考虑库水位循环的土心墙堆石坝坝顶裂缝产生机理与演化规律研究

The crest crack is a common risk of earth core rockfill dam. The existence of the crest crack greatly increases the safety risk of the project. Observed data shows that the formation of crest crack is closely related to the change of reservoir water level. However, the influence mechanism of reservoir water level on the crest crack is not clear yet. This project intends to carry out centrifugal model test toward earth core rockfill dam, and study the effect of reservoir water cycles and water level rising and falling speed on the long-term deformation of dam body and the formation and propagation of crest crack. On this basis，revealing the mechanism and evolution law of crest crack under the long-term circulation of reservoir water level. Then, the discontinuity of the crack is described by using the displacement model of XFEM, and the horizontal set function is used to track the geometry of the crack. To simulate the formation and evolution of the crest crack, the calculation program is developed by embedding the classical constitutive model, wetting and rheological model. The computing program is optimized based on the results of centrifuge model test. Finally, combining with the observed data of a typical earth-rockfill dam, the formation and evolution process of the crest crack are simulated to investigate the primary causes of the crest crack. The final development form of the crest crack is predicted, and the safety and stability of the dam is evaluated. Consequently, the corresponding prevention and control measures are put forward. The research results can deepen the understanding of the mechanism and evolution law of crest crack, which is beneficial to improve the level of safety and control of actual earth core rockfill dam.

坝顶裂缝是土心墙堆石坝常见病险，它的存在大大增加了工程的安全风险。实测资料表明坝顶裂缝的形成与库水位变化密切相关，但库水位变化对坝顶裂缝的影响机制尚不十分明确。本项目拟针对土心墙堆石坝开展离心模型试验，研究库水位循环次数和水位升降速度对坝体长期变形及坝顶裂缝形成与扩展的影响；揭示库水位长期循环下坝顶裂缝的产生机理与演化规律。然后，采用扩展有限元的位移模式描述裂缝的间断性，引用水平集函数追踪裂缝的几何特性；改进并嵌入经典本构、湿化及流变模型，开发能够模拟坝顶裂缝形成与演化过程的计算程序并依据离心模型试验结果对程序进行优化。最后，结合某典型土心墙堆石坝实测资料，对其坝顶裂缝的形成及演化过程进行模拟，探讨坝顶裂缝发生的根本原因；预测裂缝最终发展形态；评价坝顶裂缝对坝体长期安全稳定性的影响并提出相应的防治措施。研究成果可深化对土心墙坝坝顶裂缝机理和演化规律的认识，有益于提高土石坝工程安全防控水平。

采用申请人研究团队自主研发的带有库水位控制系统的400gt离心模型试验系统，对某模型坝进行了离心试验，分别研究了库水位循环次数和水位升降速度对坝体长期变形及坝顶裂缝形成与扩展的影响；揭示了库水位长期循环下坝顶裂缝的产生机理与演化规律。研究发现，模型在库水压力的作用下上下游易发生差异变形，一方面是库水推力，另一方面是上游坝壳料湿化变形，由于筑坝料的流变变形，两者共同产生的差异变形在离心力的加载过程中变大，直至坝顶部位土体拉应力降低到抗拉强度，坝顶裂缝随机产生。采用以缝尖为圆心，一定倍数特征网格长度为半径，进行富集区划分的方法来扩展该区域节点自由度，以此计算裂缝的非连续位移场；采用子单元积分方法进行含裂缝不连续单元的积分，给出了积分子域内的积分方案，结果表明该方案可准确计算积分点的应力状态。建立了土体张拉-剪切破坏准则。依据计算得到的单元内拉应力系数ηt和剪应力系数ηs来判定裂缝发生的位置，给出了首次开裂方向的判定方法；基于对裂缝尖端应力集中和重分布的研究，提出了运用扇形面区域控制方法来判定裂缝扩展方向的具体方案。开发了土心墙堆石坝坝顶裂缝计算软件，对某高心墙堆石坝坝顶裂缝发生及发展过程进行了模拟模拟。发表论文多篇，其中第一作者发表SCI论文4篇，EI论文11篇，会议论文3篇，申请发明专利5项，授权发明专利3项，出版专著1部。期间还获得中国博士后科学基金一等资（2018M630578）、中国博士后科学基金特别资助（2019T120444）等4项基金项目。本项目成果已成功应用于小浪底斜心墙堆石坝、瀑布沟高心墙堆石坝以及苗尾心墙堆石坝的坝顶裂缝模拟中。