In this study optical flow method is used for soil deformation measurement in laboratory tests. The main objective was to observe how the deformation distributes along the whole height of cylindrical soil sample subjected to torsional shearing (TS test). The experiments were conducted on dry non-cohesive soil samples under two different values of isotropic pressure. Samples were loaded with low-amplitude cyclic torque to analyze the deformation within the small strain range (0.001-0.01%). Optical flow method variant developed by Ce Liu (2009) was used for motion estimation from time-ordered series of images. This algorithm uses scale-invariant feature transform (SIFT) for image feature extraction and coarse-to-fine matching scheme for faster calculations. The results show that while the displacement values change approximately monotonically along sample's height, displacement field is very different for samples under different isotropic pressure. Moreover, the deviations from assumed linearity distribute differently during different stages of the same TS test.

中文翻译：

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测量扭剪作用下土样变形的光流法

在这项研究中，光流方法用于实验室测试中的土壤变形测量。主要目的是观察变形如何在承受扭转剪切作用的圆柱状土壤样品的整个高度上分布（TS试验）。在两个不同的各向同性压力值下，对干燥的非粘性土壤样品进行了实验。样品加载有低振幅循环扭矩，以分析在较小应变范围（0.001-0.01％）内的变形。由刘策（2009）开发的光流方法变型用于从按时间顺序排列的一系列图像进行运动估计。该算法使用尺度不变特征变换（SIFT）进行图像特征提取，并使用粗略匹配方案进行快速计算。结果表明，尽管位移值沿样品高度近似单调变化，但在不同的各向同性压力下，样品的位移场却有很大差异。此外，在同一TS测试的不同阶段，与假定线性的偏差分布不同。