# State-of-the-Art Research on Loess Microstructure Based on X-ray Computer Tomography
## 4 The Application of CT in Loess Microstructure
### The 3D Characterization of Loess Microstructure  
With further advancements in technology, micro-CT with higher scanning precision began to be applied to the study of the microstructure of loess. Some scholars combined high-precision micrometer-level CT images with three-dimensional image reconstruction software to quantitatively analyze the microstructural characteristics of loess, such as particle size, particle sphericity, pore distribution, pore orientation, and pore connectivity, thereby analyzing the macroscopic disaster mechanisms of loess. For example, [PERSON] et al. [107] used computed tomography and fractal theory to propose a quantitative method for studying the three-dimensional morphology of large pores in loess, finding that the fractal dimension reflects the irregularity of the pore contour and is inversely proportional to moisture content, density, and cohesion, and directly proportional to porosity, providing a new method for the study of soil microstructure. [PERSON] et al. [108] conducted CT scanning on saturated fine-grained soil in Daya Bay, using Avizo 9.0 software for the quantification and characterization of the three-dimensional pore structure and analyzing its consolidation and creep mechanisms from a micro- and nano-scale perspective. [PERSON] et al. [109], based on micro-CT scanning, established three-dimensional images, conducted quantitative analysis of the two-dimensional pore area of Malan loess and qualitatively characterized its three-dimensional structure. [PERSON] et al. [110, 111] conducted CT scans on loess and found that the large structural units of loess exhibited significant concentration in the vertical direction. By analyzing the geometric parameters of the loess pore structure, they considered loess to be a geological material with strong anisotropy. [PERSON] et al. [112] used Avizo to establish a pore grid model of loess and paleosol, discovering that the content of clay particles determined their role in the soil skeleton, thereby affecting the pore structure. Through real-time loading-unloading CT triaxial tests, comparing the pore characteristics of original loess, compacted loess, and remolded loess, [PERSON] et al. [113] observed that the pristine loess exhibits a higher degree of interconnected porosity compared to its compacted counterpart. Furthermore, they noted that compacted loess and the original loess, despite possessing identical dry densities, exhibit distinct pore configurations. [PERSON] et al. [25] explored the micron-scale three-dimensional microstructure characteristics of loess in the Jingyang area, Shaanxi Province, China. Using X-ray-computed tomography technology, combined with image segmentation methods, they quantitatively analyzed the size, shape, and arrangement of loess particles and pores. The study found that two-dimensional analysis results could not fully reflect the characteristics of the three-dimensional microstructure, which had a reference value for understanding the microstructure of loess and similar granular materials. [PERSON] et al. [114] used high-precision CT to quantify the structural and pore distribution patterns of remolded loess made by compaction and tamping methods. [PERSON] et al. [115]conducted a quantitative analysis of the microstructure, such as the pores and throats of Yan'an Q\({}_{2}\) loess, based on micro-CT. Most of the above studies are based on discussions of static parameter changes between different samples and cannot account for the impact of inter-sample discrepancies on the experimental outcomes. To address this, [PERSON] et al. [116] developed a micro soil sample hydro-mechanical loading system that could perform CT scans on different conditions of the same soil sample; it is a method that can effectively reduce the impact of sample errors on the experiment. Additionally, some researchers have integrated CT scanning with continuous sectioning techniques to investigate the microstructure of loess. For example, [PERSON] et al.