碾压混凝土高坝水力劈裂的多尺度实验和数值模拟研究

The heels and construction interfaces of high roller compacted concrete (RCC) dams under high water head are susceptible to dangerous hydraulic fracture which may lead to reservoir leakage, local damage or even complete failure. This is an unsolved key problem in the design and operation of RCC dams. This proposal is aimed at elucidating the mechanisms of hydraulic fracture across micro, meso and macro scales by developing a multiscale numerical method based on in-situ micrometer X-ray computed tomography (XCT) tests. Three-dimensional images showing the whole process of hydraulic fracture under different water pressures will be acquired first by the in-situ XCT tests of standard-sized specimens. Imaged based mesoscale finite element models (FEM) coupling the seepage and stress fields will then be built, validated and analyzed to understand the evolution of damage and fracture until failure and reveal the micro/mesoscale seepage-stress-fracture coupling mechanisms. Finally, an efficient multiscale numerical method based on the FEM and the scaled boundary FEM will be developed to study the macroscale hydraulic fracture mechanisms of high RCC dams in a view to provide strong scientific basis for the establishment of design criteria and safety assessment guidelines against hydraulic fracture under high water head in the future.

碾压混凝土(RCC)高坝的施工层面和坝踵区域在高水头作用下存在水力劈裂的危险，可能导致库水渗漏、局部损坏甚至整体溃坝，是RCC大坝设计和运行过程中悬而未决的关键问题。 本项目以阐明RCC渗流-应力耦合作用下高压水力劈裂的跨微观、细观、宏观力学机理这一科学问题为目标，提出以微观X光计算断层扫描(XCT)原位加载实验为基础的多尺度数值模拟方法。采用XCT-高压水力劈裂集成装置进行标准试件实验，获得不同水压下水力劈裂全过程的三维微观图像；建立并实验验证基于微观图像的渗-力耦合细观有限元(FEM)模型，精确模拟高水头下试件内部断裂损伤演化直至破坏的全过程，揭示RCC材料特别是在施工层面和坝踵附近的微细观渗流-应力-断裂耦合机理；开发耦合FEM和比例边界FEM的高效多尺度模拟算法，阐明RCC高坝水力劈裂的宏观破坏机理，为下一步建立抗高压水劈裂的设计公式和安全评价准则提供强有力的理论基础。

碾压混凝土高坝的施工层面和坝踵区域在高水头作用下存在水力劈裂的危险，可能导致库水渗漏、局部损坏甚至整体溃坝，是大坝设计和运行过程中悬而未决的关键问题。本项目以阐明混凝土渗流-应力耦合作用下高压水力劈裂的跨微观、细观、宏观力学机理这一科学问题为目标，提出以微观X射线计算断层扫描(CT)原位加载实验为基础的多尺度数值模拟方法。采用CT-劈裂集成装置进行原位实验，获得不同荷载下劈裂全过程的三维微观图像；建立并实验验证基于微观图像的渗-力耦合细观有限元(FEM)模型，精确模拟试件内部断裂损伤演化直至破坏的全过程，揭示微细观渗流-应力-断裂耦合机理。本项目分别建立了基于微观CT图像、随机骨料、魏布尔随机场的混凝土渗流-应力-断裂耦合模型，初步实现了有限元法FEM和比例边界有限元法SBFEM相结合、分别基于离散粘性界面单元方法和连续粘性损伤相场方法的水力劈裂多尺度数值模拟算法的开发，对进一步阐明高坝水力劈裂的宏观破坏机理、建立抗高压水力劈裂的设计公式和安全评价准则具有重要理论和工程实际意义。