基于混凝土/岩石界面动态断裂性能研究的混凝土重力坝地震断裂

With the large-scale development of China's western region, many high concrete gravity dams have been or are being built in this seismically active region. The safety of dams in strong earthquakes has been a crucial issue, in which the dam-foundation interface is the weak link. Since the interface acts as the joint between the concrete and rock, its fracture behavior is very complicated, with the strain rate and loading mode-mixity being the two main factors. Through fracture experiment and numerical simulation, the proposed project will investigate the influence of the two factors. Fracture parameters including the initiation toughness, propagation toughness and propagation velocity at the concrete/rock interface will be measured. A numerical model on the interfacial fracture of brittle materials under moderate strain rate will be established based on the Scaled boundary finite element method. The influence of strain rate and mode mixity will be investigated, the mechanism of interfacial fracture will be studied. On this basis, a seismic fracture model of the dam-foundation interface will be constructed, in which the influence of dam-foundation-reservoir interaction will be properly taken into consideration. The crack propagation along the interface and kinking will be tracked, leading to the simulation of the complete process of crack initiation, propagation and failure of the dam. The influence of factors including the mismatch of concrete and rock, as well as the water pressure inside the crack will be clarified. Through the proposed research, our knowledge on the fracture mechanism of gravity dams in earthquakes will be deepened, and a new effective approach will be presented for the seismic stability evaluation of gravity dams.

伴随着我国西部水力资源的大开发，多座高混凝土重力坝在西部强震区开工建设，确保大坝在强地震作用下的安全至关重要。坝基界面是重力坝稳定的薄弱环节，因涉及到混凝土和岩石两种材料，其断裂特性非常复杂，应变率和加载模态比是其中最重要的两个影响因素。本项目从试验和数值模拟两方面开展研究，测定混凝土/岩石界面在地震应变率和不同加载模态比下的起裂韧度、裂缝扩展韧度和裂缝扩展速度，并基于比例边界有限元法建立准脆性材料界面在中低应变率下的高精度断裂数值模型，综合试验和数值模拟结果阐明应变率和模态比的耦合影响，揭示界面断裂机理。在此基础上，建立考虑坝-地基-库水相互作用影响的坝基地震断裂模型，跟踪坝基裂缝沿界面扩展和偏折路径，开展大坝起裂-裂缝扩展-失稳全过程模拟，并阐明混凝土和岩石力学参数不匹配程度、缝内水压等因素的影响。本项研究将深化对混凝土重力坝坝基断裂机理的认识，并为重力坝地震稳定评价提供有效手段。

伴随着我国西部水力资源的大开发，多座高混凝土重力坝在西部强震区开工建设，确保大坝在强地震作用下的安全至关重要。坝体与地基之间的界面是重力坝稳定的薄弱环节，往往成为强震区高混凝土坝建设的制约因素。但因涉及到混凝土和岩石两种材料，坝基面的断裂特性非常复杂，需基于界面力学理论和断裂动力学理论进行研究，应变率和加载模态比是其中最重要的两个影响因素。本项目采用试验和数值模拟对地震特征应变率范围内的混凝土/岩石界面断裂开展研究，并推广至重力坝的地震断裂模拟，以期为强震区高重力坝的建设提供依据。在通过试验测定混凝土和岩石各自的动态断裂特性的基础上，通过轴向拉伸、劈拉和三点弯曲试验测定了混凝土/岩石界面在拉伸模态下的动态断裂特性，分析了应变率的影响，研究了准脆性材料界面断裂与两种母材断裂机制的异同。考虑到重力坝坝踵裂缝处于复合断裂模态的特点，通过四点剪切试验研究了混凝土/岩石在复合断裂模态下的断裂特性，分析了加载模态比与应变率的耦合影响。发展了基于比例边界有限元法的断裂计算模型，包括提出了任意裂纹面荷载作用下的界面断裂模型，引入有限断裂法的复合断裂准则解决了裂缝扩展步长的确定问题，以及采用等几何分析进行几何造型和离散提高计算精度等。在以上研究的基础上，提出了重力坝地震水力劈裂模型，可全面考虑坝-库水-地基动力相互作用、缝水相互作用和裂缝面接触等因素的影响。所采用的坝-库水-地基相互作用模型能够考虑无限地基辐射阻尼、库水的可压缩性和库底的吸收条件；提出的缝-水相互作用模型可以考虑裂缝面粗糙程度和水体在裂缝内流动状态；多边形网格技术可实现网格全自动重剖分。采用该模型研究了坝面裂缝和坝踵裂缝的扩展过程，分析了缝内水压和坝体/地基材料参数不匹配性的影响，获得了重力坝裂缝的扩展过程和断裂路径。本项研究为强震区高重力坝的抗震安全评价提供了新的思路和完整的计算模型。