Nanoparticles found in rock avalanches and natural faults were inferred to be the reason for the ultra-low shear resistance of the materials along the shear surface. Nevertheless, this inference has not been physically verified yet. To investigate the role of nanoparticles in the shear behavior of granular materials, we conducted a series of ring shear tests on silicon dioxide nanoparticles (SN), silica sand (S8), and mixtures of the S8 with different contents of SN, under varying normal stresses (σ) and shear velocities (). Our results showed that the shear strength (μ) of SN is high when σ is small (≤ 215 kPa at our test range), even though the maximum shear velocity is about 210 cm/s, but shows a great decrease under higher σ (≥ 619 kPa). The shear strength of mixtures varied with SN content. For S8 (M0) and the mixture of 10% SN (M10), when sheared under small σ, μ first decreased slightly with increasing when is smaller than 1 cm/s, after that it increased slightly with further increase of . Nevertheless, this kind of shear-rate dependent behavior was not observed in the tests under higher σ. When the content of SN in the mixture was <20%, μ increased with the increase of SN content. However, with further increase of SN content, μ decreased. Under high normal stress conditions, distinctive powder rolls were observed on the shear surface formed on the tests. When the mixtures with lower SN content (≤50%), the powder rolls were not observed. We inferred that powder rolls can be produced under high SN content and high normal stress conditions, and this structure altered the particle movement mode from sliding friction to rolling resistance, resulting in a significant decrease in the shear strength. These findings provide valuable insights into the shear behavior of granular materials with nanoparticles and then provide evidence for a better understanding of the high mobility of rock avalanches.

中文翻译：

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纳米材料对干砂混合物残余剪切强度的机械效应：对岩石雪崩高流动性的影响


岩石雪崩和自然断层中发现的纳米颗粒被推断是材料沿剪切面具有超低剪切阻力的原因。然而，这一推论尚未得到物理验证。为了研究纳米粒子在颗粒材料剪切行为中的作用，我们对二氧化硅纳米粒子（SN）、硅砂（S8）以及不同SN含量的S8混合物在不同的法向剪切力下进行了一系列环剪试验。应力 (σ) 和剪切速度 ()。我们的结果表明，当 σ 较小时（在我们的测试范围内≤ 215 kPa），SN 的剪切强度 (μ) 较高，尽管最大剪切速度约为 210 cm/s，但在较高 σ 下表现出大幅下降（ ≥ 619 kPa）。混合物的剪切强度随SN含量的变化而变化。对于S8（M0）和10％SN（M10）的混合物，在小σ下剪切时，μ首先在小于1 cm/s时随着增加而略有减小，之后随着σ的进一步增加而略有增加。然而，在较高 σ 下的测试中并未观察到这种与剪切速率相关的行为。当混合物中SN含量<20%时，μ随着SN含量的增加而增加。然而，随着SN含量的进一步增加，μ减小。在高法向应力条件下，在测试中形成的剪切表面上观察到独特的粉末卷。当SN含量较低（≤50%）的混合物时，未观察到粉末卷曲现象。我们推断，粉末卷可以在高SN含量和高正应力条件下生产，这种结构改变了颗粒运动模式从滑动摩擦到滚动阻力，导致剪切强度显着下降。 这些发现为了解纳米颗粒颗粒材料的剪切行为提供了宝贵的见解，然后为更好地理解岩石雪崩的高流动性提供了证据。