中文摘要：

为了解黄土三轴剪切过程中的微观变化，采用PFC3D建立黄土三轴试验模型，模拟围压分别为0、50、150、300kPa的三轴剪切试验，并与室内试验进行对比分析。分析结果表明：PFC如能够较好地模拟出不同围压下从开始到破坏到残余变形整个过程中应力一应变的变化规律，且位移场及接触应力场的变化规律与室内三轴试验宏观现象较一致；发现弹性模量、泊松比及峰值强度与数值模型中微观参数有着密切的联系，如法向刚度‰控制试样宏观弹性模量，kn/Ks值控制泊松比，摩擦系数控制峰值强度；通过体应变一轴向应变曲线发现，随着围压的增加应变能增大，试样呈现出由体积膨胀到体积减缩的变化规律。其研究结果为进一步探究黄土的应力一应变性状及抗剪强度特性提供参考。

英文摘要：

In order to research microscopic changes of loess during triaxial shear process, the loess triaxial test model is established with PFC3D （particle flow code in 3 dimensions） software. And the triaxial shear tests are simulated under different confining pressures of 0 kPa, 50 kPa, 150 kPa and 300 kPa. Compared with the results of laboratory triaxial shear tests, the microscopic changes of particles from the beginning then to the peak and at last to the residual deformation of the stress-strain curve are simulated by PFC3D. And the variations of displacement field and contact stress field are more consistent with the macroscopic phenomena of laboratory triaxial tests. The researches indicate that some closely links are existed between the macroscopic parameters （elastic modulus, Poisson＇s ratio, peak strength） of laboratory model and microscopic parameters （normal stiffness, shear stiffness, friction coefficient） of numerical model. For example, the elastic modulus is controlled by the normal stiffness; the Poisson＇s ratio is controlled by the ratio of normal stiffness and shear stiffness; the friction coefficient impacts on the peak strength of stress-strain curve. With the increase of confining pressure, strain energy increases and volume changes in expansion-to-reduction trend. The research result can provide some references for further study of stress-strain behavior and shear strength characteristics of loess.