# CT Scanning of Structural Characteristics of Glacial Till in Moxi River Basin, Sichuan Province
## 1 Introduction  
G Glacial till is a special kind of soil that is directly deposited by detritus in the melting process of Quaternary glacier. It shows poor sorting, wide distribution of grain size and complex structure. In China, glacial till is widely distributed in high-altitude areas such as the Tianshan Mountains, Qinghai-Tibet Plateau and other mid-high latitude mountainous areas. Its thickness can reach hundreds of meters and its scale can be hundreds of millions of cubic meters [1,2]. Due to the special climate of alpine mountainous areas, freeze-thaw cycles often occur, resulting in changes in the structure of glacial till, a reduction in strength, and the induction of engineering and geological disasters [3]. It poses a serious threat to people's lives and to property and engineering construction. However, there are few systematic research results on its structure. Glacial till's formation is due to glacial movement and has not been significantly modified by other external forces. Generally, it does not have beddings. The gravel in the soil has poor roundness, and is mostly prismatic and sub-prismatic [1]. Studies have shown that the lithology, mineral composition and content of glacial till are mainly related to the nature of the bedrock in the source area, while the distribution characteristics of the particle size are mainly related to the type of glacier, transport and deposition methods [4]. In view of the structural characteristics of glacial till, many studies have taken the particle size parameter, particle size frequency curve, particle size accumulation curve, and particle size scatter diagram as an important basis basis for dividing glacial till from other mixed accumulation soils [5]. The meso-structure of glacial till refers to the cementation and state of cementation, relative position, contact state, size and shape of the pores between the particles of soil and rock clasts. The meso-structure of glacial till plays a decisive role in its physical and mechanical properties and strength, which can also reflect the macroscopic movement of glaciers. The mesoscopic characteristics of glacial till can not only indicate the macroscopic movement process of glaciers, but also determine the physical and mechanical properties of the soil [6; 7]. The cementation between soil particles and the state of cementation are the controlling factors of the strength of glacial till, while the pore structure has a significant impact on the engineering characteristics of glacial till [7; 8]. The texture, especially the content of sand, can transform the pores of glacial till under the conditions of freeze-thaw, water content and stress difference; this results in a change in pore structure, causing the problems of expansion, softening and instability of the glacial till, which have a certain impact on engineering construction [9; 10]. The micro-structure of the particle arrangement of the glacial till and the orientation of the particles also have a great influence on its mechanical properties. The orientation and the degree of fragmentation of the particles increase with the increase in pressure, which leads to a decrease in the strength of the glacial till [11]. In recent years, with the construction of major national projects such as the Sichuan-Tibet railway and highway, engineering geological problems caused by glacial till have become increasingly prominent. At present, the engineering and geological characteristics of the glacial till still remain insufficiently investigated. On the one hand, this is due to the complexity of glacial till formation; on the other hand, it is limited by research methods [5]. The study of the mechanical properties of glacial till is the key to studying the engineering and geological properties of glacial till, including meso-structure characteristics and fabrics; indoor and in situ mechanical tests and mechanical models; and numerical simulation of deformation and failure [12].