# Shear Behaviour of Aeolian Sand with Different Density and Confining Pressure
## 1 Introduction  
With the increase in the construction of people's livelihood projects, such as highways and high-speed railways crossing the desert, the unique mechanical properties of aeolian sand have attracted the attention of researchers. The Wuhai-Maqin Highway of the Zhongwei section is 122.91 km in length, which passes from the southwest to the southern edge of the Tenger Desert, and there are 18 km in the hinterland of the desert. The sand dunes are undulating and the stratum is dominated by the Quaternary Holocene aeolian sand. Due to its arid climate accompanied by year-round strong winds, the shape of aeolian sand is mainly subangular and subcircular [1, 2]. Compared with river sand, the whole grain has less roundness and sharp edges, and is mainly fine grain. As a roadbed material, aeolian sand has engineering characteristics such as collapsibility, strong permeability, and poor gradation. [PERSON] et al. [3] and [PERSON] et al. [4] have shown that aeolian sand has strong collapsibility and the collapsibility has an important relationship with its relative density, moisture content, and fine particle content. [PERSON] et al. [5] proposed a dynamic compactionmethod that can effectively improve the collapsibility of aeolian sand. Considering the compaction characteristics of aeolian sand [6; 7; 8; 9], its compaction curve is \"S\" type, which is totally different from the other types of sand. Namely, the aeolian sand reaches a higher dry density in both the natural state with low water content and the optimum water content, that is, the aeolian sand has the engineering characteristics of wet compaction and dry compaction. More interestingly, as a kind of high permeability material, the permeability of aeolian sand decreases with the increase in dry density [10]. Most of the current research on the mechanical properties of aeolian sand is based on the engineering constructions, such as geotechnical engineering problems encountered in the exploration and development of oil and gas resources in the Mu Us Desert. [PERSON] et al. [11], [PERSON] [12], and [PERSON] [13] conducted a series of static and dynamic triaxial tests on aeolian sand in the Mu Us Desert, and obtained its strength, stress-strain relationship, and pore water pressure change characteristics. In terms of aeolian sand in the Tengger Desert, only [PERSON] et al. [14; 15] conducted true triaxial tests under the condition of drained and undrained, and obtained its mechanical response characteristics with different medium principal stress coefficients. In engineering construction, the bearing capacity of foundation soil is an important property. The bearing capacity of aeolian sand is low and is related to water content [16]. When the bearing capacity of the foundation is insufficient to meet the design requirements, the foundation can be treated by compaction and vibration to improve the bearing capacity and reduce the foundation deformation. After the foundation treatment, the compression modulus of sand increases by 2-18 times [17]. Recently, the jet grouting method for soil mainly containing clean sand is used to decrease liquefaction potential by improving the shear strength of the soil and CPT- and SPT-based analyses confirm the effectiveness of jet grouting [18]. However, the research on the strength and deformation of foundation after the density increases is less, and the effect of foundation treatment is difficult to judge. The research on aeolian sand in this area is almost blank, only the research results on other types of sand. At first, [PERSON] [19] gave the relationship between void ratio and effective principal stress of sand in undrained triaxial tests. [PERSON] et al. [20] and [PERSON] et al. [21] conducted a series of undrained triaxial tests with different void ratios to study the strength characteristics of Toyoura sand, and they concluded that the final stable strength of the sand in triaxial compression was only related to the density, independent of the initial stress level. However, [PERSON] et al.