Macroscopic frictional behavior of granular materials is of great importance for studying several complex problems associated with fault slip and landslides. The main objective of this study is to model the macroscale frictional behavior of granular soils under monotonic and cyclic loadings based upon micromechanical determination of dissipated energy at particle contacts. This study is built on the general observation that the externally computed energy dissipation should be equal to the total internal energy dissipation derived from inter-particle sliding and rolling, energy losses from inter-particle collisions, and damping. For this purpose, the discrete element method is used to model a granular soil and determine the stored, dissipated, and damping energies associated with shear loading for applied monotonic and cyclic velocities. These energies are then related to the friction by an application of the Taylor-critical state power balance relationship. Also, the contributions of the different modes of energy dissipation (normal, shear, and rolling) to the total frictional resistance were studied. By changing the inter-particle friction, the simulations showed that the macroscopic friction was nearly constant, the slip friction increased almost linearly with increasing inter-particle friction, and the difference between the two was attributed to the non-energy dissipating dilatancy component. By providing a clear relationship between energy dissipated by micro-scale mechanisms versus the traditional engineering definition based on macro-scale (continuum) parameters, this study provides a means to develop a better understanding for the frictional behavior of granular media.

颗粒材料的宏观摩擦行为对于研究与断层滑动和滑坡相关的几个复杂问题具有重要意义。本研究的主要目的是基于颗粒接触耗散能量的微观力学确定，模拟颗粒土在单调和循环载荷下的宏观摩擦行为。这项研究建立在一般观察的基础上，即外部计算的能量耗散应等于来自粒子间滑动和滚动、粒子间碰撞的能量损失和阻尼的总内部能量耗散。为此，离散元方法用于模拟粒状土壤，并确定与应用单调和循环速度的剪切载荷相关的存储、耗散和阻尼能量。然后通过应用泰勒临界状态功率平衡关系将这些能量与摩擦相关联。此外，还研究了不同能量耗散模式（法向、剪切和滚动）对总摩擦阻力的贡献。通过改变颗粒间摩擦，模拟表明宏观摩擦几乎恒定，滑动摩擦随着颗粒间摩擦的增加几乎线性增加，两者之间的差异归因于非耗能剪胀分量。通过提供微观机制耗散的能量与基于宏观（连续体）参数的传统工程定义之间的明确关系，本研究提供了一种方法，可以更好地理解颗粒介质的摩擦行为。