# CT Scanning of Structural Characteristics of Glacial Till in Moxi River Basin, Sichuan Province
## 5 Discussion
With the introduction of CT, compared with other technologies, CT technology has the advantages of real-time and non-destructive detection that can perform non-invasive scanning of the internal structure of objects. It is one of the most direct and accurate methods of characterizing the micro-structure of rock and soil mass, and it can carry out real three-dimensional reconstruction of rock and soil mass materials. Because the high-precision CT scanning technology has been unanimously recognized by experts and scholars, it has been extended to the geotechnical engineering community in recent years [43; 44; 45; 46]. The research of CT scanning technology in soil is mainly concentrated on special soils such as loess, expansive soil, frozen soil, and coarse-grained soil. Among them, there is very little research on frozen soil, and the research direction mainly focuses on theevolution of soil micro-structure. The combination of triaxial shear test and CT scanning technology tracks the dynamic change characteristics of the soil structure under the action of force, which has played a good role in understanding the three-dimensional physical characteristics of the soil. Most of the research results relate to the use of intuitive CT images and the size and distribution of CT numbers to analyze and evaluate the micro-structure of the soil and its deformation and mechanical mechanisms [47]. Freezing and thawing is an important research topic in the field of frozen soil engineering. In recent years, there has been much research on soil freezing and thawing, and fruitful research results have been obtained. The existing results have basically ascertained the influence characteristics of freezing and thawing on soil porosity, permeability, particle size gradation, mineral composition and soil strength. Moreover, they have revealed the variation laws of soil strength, shape and particle size with the increase in cyclic freezing and thawing times. The periodic freezing and thawing process makes the structure of the soil undergo a strong change. During the cyclic freezing and thawing process, the water inside the soil migrates and redistributes, the pores and particle sizes change, the particles are rearranged, and the bonding force between the soil particles is destroyed, resulting in weakening of the soil structure. In addition, freezing and thawing have a two-way effect on the density of soil. The density of loose soil increases and the void ratio decreases, while the density of compact soil decreases and the void ratio increases [48]. These structural changes are changes in the physical and mechanical properties of the soil, which seriously reduce the physical and mechanical properties and durability of the soil [49]. The changes in the engineering geological properties of these soils will directly affect the stability of the foundation and superstructures. For example, a series of disasters such as subsidence, structural fracture, and foundation uplift will occur. Therefore, the impact of cyclic freezing and thawing on the engineering geological properties of soil has attracted more and more attention [50]. Glacial till is a special soil in alpine mountainous areas. Under the influence of the special climate in alpine mountainous areas, seasonal or day-night cycles of freezing and thawing are prone to occur. What is the correlation between the destruction process and mechanism of the meso-structure and micro-structure of glacial till before and after cyclic freezing and thawing? What are the critical hydraulic parameters required for the initiation of debris flow? These are important topics that have not yet been researched in depth, and need to be studied urgently. The research results can provide a basis for disaster prevention and mitigation and major project construction in alpine mountainous areas.