Models that introduce rolling resistance at the contact are widely employed in simulations using the discrete element method (DEM) to indirectly represent particle shape effects. This approach offers substantial computational benefits at the price of increased calibration complexity. This work proposes a method to simplify calibration of rolling resistance. The key element is an empirical relation between a contact parameter (rolling friction) and a 3D grain shape descriptor (true sphericity). Values of true sphericity can be obtained by image analysis of the grains, either directly by 3D acquisition or by correlation with simpler-to-obtain 2D shape measures. Evaluation of rolling friction is thus made independent from that of other model parameters. As an extra benefit, the variability of grain shape in natural sands can be directly mapped into the discrete model. A mapping between rolling friction and true sphericity is calibrated using specimen-scale and grain scale results from two triaxial compression tests on Hostun sand and Caicos ooids. The mapping is validated using different triaxial tests from the same sands and from other reference sands (Ottawa, Ticino). In the case of Ticino grain-shape acquisition is made in 2D, using an ordinary table scanner. The results obtained support this direct calibration procedure.

使用离散元素方法（DEM）在模拟中广泛采用在接触处引入滚动阻力的模型来间接表示颗粒形状效应。这种方法以增加校准复杂性为代价提供了可观的计算优势。这项工作提出了一种简化滚动阻力标定的方法。关键因素是接触参数（滚动摩擦）与3D晶粒形状描述子（真实球形度）之间的经验关系。可以通过直接对3D图像进行获取或通过与更易于获得的2D形状度量进行关联来对晶粒进行图像分析来获得真实球形度的值。因此，可以独立于其他模型参数进行滚动摩擦的评估。另外一个好处是，天然砂中颗粒形状的变化可以直接映射到离散模型中。使用在Hostun砂岩和Caicos卵石上进行的两次三轴压缩试验的标本比例和晶粒度结果，校准了滚动摩擦与真实球形度之间的映射。使用来自相同砂岩和其他参考砂岩（渥太华，提契诺州）的不同三轴试验验证了映射。在提契诺州的情况下，使用普通的台式扫描仪以2D方式获取晶粒形状。获得的结果支持这种直接校准程序。