The study of the mesostructure of soil under loading is the basis for understanding its macromechanical properties and for establishing its constitutive model. In this study, a series of shear tests was performed on dry calcareous sand under constant normal stress by a modified direct shear apparatus. Digital images of the sample at different shear stages are obtained. The mesostructural parameters of the sample are then extracted and analyzed using an image analysis technique. The results show that the shear-band is located at the junction of the upper and lower shear boxes with a thickness of 0.79–1.59 mm. During shearing, the position of the maximum shear strain incremently shifted to the junctions between the two shear boxes. The azimuths of the particles prior to the test distribute symmetrically on both sides of 90°. After the test, the azimuths of the particles are mainly obtuse angles (150–180°) and the long axis of the particles generally points in the opposite direction from the shear-band. The sand particles undergo four stages: random arrangement during initial sample preparation, compaction under normal stress, particle rotation during shearing, and ordered alignment after shearing. The test results help to reveal the movement mechanism of calcareous sand at the mesoscopic level during the direct shear process.

中文翻译：

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用数字成像方法研究钙质砂质材料的介观剪切行为

对载荷作用下土壤细观结构的研究是了解其宏观力学性质和建立其本构模型的基础。在这项研究中，通过改良的直接剪切设备，在恒定法向应力下对干燥钙质砂进行了一系列剪切试验。获得了处于不同剪切阶段的样品的数字图像。然后使用图像分析技术提取并分析样品的细观结构参数。结果表明，剪切带位于上，下剪切盒的交界处，厚度为0.79–1.59 mm。在剪切过程中，最大剪切应变的位置逐渐移至两个剪切盒之间的连接处。测试之前，粒子的方位角在90°的两侧对称分布。经过测试 粒子的方位角主要是钝角（150-180°），粒子的长轴通常指向与剪切带相反的方向。砂粒经历四个阶段：初始样品制备过程中的无规排列，法向应力下的压实，剪切过程中的颗粒旋转以及剪切后的有序排列。测试结果有助于揭示石灰岩在直接剪切过程中在介观水平上的运动机理。