砂砾土颗粒三维形态分布特征及其离散元模拟

Characterization and Discrete Element Modeling of the 3D Morphology of Sand-gravel Mixtures

砂砾土是一种典型的具有非均质性、非连续性及构成结构效应的砂-砾混合料,混合料中砂粒与砾粒的接触状态对其力学特性影响显著.使用图像处理技术提取了砂砾土中不同粒径砾粒的三维尺寸(长轴长度、中轴长度、短轴长度以及长短轴比)和棱角系数,研究了三维尺寸和棱角系数的均值、标准差和统计分布,结果表明其具有统计自相似性特点.采用多面体和棱角系数来共同描述砂砾土颗粒三维形态.基于PFC3D(Particle Flow Code)颗粒流离散元计算程序,提出了砂砾土颗粒三维形态的离散元生成算法,模拟了砂砾土的三轴排水剪切试验过程,通过与室内试验结果的对比分析验证了模型方法的有效性.试验结果从细观机理层面揭示了砂砾土试样在排水剪切过程中颗粒运动规律以及颗粒间接触力链分布,有助于理解和解释混合料的非线性力学行为.

Sand-gravel mixtures are typical binary materials,which exhibit highly heterogeneous and discontinuous behavior,and thus have significant structural effect.The contact state between the sand and gravel particles has a significant influence on the mechanical properties of the mixtures.We extract the particle size(i.e.length,width,height of the soil particle and ratio between length and width),and the angularity and surface texture(AT)index of aggregates,and analyze the correspondent means,standard deviations and statistical distributions.The results indicate that the particle size and the AT index of sand-gravel mixtures have strong statistical similarities.An algorithm for generating 3D aggregates is thereby developed based on the statistical results of the coarse aggregates 3D morphology,assuming that the coarse aggregates are hexahedron,pentahedron and tetrahedron.The algorithm is realized using the Fish language in the particle flow code(PFC3D).The numerical model is then applied to conduct a 3D shear testing simulation.Retrospective simulation of a laboratory test using the proposed model show good agreement,calibrating the reliability of the proposed algorithm.The results interpret well the mechanism of particle motion and the distribution of interparticle contact force chain during shearing from the meso-scale viewpoint,which can give better understanding and modeling the nonlinear behavior of sand-gravel mixtures.