Understanding the frictional characteristics of granular materials (e.g., fault gouge and sand foundations) exposed to dynamic normal load are important for investigations of engineering geology disasters and safety assessment. Direct shear tests on granular materials under dynamic normal load were performed in the laboratory using a dynamic shear box device. Experimental results showed that the shear strength and normal displacement varied with variations of normal load, identified by a phase shift and normal stress loading peak. The peak shear stress decreased with increasing normal load frequency and shear velocity, in particular, the peak shear stress changed nonlinearly with the increase of normal load amplitude, characterized by a critical point. The influence of normal load amplitude on the shear strength and normal displacement was analyzed in detail. Furthermore, the results showed that dynamic normal load can both enhance and reduce the shear strength on granular material, and the frictional behaviors were velocity-amplitude-frequency dependent, which can be well interpreted by the Rate and State Friction constitutive law. These findings provide guidance in the design of geotechnical engineering projects when dynamic normal loads are encountered (e.g., blasting, earthquakes, earth tides and reservoir effects).

了解暴露在动态法向载荷下的颗粒材料（例如断层泥和沙地基）的摩擦特性对于工程地质灾害调查和安全评估很重要。在实验室中使用动态剪切箱装置在动态法向载荷下对颗粒材料进行直剪试验。实验结果表明，剪切强度和法向位移随法向载荷的变化而变化，由相移和法向应力载荷峰值确定。峰值剪应力随着法向载荷频率和剪切速度的增加而减小，特别是峰值剪应力随着法向载荷幅值的增加呈非线性变化，表现为一个临界点。详细分析了法向荷载幅值对剪切强度和法向位移的影响。此外，结果表明动态法向载荷可以增强和降低颗粒材料的剪切强度，并且摩擦行为与速度-幅度-频率相关，这可以用速率和状态摩擦本构定律很好地解释。当遇到动态法向载荷（例如，爆破、地震、土潮和水库效应）时，这些发现为岩土工程项目的设计提供了指导。可以很好地解释速率和状态摩擦本构法。当遇到动态法向载荷（例如，爆破、地震、土潮和水库效应）时，这些发现为岩土工程项目的设计提供了指导。这可以很好地解释为速率和状态摩擦本构法。当遇到动态法向载荷（例如，爆破、地震、土潮和水库效应）时，这些发现为岩土工程项目的设计提供了指导。