如何在三维有限元计算中反映复合土工膜的力学特性是亟待解决的技术难题。总结了现有的土工膜数值模拟方法，在三维有限元计算中采用薄膜单元来模拟土工膜，建立了某高65 m的高土石围堰土工膜防渗三维有限元模型，土工膜与上、下游坝料接触部位均设置接触。为模拟施工填筑与蓄水全过程，分别计算了土工膜边界柔性约束与刚性约束2种工况。结果表明:薄膜单元较好地反映了土工膜柔性抗拉材料的力学特性，能适应三维有限元数值模拟中常用的分步填筑施工模拟法，且后处理中能直接展示土工膜的位移、应力云图，具有方便高效的特点;土工膜边界柔性约束位移分布均与刚性约束相同，只是最大主应力及拉应力分布区域略小于刚性约束，计算结果符合土石坝工程的一般规律。

To reflect the mechanical properties of composite geomembrane in 3-D finite element calculation is a technical problem to be solved. On the basis of summarizing current numerical methods of geomembrane simulation, we propose to simulate the geomembrane using membrane element in 3-D finite element calculation. By building a finite element model of high earth-rock cofferdam of 65 m height with geomembranes contacted with dam in the upstream and downstream, we simulated the flexible and rigid constraint conditions of geomembrane boundary respectively in filling construction and impounding stages. Results suggest that the membrane element could well reflect the flexible tensile properties of geomembrane. The proposed method could also adapt to the stepped filling in 3-D finite element simulation. Moreover, it could conveniently and effectively display the displacements and stresses of geomembranes in post-processing. The displacement distribution of geomembrane under flexible boundary restraint was the same with that under rigid boundary constraint; while the principal tensile stress and its distributed region under flexible boundary constraint were slightly smaller than those under rigid constraint. The calculation results are consistent with the general rules of earth-rockfill dam.