The development of a miniature triaxial apparatus is presented. In conjunction with an X-ray microtomography (termed as X-ray μCT hereafter) facility and advanced image processing techniques, this apparatus can be used for in situ investigation of the micro-scale mechanical behavior of granular soils under shear. The apparatus allows for triaxial testing of a miniature dry sample with a size of 8 mm × 16 mm (diameter × height). In situ triaxial testing of a 0.4–0.8 mm Leighton Buzzard sand (LBS) under a constant confining pressure of 500 kPa is presented. The evolutions of local porosities (i.e., the porosities of regions associated with individual particles), particle kinematics (i.e., particle translation and particle rotation) of the sample during the shear are quantitatively studied using image processing and analysis techniques. Meanwhile, a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking. It is found that the sample, with nearly homogenous initial local porosities, starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress. In the post-peak shear stage, large local porosities and volumetric dilation mainly occur in a localized band. The developed triaxial apparatus, in its combined use of X-ray μCT imaging techniques, is a powerful tool to investigate the micro-scale mechanical behavior of granular soils.

中文翻译：

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微型三轴仪器，用于利用原位X射线显微断层扫描技术研究颗粒状土壤的微力学

提出了微型三轴仪的发展。结合X射线显微断层照相术（以下简称X射线μCT）设备和先进的图像处理技术，该设备可用于原位研究颗粒状土壤在剪切作用下的微观力学行为。该设备可对尺寸为8 mm×16 mm（直径×高度）的微型干燥样品进行三轴测试。原位提出了在500 kPa的恒定围压下对0.4-0.8 mm Leighton Buzzard砂（LBS）进行的三轴测试。使用图像处理和分析技术定量研究了样品在剪切过程中的局部孔隙度（即与单个颗粒相关的区域的孔隙度），颗粒运动学（即颗粒平移和颗粒旋转）的演变。同时，提出了一种基于局部孔隙率和颗粒跟踪结果量化样品体积应变分布的新方法。发现样品具有接近均一的初始局部孔隙率，开始在偏应力峰值附近开始表现出明显的局部孔隙率不均匀性以及颗粒运动学和体积应变的局部化。在峰后剪切阶段，大的局部孔隙度和体积膨胀主要发生在局部带中。结合使用X射线μCT成像技术而开发的三轴仪，是研究粒状土壤微观力学行为的有力工具。