# Shear Behaviour of Aeolian Sand with Different Density and Confining Pressure
## 1 Introduction
[22; 23] found through an experimental study that the effective mean principal stress has a greater influence on the stress-strain relationship of sand than the density of sand. Considering the influence of density on the strength and deformation of sand, [PERSON] et al. [24] and [PERSON] et al. [25] found that there was an approximately linear relationship between the relative density and the friction angle of specimens. [PERSON] et al. [26] used 3D digital imaging technology to study the deformation behaviour of sand with different relative densities during triaxial tests, and found that the inclination of the failure surface did not in accordance with either the Coulomb or Roscoe criterion. In the past, sand with different densities or subjected to different confining pressures were generally considered to be different materials [27]. In order to understand this complex behaviour, different state parameters have been proposed and incorporated into the stress-dilatancy equation [27; 28; 29]. Static liquefaction is a common failure mode for loose sand, [PERSON] and [PERSON] [30] incorporated it into a state-dependent constitutive model to capture this behaviour. However, the deformation characteristic of aeolian sand is still unclear due to the lack of relevant tests. In addition, the shear behaviours of aeolian sand are also very unique. According to the particle size distribution curve, the grain size of aeolian sand mainly distributes in the range of 0.1-0.25 mm, which can be classified as a fine sand. However, some of the widely accepted facts about clean quartz sand and silty sand seem to be inapplicable to fine sand [31]. The critical state theory is the basic theoretical of many constitutive models used in engineering design, which has played an increasingly important role in the study of the mechanical behaviours for granular materials [32; 33]. Many studies have shown that the critical state line (CSL) in the plane of \(q\)-\(p^{\prime}\) and \(e\)-\(lnp^{\prime}\) are a unique line independent of the initial state of sand, and the critical stress ratio \(M\) (=\(q/p^{\prime}\)) is constant, which is also independent of the initial state [34; 35; 36; 37; 38]. On the contrary, the experimental results for aeolian sand show that the CSL in the plane of \(q\)-\(p^{\prime}\) and \(e\)-\(lnp^{\prime}\) are not unique but dependent on the initial void ratio, that is, \(M\) is not a constant but dependent on the initial void ratio. The unique physical and mechanical behaviours of aeolian sand have attracted our attention, thus a series of experimental tests have been conducted. At the same time, it takes the construction of the Wuma Highway as the background which is located at the southern edge of the Tengger Desert. With the different relative densities and confining pressure, the research throws emphasis on numerous factors that are capable of influencing the shear behaviour of aeolian sand by the triaxial test. Specifically, the reason why aeolian sand shows special critical state behaviour will be discussed. Two empirical formulas will be established to describe the strength behaviours of aeolian sand considering relative density and confining pressure. This research can not only provide basis parameters for the establishment of a constitutive model for aeolian sand, but also provide a reference for the design of geotechnical construction in desert areas.