基于比例边界有限元-离散元耦合法的堆石料蠕变细观机理研究

Particle breakage and rearrangement are the main causes of creep deformation in rockfill materials. Excessive creep will endanger the stability and safety of rockfill dam. Numerical analysis method of particle breakage and microscopic creep mechanism of rockfill materials are the research hotspots in recent years. Convex polygons are used to model the rockfill aggregates. The particles’ motion and interaction are solved by discrete element method (DEM). The stress and strain of each particle is analyzed by using the scaled boundary finite element method (SBFEM). The Hoek-brown criterion is introduced to determine the particles’ broken, which is combined with the fractal theory to describe particle breakage. The particle strength attenuation model considering the time effect is adopted to establish a coupled Scaled Boundary Finite - Discrete Element Method for the microscopic creep analysis of rockfill materials. This new method takes advantages from both DEM and SBFEM at the same time. The visible biaxial compression tests and creep tests are taken to verify the validity of the numerical method, the macro-micro deformation characteristics of rockfill materials are also revealed. The microscopic mechanism of the creep of the rockfill materials is revealed by the comprehensive analysis of the laboratory tests and numerical simulation results from particle’s view, which includes microscopic mechanical properties of particle’s contacts, normal contact forces and frictional contact forces, it also includes microscopic deformation properties of particle’s transnational movement, rotation and particle breakage. This research can enrich the numerical simulation method of particle breakage and reveal the creep mechanism of high rockfill dam from the microscopic view.

颗粒破碎和重组是导致堆石料产生蠕变的主要原因，过大的蠕变会危害堆石坝的稳定和安全。颗粒破碎数值分析方法及堆石料蠕变的细观机理是近年来的研究热点。本项目拟以凸多边形模拟堆石料复杂形状，采用离散单元法求解颗粒运动及其相互作用，通过比例边界有限单元法对颗粒内部进行应力应变分析，引入Hoek-Brown准则判断其破坏，结合分形理论描述颗粒破碎，引入考虑时间效应的颗粒强度衰减模型，建立一种分析堆石料蠕变细观机理的比例边界有限元-离散元耦合法，可同时发挥离散元和比例边界有限元的优势；开展可视化室内双轴压缩及双轴蠕变试验，揭示堆石料宏细观变形特性演化机理，同时为数值模拟提供对比验证；综合室内试验及数值模拟结果，从颗粒尺度层面（颗粒接触、法向接触力及切向接触力等细观力学特性和颗粒滑移、转动及破碎等细观变形特性）揭示堆石料蠕变细观机理。研究成果可以丰富颗粒破碎数值模拟的手段，深入揭示高堆石坝蠕变的细观机理。

颗粒破碎和重组是导致堆石料产生蠕变的主要原因，过大的蠕变会危害堆石坝的稳定和安全。颗粒破碎数值分析方法及堆石料蠕变的细观机理是近年来的研究热点。本项目首先研制了可视化堆石料双轴压缩测试系统并开展可视化室内双轴压缩试验，揭示堆石料宏细观变形特性演化机理，同时为数值模拟提供对比验证；同时以凸多边形模拟堆石料复杂形状，采用离散单元法求解颗粒运动及其相互作用，通过比例边界有限单元法对颗粒内部进行应力应变分析，引入Hoek-Brown准则判断其破坏，开发了两种颗粒破碎模式，建立了模拟堆石料颗粒破碎的比例边界有限元-离散元耦合分析方法SBFDEM并对比了不同破坏模式下对堆石料力学特性的影响；基于离散元提出一种考虑颗粒复杂形状并满足破碎前后系统质量与能量守恒的破碎模型，并引入劣化效应重现堆石料的蠕变行为，从颗粒尺度层面（颗粒接触、法向接触力及切向接触力等细观力学特性和颗粒滑移、转动及破碎等细观变形特性）揭示了堆石料蠕变细观机理。结果表明：相同围压作用下，颗粒球度与试样强度成正比，颗粒粒径与试样强度成反比；破碎颗粒分布演化可直观体现破碎颗粒实时的数量及位置，内部颗粒速度场分布反映颗粒的运动与加载方向之间具有一致性，颗粒间平均接触力由小到大与宏观应力变化规律一致，力链结构趋向密集的特性也可反映出随加载进行试样体积剪缩与破碎颗粒数量的增加；试样体积变形与内部颗粒破碎集中发生在主压缩阶段，蠕变阶段的变形量和新增破碎颗粒数量较少，随围压增大试样变形及颗粒破碎速度加快，最终变形量及破碎率提高，颗粒破碎率演化与试样体积变形随时间发展呈现高度的一致性。研究成果丰富了颗粒破碎数值模拟的手段，揭示了高堆石坝蠕变的细观机理。