Abstract In this study, the three-dimensional discrete element method (DEM) is used to model the unsaturated triaxial test at a low-stress state. The contact model, which considers the matric suction of soils as well as the contact area among particles, and the flexible boundary condition are proposed. Prior to the simulation for the unsaturated triaxial test, we identify the effect of them on the numerical results to get an optimal condition. The deformability of the lateral boundary highly affects the post-peck shear behavior. The specimens with the contact area become brittle like unsaturated soils because it makes interparticle bonding more fragile. According to the comparison of the numerical and experimental results, all the simulations can predict the pre-peck shear behavior as well as the shear strength of unsaturated soils, but some of them underestimate the post-peck shear behavior. In the simulation for the unsaturated soil at a relatively large stress state, the regenerated menisci have a key role in the residual state. In the simulation for the unsaturated soil with higher water content, not only the menisci at contact points but also the bulk water around particles should be taken into account. The particle-scale matric suction in the contact model can exhibit a linear relation with the matric suction of soils, while there is a nonlinear relation between the interparticle stiffness and the matric suction of soils. These relations can be criteria for choosing the input parameters related to the matric suction in further studies. DEM simulation can also provide the microscopic response such as the propagation of the particle-scale fractures and the distribution of particle’s angular velocities.

中文翻译：

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低应力状态下不饱和颗粒材料剪切行为的 DEM 模拟

摘要 在本研究中，三维离散元法（DEM）用于模拟低应力状态下的不饱和三轴试验。提出了考虑土壤基质吸力和颗粒间接触面积的接触模型和柔性边界条件。在对不饱和三轴试验进行模拟之前，我们确定它们对数值结果的影响以获得最佳条件。侧边界的变形能力高度影响后啄剪行为。接触区域的样品变得像不饱和土壤一样脆，因为它使颗粒间的结合更加脆弱。根据数值和实验结果的比较，所有的模拟都可以预测非饱和土的预啄剪切行为和剪切强度，但他们中的一些人低估了啄食后的剪切行为。在较大应力状态下的非饱和土模拟中，再生半月板在残余状态中起关键作用。在模拟含水量较高的非饱和土时，不仅要考虑接触点处的弯液面，还要考虑颗粒周围的大量水分。接触模型中颗粒尺度的基体吸力与土体的基体吸力呈线性关系，而颗粒间刚度与土体的基体吸力呈非线性关系。这些关系可以作为在进一步研究中选择与基质吸力相关的输入参数的标准。