# Shear Behaviour of Aeolian Sand with Different Density and Confining Pressure
## 2 Materials and Methods
### Test Method  
This study used an automatic triaxial testing system with digital data acquisition capabilities. Axial force was controlled by a servo motor, the maximum was 30 kN, and the measurement accuracy was \(\pm\)1% FS (Full Scale). The confining pressure and back pressure were all controlled by hydraulic pressure, the maximum confining pressure was 1.99 MPa, the maximum back pressure was 0.99 MPa, and the control accuracy was \(\pm\)0.5% FS. Tests were performed on the cylindrical specimen of 61.8 mm diameter and 125.0 mm height. In order to keep the density of the specimen consistent within the height range, it was divided into five layers to prepare, and the method of under compaction was used, this method was first proposed by [PERSON] [43] and suggested that the relative density of the upper and lower layers of soil specimens differs by 1%. The specific operation steps were as follows (the test is carried out in a relatively stable environment, such as the temperature is 22-26 \({}^{\circ}\)C, the air humidity is 40-44%):  
1. In the test, the sample mass of the dry sand was divided into five parts and the relative density of the lower layer is 1% lower than that of the upper layer. For example, to prepare a specimen with a relative density of 50%, the relative density of the five layers from bottom to top is 48%, 49%, 50%, 51% and 52%, respectively, as shown in Figure 2a;
2. It needs to bind the latex membrane on the base of the triaxial cell, put the porous stone and filter paper into the latex membrane in turn, and then fix the mould on the base. Then, a vacuum pump was used to draw the mould so that the latex membrane was tightly attached to the inner wall of the mould;
3. Next, sprinkle the divided specimen into the latex membrane, and to use a tool (as shown in Figure 3) to accurately control the height of each layer. Then, the filter paper, porous stone, and loading cap were installed in turn; \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**CD/CU**} & **Relative Density** & **Void Ratio** & **Sand Mass** & **Effective Confining** \\  & \(D_{\text{r}}\) **(\%)** & \(e\) & **(g)** & **Pressure \(e_{\text{3}}\) (kPa)** \\ \hline \multirow{6}{*}{CD/CU} & 10 & 0.875 & 533.8 & \multirow{6}{*}{100/300/600} \\  & 30 & 0.812 & 552.5 & \\ \cline{1-1}  & 50 & 0.748 & 572.7 & \\ \cline{1-1}  & 70 & 0.684 & 594.5 & \\ \cline{1-1}  & 90 & 0.621 & 617.6 & \\ \hline \multirow{6}{*}{CU} & 50 & 0.748 & 572.7 & 50 \\ \cline{1-1}  & 50 & 0.748 & 572.7 & 800 \\ \cline{1-1}  & 50 & 0.748 & 572.7 & 1200 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Test program. After the specimen preparation, a small vacuum was applied to stabilize the specimen and the mould was carefully removed. As shown in Figure 2b. For specimens with different relative densities, the final volume of all the specimens was the same, so the specimen preparation methods with different relative densities would be different. For the loose sand specimen, de-aired water of about 0.8% of the dry sand should be sprayed on its surface after weighing the dry sand, and then the dry rubbing method should be used to make the water uniformly adhere to the surface of sand particles. After that, the long-neck funnel was used to evenly spread it into the latex membrane in layers. For medium-dense sand, the sand was slowly spread into the latex membrane using a long-neck funnel. For dense sand, the sand was directly spread into the latex membrane with a spoon. In order to make each layer of the specimen reach a predetermined height, the outer wall of the mould was evenly tapped with a rubber hammer. Additionally, the total height of the specimen was strictly controlled to be 125 \(\pm\) 1 mm. After the specimen preparation was completed, the back-pressure saturation is carried out. The back pressure and confining pressure were applied in increments of 50 kPa to help the residual gas inside the specimen dissolve in water, while the confining pressure was maintained at 20 kPa higher than the back pressure.