# State-of-the-Art Research on Loess Microstructure Based on X-ray Computer Tomography
## 4 The Application of CT in Loess Microstructure
### Relationship between Microstructure and Macroscopic Mechanical Behavior of Loess  
As a unique geological material, the relationship between the microstructure and macroscopic mechanical behavior of loess has always been a hot topic in geotechnical engineering and geology. The microstructure characteristics of loess include the morphology, size, arrangement, and orientation of particles and pores, which have a significant influence on the macroscopic mechanical properties of loess, such as strength, deformation characteristics, permeability, and collapsibility. [PERSON] et al. [122] analyzed the macroscopic mechanical properties and the evolution of microstructure in loess, derived a quantitative relationship between CT values and density, discovered that the end restraint effect of the sample was significant under isotropic consolidation conditions, and revealed the variation patterns of CT values under different strain conditions. [PERSON] et al. [123] studied the initial structure and structural changes before and after the shearing of undisturbed and remolded saturated loess through CT experiments, establishing a connection between microstructure and macroscopic mechanical behavior. [PERSON] et al. [124] used X-ray CT and triaxial shear tests to study the impact of the three-dimensional particle structure of Q\({}_{2}\) loess from Jingyang, Shaanxi, on shear behavior. The results showed that the distribution of particle equivalent diameter and sphericity significantly affected shear strength, and the arrangement of particles had an important impact on the shear failure mode. [PERSON] et al. [99,125] used CT scanning technology to establish three-dimensional reconstruction models of Malan loess in the Yan'an New Area during the collapse process under different states and quantitatively characterized the microstructural parameters, revealing the collapse mechanism of Malan loess in the Yan'an New Area through changes in microstructural parameters before and after collapse. [PERSON] et al. [86] constructed a macropore structure model of remolded loess using X-ray CT technology, analyzed the impact of macropores on permeability, and improved image segmentation accuracy through a new workflow. [PERSON] et al. [98], based on micro-CT scanning, conductedundrained shear tests on undisturbed loess, undisturbed saturated loess, and remolded loess, respectively, and analyzed the characteristics of changes in pore structure before and after shearing, providing a basis for the study of the reduction in loess shear strength and the collapse mechanism. [PERSON] et al. [58] summarized the current state of research on the micro-mechanism of loess collapse from three aspects: the composition, properties, and cementation mode of loess cementing substances, microstructural characteristics, and inter-particle forces, and preliminarily explored the collapse mechanism of Malan loess in the Yan'an New Area through case analysis. [PERSON] et al. [126] conducted indoor collapse tests, CT scanning, and mercury intrusion tests to analyze and compare the variation patterns of pore distribution during the collapse process of Malan loess from different regions to explore the collapse mechanism of Malan loess. [PERSON] et al. [127] observed the spatial distribution and morphological evolution of cracks related to the shear failure surface through triaxial shear tests and micro-CT, revealing the development process of local shear failure in Malan loess and providing important insights into the multi-scale simulation of loess mechanical behavior. [PERSON] et al. [128] captured the seepage and storage state of water in the pores of loess based on CT technology, revealing the seepage evolution pattern of dynamic preferential flow. The study found that the loess had a preferential flow phenomenon in both saturated and unsaturated states, with uniformity and anisotropy.