U型槽伸缩节后峰值应变为6.51×10^-4,与前2种连接型式相比,U型槽伸缩节较大程度地降低了土工膜的峰值应变,可以有效解决复合土工膜在防渗墙接头处的应变集中问题。研究成果可为高土石围堰工程防渗体系的设计和施工提供依据。

Large-scale Shear Test of the Connection Between Composite Geomembrane and Cutoff Wall

Cutoff wall connected with composite geomembrane is commonly used as an impervious system in cofferdam projects. The geomembrane at the junction often suffers from structural damage and causes concentrated leakage. In line with the mechanical characteristics of composite geomembrane in the impervious system of high earth-rock cofferdam, we established the structural models of the connection between composite geomembrane and cutoff wall considering three connection forms: no expansion joint, ordinary vertical expansion joint, and U-shaped groove expansion joint using a self-developed large-scale bidirectional low friction laminar-ring simple shear apparatus. We further conducted large-scale shear test on the connection between composite geomembrane and cutoff wall to probe into the mechanical deformation mechanism of the composite geomembrane under different connection forms. Results unveiled that in the aforementioned three connection forms, 1) the strain of geomembrane gradually increased with the gradual increase of shear displacement while declined with the growth of distance from the cutoff wall; 2) the variation trend of stress-strain relationship of the model soil didn’t vary much with the connection form, and the peak stress saw no big change; 3) the peak strain of geomembrane near the cut-off wall with no expansion joint was 4×10^-3, with ordinary vertical expansion joints, 3.5×10^-3, and with U-shaped groove expansion joints, 6.51×10^-4. Compared with the other two forms, U-shaped groove expansion joints reduced the peak strain of geomembrane markedly and effectively solved the problem of strain concentration at the junction between geomembrane and cutoff wall.