## 2 Uniaxial Compression Test on Earth Materials  
### Selection and Preparation of Specimens  
A reasonable selection of earth materials is a prerequisite for ensuring the good mechanical properties of the earth structure. The soil used in this experiment was obtained from the region of Shihezi in China, which was traditionally used to make clay bricks in the past. The soil was passed through a 2-mm standard sieve to remove the debris and impurities incorporated in it. The main components of the test soil samples were detected using an X-ray fluorescence analyzer of the S8 ITGER series (Figure 1a). The main components of the soil sample are shown in Table 1. To analyze the mineral composition in the earth materials, a Smartlab 9 kw X-ray diffractometer from RIGAKU was used to test the soil samples. The test apparatus is shown in Figure 1b. The test conditions were Cu K\(\alpha\) radiation, operated at 40 kV-150 mA, step size = 0.02\({}^{\circ}\) and a scan range 20 from 3\({}^{\circ}\) to 80\({}^{\circ}\). Before testing, the test soil sample was crushed and passed through a 200-mesh sieve, then poured into the sample tray, and the sample surface was treated with frosted glass to ensure a smooth surface. The X-ray diffraction pattern of the tested soil is shown in Figure 2.  
The soil sample Atterberg limit used was tested with reference to the Chinese standard \"Standard for Geotechnical Test Methods\" (22) (GB/T 50123-2019). The basic physical properties, such as maximum dry density and optimum water content, were measured using the light compaction test (22), and the results are shown in Table 2. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Chemical Compositions** & **SiO2** & **Al2O3** & **CaO** & **Fe2O3** & **MgO** & **K2O** & **Na2O** & **TiO2** & **P2O5** & **SO3** \\ \hline Content (\%) & 59.49 & 17.4 & 7.58 & 5.393 & 3.9 & 2.89 & 1.79 & 0.678 & 0.346 & 0.191 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main components of soil. Figure 1: Testing instruments: (**a**) X-ray fluorescence analyzer; (**b**) X-ray diffractometer. Figure 3 shows the particle size distribution curves of the earth materials used in this experiment and in the related literature [1,14,19,23,24,25,26,27,28]. The obtained curves were also compared with the particle size range recommended by CRATerre (Centre de Recherche en Architecture en Terre) [29] for making compacted soil specimens. It can be seen that the particle size distribution curves of the earth materials used in this experiment and in the related literature are basically between the upper and lower limits of the particle sizes given by them, and no correction of the soil particle sizes is required. According to ASTM D2487 [30], the composition of the soil was 19% clay particles (<5 \(\upmu\)m), 39% powder particles (5-75 \(\upmu\)m), and 42% sand (75-4500 \(\upmu\)m). The total amount of clay particles and powder particles is 58% > 50%, which is a fine-grained soil. Figure 4 shows a plastic diagram of the soil used in this test and related literature [1,14,19,23,26,27,28]. In Figure 4, it can be seen that the soil used in this test has a liquid limit LL = 36.3% < 50% and a plasticity index PI = 12.8 \(\geq\) 11.899, which is a low \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Granulometry**} & \multicolumn{3}{c}{**Atterberg Limits**} & \multicolumn{1}{c}{**Maximum**} & \multicolumn{1}{c}{**Dry Density**} & \multicolumn{1}{c}{**Optimal Water**} \\ \hline
**Clay (\%)** & **Silt (\%)** & **Sand (\%)** & **LL (\%)** & **PL (\%)** & **PI (\%)** & **PI (\%)** & **(g\(\cdot\)cm\({}^{-3}\))** & **(g\(\cdot\)cm\({}^{-3}\))** & **Content (\%)** \\
**d \(<\) 5 \(\upmu\)m** & **5 \(\upmu\)m** & **5 \(\upmu\)m** & **4 \(\upmu\)m** & **36.3** & 23.5 & 12.8 & 2.04 & 1.66 & 23 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Basic physical properties of earth materials. Figure 3: Grain size distribution curve of soil [1,14,19,23,24,25,26,27,28]. Figure 2: X-ray diffraction pattern of the earth materials.