Loess is an aeolian, nonstratified deposit. Loess collapsibility is considered to be closely related to its microstructure. The three-dimensional (3D) microstructure of loess specimens was established based on serial X-ray computed tomography (CT) images with a voxel size of 1 μm³. The loess microstructure and parameters, including the particle size, sphericity, and orientation and pore size distribution were characterized qualitatively and quantitatively in 3D space. In addition, the microstructural evolution during collapse based on the 3D microstructure was also analyzed to interpret the mechanism of loess collapse combined with X-ray diffraction and scanning electron microscopy results. The results highlight that loess collapsibility originates from both microstructural and compositional characteristics. The studied loess has an open structure with widely distributed spaced pores and inter-particle or inter-aggregate pores. Brick-shaped and subangular particles with tilted orientations and point-to-point contacts maintain a vulnerable, metastable structure. Carbonate and clay aggregations between particles endow the loess with a high strength in the natural state. Under loading and wetting, the swelling and dispersion of clay aggregation, particularly the degraded illite and interstratified illite - montmorillonite, and the loss of high suction initiate structural failure. During collapse, particles primarily move down in a vertical or tilted direction with little rotation. Pores are most sensitive to loading and wetting; during collapse, the distributions of the pore number and volume percentage become more unimodal. The pore connectivity becomes weaker. Pores larger than 23 μm decrease in pore number under wetting, and pores larger than 26 μm decrease in volume percentage.

黄土是风成的，非分层的矿床。黄土的湿陷性被认为与其微观结构密切相关。三维（3D）黄土试样的显微组织建立了基于与1μm的体素尺寸的串行X射线计算机断层扫描（CT）图像³。在3D空间中定性和定量地表征了黄土的微观结构和参数，包括粒径，球形度，取向和孔径分布。此外，还基于3D微观结构分析了塌陷过程中的微观结构演变，结合X射线衍射和扫描电子显微镜结果解释了黄土塌陷的机理。结果表明，黄土的湿陷性起源于微观结构和组成特征。所研究的黄土具有开放的结构，其具有广泛分布的间隔开的孔以及颗粒间或聚集体间的孔。具有倾斜方向和点对点接触的砖状和亚角颗粒保持脆弱的亚稳结构。颗粒之间的碳酸盐和粘土聚集使黄土在自然状态下具有高强度。在加载和润湿下，粘土聚集体的膨胀和分散，特别是降解的伊利石和层状伊利石-蒙脱石，以及高吸力的丧失引发了结构破坏。在坍塌过程中，粒子主要沿垂直或倾斜方向向下移动而几乎不旋转。毛孔对加料和润湿最敏感。在塌陷期间，孔数和体积百分比的分布变得更单峰。孔的连通性变弱。大于23μm的孔在润湿下的孔数减少，大于26μm的孔的体积百分比减少。尤其是降解的伊利石和层状伊利石-蒙脱石，高吸力的丧失会引发结构破坏。在坍塌过程中，粒子主要沿垂直或倾斜方向向下移动而几乎不旋转。毛孔对加料和润湿最敏感。在塌陷期间，孔数和体积百分比的分布变得更单峰。孔的连通性变弱。大于23μm的孔在润湿下的孔数减少，大于26μm的孔的体积百分比减少。尤其是降解的伊利石和层状伊利石-蒙脱石，高吸力的丧失会引发结构破坏。在坍塌过程中，粒子主要沿垂直或倾斜方向向下移动而几乎不旋转。毛孔对加料和润湿最敏感。在塌陷期间，孔数和体积百分比的分布变得更单峰。孔的连通性变弱。大于23μm的孔在润湿下的孔数减少，大于26μm的孔的体积百分比减少。孔数和体积百分比的分布变得更单峰。孔的连通性变弱。大于23μm的孔在润湿下的孔数减少，大于26μm的孔的体积百分比减少。孔数和体积百分比的分布变得更单峰。孔的连通性变弱。大于23μm的孔在润湿下的孔数减少，大于26μm的孔的体积百分比减少。