平均粒径对砂土剪切特性的影响及细观机理

针对平均粒径对砂土剪切特性的影响作用，结合室内试验和离散元模拟方法对不同平均粒径砂土进行了细观研究。基于3种不同平均粒径砂土的直剪试验结果，通过建立反映砂土剪切试验特征的PFC（particle flow code）颗粒流模型，详细研究了不同粒径砂土在剪切过程中土样体积变化、力链网络、孔隙率和配位数等细观结构参数的变化特征和规律，并从细观角度分析了颗粒粒径对土样宏观剪切特性的影响机制。结果表明：具有不同平均粒径砂土的细观结构参数在剪切过程中存在显著差异，并且其细观参数差异主要集中体现在剪切带处；剪切力学特性的影响主要体现在抗剪强度和剪胀效应方面，砂土平均粒径越大，抗剪强度越高，剪胀效应越明显；具有不同平均粒径的砂土在剪切过程中土颗粒运动规律及剪切带形态变化特征存在一定的差异，平均粒径越大，剪切带内上跨式颗粒占比越大，剪切带厚度越大。

Effect of Average Particle Size on Shear Properties of Sand and Its Mesomechanical Analysis

In the view of the effect of average particle size on the shear behavior of sand, a meso-level research was carried out by indoor tests and discrete element simulation methods. Based on the results of three direct shear tests with different average particle size, the PFC (particle flow code) particle flow model reflecting the characteristics of sand shear test was established to study in detail the variation characteristics and laws of soil sample changes, force chain network, porosity, coordination number,and other microscopic structural parameters of sandy soil with different particle sizes during the shear process;And the effect of particle size on the macroscopic shear behavior was analyzed from the microscopic perspective. The research results demonstrate that there are significant differences in the sand shear meso-parameters with different average particle sizes, and the differences are mainly reflected in the shear zone. The effect of average particle size of sand on its shear mechanical properties is mainly reflected in its shear strength and dilatancy deformation. The larger the average particle size is, the higher the shear strength is,and the more obvious the dilatancy effect is. There is a certain difference between the soil particle movement law and the morphological change characteristics of the shear zone during the shearing process:the larger the average particle size is, the larger the proportion of up span particles in the shear band is, and the larger the thickness of the shear band is.