堆石料流变的细观机理与粘弹塑性本构模型研究

Large amounts of prototype observations show that high earth-rock dams present considerable post-construction deformation. The underlying mechanism of this phenomenon is the degradation of the particle strength due to environmental changes and the particle breakage under high contact stresses. Neglecting the rheological behaviour of earth-rock dams induced by degradation and breakage of particles often results in a underestimation of the deformation of the shell and the anti-seepage system of the dams, and thus gives an exaggerated prediction on the long-term safety of the dams. In this study, creep and stress relaxation experiments will be carried out on specific dam materials, and an elastoplastic model, takes the particle strength parameter as an separate variable, will be established. The long-term deformation observations of typical prototype dams will be analyzed so that the mathematical representation for the degradation of the particle strength parameter can be formulated. The fulfillment of establishing a viscoelastoplastic model will then be achieved by combining the degradation function of the particle strength parameter with the elastoplastic model. The proposed viscoelastoplastic constitutive model will be embedded into an existing finite element simulation program and used to investigate the rheological properties of the shell and the anti-seepage systems for extremely high earth-rock dams with a height near 300 meters. A discrete element code will also be adapted so as to model the degradation of the particle strength and the induced particle breakage. The DEM procedure will be used to simulate the rheological processes of an earth-core rockfill dam and a concrete face rockfill dam, respectively. The variation of the contact forces, the contact orientations and other internal fabric quantities within the rockfill materials will be investigated in depth. The experimental, theoretical and numerical investigations conducted in this research are expected to deepen the understanding on the rheological properties of earth-rock dams and to provide a theoretical foundation for predicting the long-term stress-deformation behaviour of extremely high earth-rock dams in a reasonable manner.

大量原型观资料表明高土石坝运行期存在显著的后期变形，其机理是堆石料在环境因素作用下的劣化和高接触应力下的破碎。忽略颗粒劣化和破碎引起的流变会低估坝壳与防渗系统的变形量，并对高土石坝的长期安全性作出偏于危险的评价。本项目将针对筑坝堆石料开展蠕变与应力松弛试验，在此基础上建立以颗粒强度为参变量的弹塑性模型；研究分析典型高土石坝的长系列变形原型观测资料，提出颗粒强度参量随时间衰减的数学模型；耦合颗粒强度衰减模型与弹塑性模型，构建可合理反映堆石料流变过程的粘弹塑性本构模型。开发粘弹塑性有限元计算程序，研究300m级超高土石坝的流变特性；开发考虑强度衰减和颗粒破碎的离散元计算程序，对心墙坝和面板坝的流变过程进行细观模拟，揭示土石坝流变过程中接触力、接触方向等组构量的演化规律。本项目研究可深化对堆石坝流变机理的科学认识，为合理预测超高土石坝工程的长期应力变形特性提供理论支撑。

大量原观资料表明高土石坝运行期存在显著的后期变形，其机理是堆石料在环境因素作用下的劣化和高接触应力下的破碎。忽略颗粒劣化破碎引起的流变会低估坝壳与防渗系统的变形量，并对高土石坝的长期安全性作出偏于危险的评价。本项目分析了典型高土石坝的长系列变形原型观测资料，揭示了筑坝堆石料流变随时间的指数型演化规律；针对筑坝堆石料开展了大型三轴流变试验，发现加载与流变过程中塑性应变方向明显不同；基于广义塑性理论，建立了可以统一模拟堆石料加载变形与流变的粘弹塑性本构模型；开发了高土石坝长期变形分析的有限元计算软件，研究了300m 级超高土石坝的变形特性；开发了考虑颗粒强度衰减和颗粒破碎的离散元计算程序，对堆石料的流变过程进行细观模拟，揭示流变过程中接触力、接触方向等组构量的演化规律。上述研究成果有助于深化对堆石料流变机理的认识，并为我国超高土石坝应力变形预测提供了更加符合实际的本构模型，有望显著提高其应力变形预测的精度与可靠性。