SmartRock has recently been adopted in obtaining the particle-scale characteristics of ballast track and gives microscopic explanation of track performance under cyclic loads, such as degradation and reinforcement. We notice that the contact state of individual ballast particles changes with loading cycles, which in reverse gives rise to different particle movements. The changes of contact state and particle movements may accumulate as loading cycle increases and could be considerable. This makes the response of individual particles uncertain and thus brings practical difficulties in evaluating the performance of ballast track via particle-scale characteristics, especially for long-term loading. In order to learn more about the response uncertainty of individual particles, this study conducts a full size model test to investigate the variation of particle movement and inter-particle normal contact force with loading cycle, amplitude as well as frequency by using SmartRocks. The equivalent axle load ranges from 14 to 36 t, the frequency of the cyclic loading varies from 1 to 18 Hz. Two smart rocks were placed below the sleeper end and the shoulder region respectively. It is found that the long-term variation of particle’s movements and contact force with loading cycle show obvious fluctuation due to the continuous accumulated changes of particle’s contact state. While particle’s movements are generally stable during short-term loading. The movements of SmartRock beneath sleeper end are positively correlated with loading magnitude and frequency, nevertheless also shows a characteristic independent on loading cycles, magnitude as well as frequency: particles’ rotation in horizontal plane is mainly permanent rotation (accumulated rotation), while particle’s rotation in planes perpendicular to the lateral and longitudinal directions is mainly recoverable rotation. The influences of loading magnitude and frequency on ballast particle movements are found different. The results provide effective particle-scale indicators for investigations related to ballast track.

中文翻译：

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使用SmartRock传感器表征与加载周期，幅度和频率相关的压载颗粒的运动

SmartRock最近已被用于获得压载道的颗粒级特征，并给出了在循环载荷（例如退化和加固）下轨道性能的微观解释。我们注意到，单个压载颗粒的接触状态会随着加载循环而变化，反过来会引起不同的颗粒运动。接触状态和粒子运动的变化可能会随着加载周期的增加而累积，并且可能是相当大的。这使得单个颗粒的响应变得不确定，从而给评估通过颗粒尺寸特性的道ast轨道的性能带来实际困难，尤其是对于长期载荷而言。为了更多地了解单个粒子的响应不确定性，这项研究进行了全尺寸模型测试，以研究颗粒运动和颗粒间法向接触力随载荷周期，振幅和频率的变化，方法是使用SmartRocks。等效轴负载范围为14至36 t，周期性负载的频率范围为1至18 Hz。在枕木末端和肩部区域下方分别放置了两个智能岩石。研究发现，由于颗粒接触状态的不断累积变化，颗粒运动和接触力随载荷循环的长期变化表现出明显的波动。虽然在短期加载过程中粒子的运动通常是稳定的。SmartRock在轨枕末端下方的运动与载荷的大小和频率呈正相关，尽管如此，它也显示出与载荷周期无关的特性，大小和频率：粒子在水平面中的旋转主要是永久旋转（累积旋转），而粒子在垂直于横向和纵向的平面中的旋转主要是可恢复的旋转。发现负载量和频率对压载颗粒运动的影响是不同的。结果为与压载轨道有关的研究提供了有效的颗粒尺度指标。