Compacted granular material, integral to geotechnical engineering, undergoes translation, rotation, and interlocking when subject to shear displacements or external loads. The present study focuses on the interlocking of heterogeneous granular materials, a complex behavior influenced by gradation, compaction, and varying particle geometry, and has consequently received limited attention in existing research. To address this research gap, we conducted an analysis on the effect of grain interlocking on the shear resistance of granular assemblies, using a combination of laboratory testing and the discrete element method (DEM). Initially, large-scale direct shear tests were conducted on gravel−sand mixes with varying degrees of compaction and normal pressure. One of the mixes also underwent subsequent shear reversal to explore the differences in grain interlocking between the two shearing processes on the shear plane. After analyzing the laboratory results, a mesoscopic scale investigation was performed by replicating the test using discrete element simulations. To facilitate this, granular particle geometries were measured using 3D laser scanning based on the physical lab tests. Subsequently, based on these scans, discrete element R-block and ball models were utilized to construct both the coarse and fine particles within the mix. Surface vibro-compaction was employed to regulate the degree of compaction. The results indicate that an increase in vertical pressure, coupled with a zero dilatancy angle, results in a rising stress ratio, indicative of grain interlocking. This interlocking exhibits a positive correlation with both the coarse content and the degree of compaction, and varies depending on the shear displacement. As interlocking progresses, the shear band, induced by particle movement, expands and is associated with reduced particle rotation near the shear band. The study further reveals a consistent positive correlation between interlocking and the principal orientation angle of strong normal contact forces, as well as a correlation between interlocking and mobilized contacts.

中文翻译：

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剪切颗粒集合体中颗粒互锁的联合实验和 DEM 研究

压实颗粒材料是岩土工程的组成部分，当受到剪切位移或外部载荷时，会发生平移、旋转和联锁。目前的研究重点是异质颗粒材料的连锁，这是一种受级配、压实和变化的颗粒几何形状影响的复杂行为，因此在现有研究中受到的关注有限。为了弥补这一研究空白，我们结合实验室测试和离散元方法 (DEM)，对颗粒互锁对颗粒组件抗剪性能的影响进行了分析。最初，对具有不同压实程度和常压的砾石-砂混合物进行了大规模直剪试验。其中一种混合物还进行了随后的剪切反转，以探索剪切平面上两个剪切过程之间颗粒互锁的差异。分析实验室结果后，通过使用离散元模拟重复测试来进行介观尺度研究。为了实现这一点，根据物理实验室测试，使用 3D 激光扫描测量颗粒的几何形状。随后，根据这些扫描，利用离散元 R 块和球模型来构建混合物中的粗颗粒和细颗粒。采用表面振动压实来调节压实程度。结果表明，垂直压力的增加加上零剪胀角会导致应力比上升，这表明晶粒互锁。这种联锁与粗粒含量和压实程度呈正相关，并根据剪切位移而变化。随着互锁的进行，由颗粒运动引起的剪切带扩展，并与剪切带附近颗粒旋转的减少相关。该研究进一步揭示了联锁和强法向接触力的主方向角之间一致的正相关性，以及联锁和移动接触之间的相关性。