空心圆柱扭转仪定向剪切试验离散元模拟

为分析砂土在复杂应力条件下的剪切力学特性，采用商业离散元软件PFC3D对单粒组中密砂的空心扭剪试验进行了仿真模拟，分析了数值试样的应力-应变关系，研究了不同剪切方向下离散介质的强度、体积应变特性以及中主应力比对它们的影响，再现了力链在加载过程中的演化，并对剪切带的倾角做了深入分析。同时，从细观上看，以颗粒接触数和纯转动率变量为中心，观察了试样内部颗粒的运动状态，对比了不同剪切方向下剪切带内外颗粒接触数与纯转动位移的变化。最后，将数值试验结果与已有的室内试验结果进行了对比。此研究实现了复杂应力条件下空心扭剪试样的三维离散元模拟，加深了对空心扭剪试验过程和结果的理解和解释。

Discrete element simulation for torsional shear test by hollow cylinder apparatus

This paper presents results of three-dimensional simulations of the hollow cylinder test using the discrete element method (DEM). To verify the capability of numerical model, the hollow cylinder specimens are sheared at different principal stress directions. The localization in the specimen are examined in terms of the distributions of stresses and strains. The force chain formation and collapse during the loading are visualized. Meanwhile, the formation of the shear bands in the different shearing directions is characterized by porosity and shear strain rate distributions in the samples. The results show that the shear strain rate contour is a better indicator for shear band development than the porosity contours. To explore the micro behavior of the specimen, the evolutions of coordination number and particle rotation at different locations in the sample are also monitored. It is proved that 3D DEM technique can capture the macro-micro behavior of specimen in the complex stress path, which facilitate the interpretation of the stress-strain behavior from physical lab tests.