The cone penetration test (CPT) is a major in-situ testing with advantages in efficiency, reliability, and continuous measurement. However, it is often limited in penetration depth in soils such as dense sand and gravel due to high resistance and insufficient pushing force. Studies have shown that rotation can reduce penetration resistance, leading to the development of the rotary CPT. In addition, the torque measurement in rotary CPT could potentially provide extra information for soil behavior. This study simulates regular and rotary CPT tests with varied confining pressure and initial relative density using the discrete element method (DEM). Macroscale results verify that rotation can improve the penetrability of CPT by reducing vertical soil resistance. The reduction mechanism was explained by the microscopic observations and theoretical calculations that rotation can reduce the magnitude of the contact force and tilt its main direction horizontally. To advance the application of rotary CPT, a strong linear correlation between the measurements in rotary and regular CPTs was established, enabling interpretation of the rotary CPT measurements via the vast knowledge accumulated for regular CPT soundings. Furthermore, a theoretical derivation was developed to calculate the soil-probe interface friction coefficient directly by using the measurements of rotary CPT. The influence of the confining pressure, probe friction coefficient, and rotational speed ratio on the calculation accuracy are discussed and explained via particle-scale observations.

中文翻译：

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旋转CPT的离散元建模及其应用

锥入度试验（CPT）是一种主要的原位检测方法，具有高效、可靠、连续测量等优点。但由于阻力大、推力不足，其在密砂、砾石等土壤中的穿透深度往往受到限制。研究表明旋转可以降低贯入阻力，从而导致了旋转CPT的发展。此外，旋转 CPT 中的扭矩测量可能会提供有关土壤行为的额外信息。本研究使用离散元法 (DEM) 模拟不同围压和初始相对密度的常规和旋转 CPT 试验。宏观结果验证了旋转可以通过降低垂直土壤阻力来提高 CPT 的渗透性。通过微观观察和理论计算解释了其减小机制，即旋转可以减小接触力的大小并使其主方向​​水平倾斜。为了推进旋转 CPT 的应用，旋转 CPT 测量值与常规 CPT 测量值之间建立了很强的线性相关性，从而能够通过常规 CPT 测深积累的大量知识来解释旋转 CPT 测量值。此外，还开发了一种理论推导方法，可以利用旋转 CPT 的测量结果直接计算土壤-探针界面摩擦系数。通过颗粒尺度观测讨论和解释了围压、探头摩擦系数和转速比对计算精度的影响。