Abstract: The conventional triaxial test was simulated by DEM software PFC2D and PFC3D， and the inf1uence of model di mension on DEM studies was analyzed from the macro mechanical behaviors and the micro fabric characteristics. Numerical simulation results indicate that , stress-stain curves of densest 2D and 3 D numerical specimens both show obvious softening characteristics , the slrains cOlTesponding to the peak strength of 3D specimens are 75% smaller than that of 2D specimens. The peak strenglhs of both specimens iricrease with confining pressure , and the peak strength of 3D specimen under high confining pressure becomes larger than that of 2D specimen. The shapes of macro shearing band of 2D and 3D numerical specimens are different under the same confining pressure level , which are determined by the distribution of tangential contact force between particles. The increase of the confining pressure makes the distribution of tangential contact force between particles of the DEM specimens tend to the contact normal distribution , which is in the form of concentrated shear band of speclmen m macro.

Key words: road engineering, geotechnical engineering, distinct element code( DEM) , model dimension, shear band, distribution of contact force

摘要： 借助离散元程序——颗粒流PFC，对实验室常规三轴试验分别进行了三维和二维数值试验，从试样宏观力学响应和微观结构特征的角度，分析了模型维数对离散元研究的影响。数值试验结果表明：处于最密实状态的、模型参数相同的三维和二维数值试样，剪切试验中均表现出软化的特征，但三维数值试样达到峰值强度所对应的应变约为二维数值试样的1/4。两种维数数值试样峰值强度均随围压增大而增大，高围压下三维试样峰值强度变为大于二维试样峰值强度。相同围压下，不同维数数值试样宏观剪切带的形状不同，其是由颗粒间切向接触力的分布规律决定的；围压增大使离散元试样内颗粒间切向接触力的分布趋于接触法向的分布范围，宏观上表现为试样剪切带变得集中。

关键词: 道路工程, 岩土工程, 离散元, 模型维数, 剪切带, 接触力分布