# Evaluation of Aeolian Sand Collapsibility Based on Physical Indicators in the Mu Us Desert, China
## 1 Introduction  
The Mu Us Desert is located at the junction of Shaanxi Province, the Inner Mongolia Autonomous Region, and the Ningxia Hui Autonomous Region. It is one of the four sandy areas in China. Owing to its unique topography, stratigraphic distribution, vegetation distribution, and climatic conditions, more than 40 types of abundant mineral resources have formed over millions of years of geological evolution, including coal, oil, natural gas, and kaolin. This area has become an important base for China's oil and gas resources and is an important gas source for the \"West-East Gas Transmission\" project [1]. The Changqing Oilfield has more than 100 oil and gas stations in the Mu Us Desert area, with more than 3000 km of oil and gas pipelines. It is one of the largest gas fields, both in China and worldwide. Therefore, it is extremely important to ensure the stability of the foundation of oil and gas stations in the area. However, the main formation in the Mu Us Desert is aeolian sand [2]. Given that there have been few construction projects in this area to date, there has been relatively negligible research on the physical and mechanical properties of this aeolian sand and its foundational stability, including its collapsibility and the evaluation of this trait. Specifically, collapsibility refers to the characteristic of certain soils that, under the influence of a specificpressure, experience rapid structural disintegration upon wetting and consequently exhibit significant additional settlement. Currently, loess is the main object of research for collapsibility. Loess is a widely distributed soil type with a distinctive structure and specific properties [3; 4; 5; 6; 7; 8; 9; 10]. Therefore, loess collapse has received widespread attention. In terms of influencing factors, relationships between particular physical or mechanical parameters in the soil mass and the collapsibility coefficient have mainly been explored using the single-variable method. In this context, previous studies have examined the influencing factors of collapsibility, which mainly include the pressure, water content, natural density, dry density, void ratio, saturation, fine particle content, plasticity index, and liquid index [11; 12; 13; 14; 15; 16]. In terms of the collapse mechanism, research has mainly been conducted from a microscopic perspective or using theoretical modelling to explore the collapse formation process through electron microscopy [17; 18; 19; 20], numerical simulation software [21], constitutive models [22], microstructure models [23], and non-saturation theory [24]. In terms of collapsibility evaluations, previous studies have mainly examined the parameters that affect collapsibility to explore the correlation between single or multiple parameters and the collapsibility coefficient through machine learning algorithms [25; 26; 27; 28; 29] and statistical models [30; 31; 32]. In addition to indirect evaluations, a new method for evaluating collapsibility in situ has been established using time-domain reflectometry [33]. In terms of foundation treatment, the collapsibility coefficient of loess has been reduced using the impact rolling method [34] and vibrating rod compaction method [35]. The research conducted on collapsible loess has encompassed a range of perspectives, from influencing factors to foundation treatment and from macro- to micro-perspectives, providing references for research on the collapsibility of other special soils. In addition to loess, prior research results, which include field surveys, indoor tests, and in situ tests, have shown that aeolian sand is collapsible [36]. [PERSON] [37] demonstrated that South African red sand will collapse when wet under a load, and showed that an open metastable structure is the condition required for its collapse. Later, using scanning electron microscopy, [PERSON] et al. [38] found that kaolinite, which is present in South African red sand, softens when wet, as the large particles move toward large pores.