循环荷载下堆石料塑性应变增量演化规律研究

In the current study, the behaviors of rockfill material under cyclic loading mainly focuses on the relations between residual strain and cyclic strain amplitude as well as the cyclic number. The researches on the stress-dilatancy (related to the direction of plastic strain increment), hardening rule (related to the magnitude of plastic strain increment) and particle breakage (affecting the plastic strain increment) under cyclic loading are still rare. Besides, due to lack of elaborate experimental data, the generalized plasticity model used to evaluate the seismic-induced deformation of large geotechnical structures is empirical in describing the plastic strain increment with key assumptions under cyclic loading. In order to solve the existing problem, a series of large-scale cyclic triaxial tests will be conducted to study the stress-dilatancy, the hardening rule and the particle breakage. The expressions of stress-dilatancy equation, hardening parameter and particle breakage parameter are modified to reflect the changing rule of plastic strain increment, and incorporated into the existing generalized plasticity model. The elastic-plastic finite element procedure based on the modified generalized plasticity model will be used to evaluate the dynamic responses of rockfill dam during strong earthquake. The study will provide the significant reference for anti-seismic safety design for high rockfill dam in strong ground motion zone.

目前堆石料循环变形试验分析主要研究残余应变与应变幅值和循环次数之间的关系，对采用弹塑性理论描述堆石料循环变形所需的剪胀规律(与塑性应变增量的方向有关)、屈服硬化规律(与塑性应变增量的大小有关)及颗粒破碎规律(影响塑性应变增量的方向和大小)的研究较少，循环荷载下堆石料塑性应变增量演化规律尚不可知。此外，由于缺少精细的试验数据，目前已应用于大型土工建筑物地震安全评价分析的广义塑性模型(及改进模型)，在描述循环荷载下的塑性应变增量时(包括大小和方向)有较大的经验性，其对数值计算中地震变形的影响尚不可知。本项目拟采用大型三轴仪，首先系统地研究堆石料的循环剪胀、硬化和颗粒破碎规律，然后建立循环荷载下堆石料剪胀方程、硬化参数和颗粒破碎参数的表达式；在此基础上，改进和完善堆石料广义塑性模型并开发相应的分析平台，开展高土石坝动力弹塑性数值模拟，为强震区高土石坝的抗震设计提供理论支撑。

堆石料变形是评价这些高土石坝抗震安全性的重要内容。本项目围绕堆石料的力学特性和本构模型两个基础问题进行了系统的研究。首先提出了一种无扰动的大型三轴试验中堆石料试样橡皮膜嵌入量测量方法，解决了复杂路径条件下堆石料体变测量精度低的难题。在此基础上，揭示了不同加载路径条件下堆石料剪胀的应力路径相关性和颗粒破碎量与塑性功的应力路径无关性，为堆石料本构模型的改进提供了试验依据。在双机制理论框架下，引入比例记忆的概念，建立了一个反映不规则循环加载影响的堆石料弹塑性本构模型，并将其植入到自主开发的有限元计算软件GEODYNA。最后开展了高土石坝动力弹塑性数值分析研究，验证了提出本构模型和开发软件的先进性。研究成果可为强震区高土石坝的抗震安全评价和结构优化设计提供技术支撑。