高土石坝防渗土工膜局部力学和渗漏特性研究

Earth-rock dam with impervious geomembrane barrier is currently one of the most development potential new dam type. However, various types of damages and defects will inevitably occur in production, construction and operation for geomembrane. The mechanical property of geomembrane which is layed on upstream dam surface or in dam center is very complicated. Under the action of high water pressure, the damages and defects of geomembrane will develop contineously, the local unsaturated seepage field of dam body behind the geomembrane will evolve dynamiclly, and they will interact with each other. In this study, the biaxial and uniaxial tensile test and direct shear test, resistance to breakdown test, and seepage test due to defects of geomembrane with damages and defects will be carried out under different cases in order to realy simulate the complicated local mechanical and seepage properties of geomembrane in high earth-rock dams. Using membrane mechanics, damage and fracture mechanics, and seepage theory, the evolution law of damages and defects, seepage elements, erosion of soil particles and coupled mechanism will be studied by theoretical analysis, mathematical and mechanical modelling. The finite element simulation, with Multi-scale adaptive grid tracking technology, will be conducted for the coupled unsaturated-unsteady seepage field and stress field of high earth-rock dams with impervious geomembrane barrier, with emphasis on the spatial-temporal evolutionary process of local mechanical and seepage behaviors of defects, leakage due to defects and interaction, which will affect the local seepage stability and overall safety of the dam. Finally, the safety assessment system for high earth-rock dams with impervious geomembrane barrier will be put forward. The investigation results will have a significant guidance on the construction of high earth-rock dams with impervious geomembrane barrier, and promote the development of this dam type safely and quickly.

土工膜防渗土石坝是当前极具发展潜力的新坝型。土工膜在生产、施工及运行中会不可避免地造成局部损伤或缺陷。高土石坝坝面或坝内防渗土工膜受力性状复杂，在高水头作用下其局部损伤或缺陷会不断发展，同时形成动态演化的坝体非饱和缺陷渗流场，且两者之间互相影响。本项目拟开展不同损伤或缺陷条件下土工膜拉伸、剪切、抗击穿和缺陷渗漏试验，较真实模拟土工膜复杂的局部受力变形和渗漏行为。采用薄膜力学、损伤和断裂力学及渗流等相关理论对损伤或缺陷发展规律、缺陷渗流要素、垫层颗粒流失及相互作用进行理论分析、数学和力学建模。采用多尺度自适应网格追踪技术，进行随机损伤或缺陷分布下土工膜防渗高土石坝渗流应力耦合分析，探明土工膜缺陷扩展、缺陷渗漏等局部力学和渗流特性的时空变化规律，分析其对大坝局部稳定和整体安全的动态影响，建立相应的评价体系。研究成果对土工膜防渗高土石坝的建设具有重要的理论指导作用，促进该坝型安全快速发展。

土工膜在生产、运输和施工中会不可避免地造成局部损伤或缺陷，同时由于高土石坝中土工膜局部受力特性复杂，运行期土工膜也可能出现局部动态变化的损伤或缺陷，引起的缺陷渗漏可能对大坝防渗安全造成不利影响。项目紧密围绕土工膜局部力学特性和渗漏特性两大核心问题，开展了复杂条件下土工膜拉伸、剪切、顶破、液胀（水力击穿）、局部变形及缺陷渗漏等系列试验，较真实模拟实际工程中土工膜的局部受力变形和渗漏行为，取得了相应的研究成果。具体：①利用3D-DIC技术精准测定缺陷附近区域土工膜拉伸时的应变分布规律，深入分析了不同缺陷形式下土工膜的强度、泊松比和应变等力学性能，探明了缺陷附近应变集中规律及缺陷演化机理。②剖析了缺陷和损伤对土工膜顶压变形特性的影响规律，探明了不同垫层类型、含水率和压实度下土工膜顶压变形发展规律及破坏形式，揭示了土工膜-垫层相互作用机理。③研究了不同土工膜厚度、损伤度、变形边界条件下土工膜液胀变形规律，揭示了土工膜液胀变形机理和破坏特征（水力击穿），建立了土工膜液胀应力-应变数学模型。④深入剖析了垫层类型、垫层粒径、上覆水压对土工膜局部变形的影响规律，辨识了颗粒垫层上土工膜局部破坏特征，创建了上覆水压与下垫层颗粒粒径之间的理论关系式，提出了土工膜免受破坏的颗粒最大粒径选取方法。⑤细致分析了垫层类型、法向压力、剪切幅值、剪切速率、循环次数对土工膜界面剪切特性的影响规律，探明了直剪与循环剪切条件下土工膜-垫层界面剪切强度演变机理，获得了界面剪切劲度、阻尼比及其变化规律，建立了直剪和循环剪切条件下界面本构模型，并进行了数值仿真应用。⑥研究了垫层类型、垫层含水率和压实度及缺陷位置对垫层缺陷渗漏浸润区的影响规律，建立了相应的数学模型；揭示了膜下垫层孔压、含水率分布特征及扩展演化规律，探明了缺陷渗漏形成机制与发展路径。⑦深入研究了缺陷数量、大小、位置对膜后大坝局部饱和区及垫层渗透坡降的影响规律；剖析了库水变化条件下缺陷渗漏对坝面土工膜局部抗滑稳定性及坝坡稳定性的影响规律。项目总体完成情况好，达到了预期研究目标，取得了较丰富的研究成果，对土工膜防渗（高）土石坝的设计、施工和运行管理具有重要的理论指导作用，促进我国土工膜防渗（高）土石坝工程安全快速发展。