# Triaxial Experimental Study of Zinc Contaminated Red Clay under Different Temperature Conditions
## 2 Materials and Methods
### Test Preparation  
The red clay retrieved from a building pit in Lingui District was air-dried, removed from debris, crushed, and sieved through a 2 mm soil sieve to be utilized as a backup soil for the test. The amount of distilled water required for soil preparation was calculated by the water content of the original red clay, the target value of dry density of the contaminated red clay (1.4 g/cm\({}^{3}\)), the target water content (30%), and other parameters; then, the amount of distilled water required for soil preparation was calculated according to the doping of zinc ions of 0%, 0.05%, 0.1%, 0.2%, and 0.5% (the doping of zinc ions is the mass ratio of zinc ions to dry soil, and the doping amount in this test was determined by [PERSON] et al. in the contaminated red clay). The required Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O mass was calculated based on the desired Zn ion concentration [38; 39] and the actual experimental results. Next, the proper amount of Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O solution was prepared according to the mass ratio needed for sample preparation (i.e., the mass ratio of Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O to distilled water), and finally, the Zn(NO\({}_{3}\))\({}_{2}\) solution was sprayed onto the red clay soil and stirred well. After mixing the soil sample, the zinc-contaminated wet soil was sealed in a constant temperature and humidity chamber for 24 h to make it evenly moist and fully react between the substances, then an appropriate amount of soil was taken for remeasurement of moisture content. When the desired moisture content of the test soil sample and the actual moisture content error are acceptable, the hydrostatic method is employed to generate an 80 mm \(\times\) 39.1 mm  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Optimum** & **Maximum Dry** & **Specific Gravity** & **Compression** & **Liquid** & **Plastic Limit** & **Plasticity Index** \\
**Moisture Content/\(\omega\)** & **Density** & **G\({}_{\text{S}}\)** & **Modulus/MPa** & **Limit (W\({}_{\text{U}}\)/\%)** & **(W\({}_{\text{P}}\)/\%)** & **I\({}_{\text{P}}\)** \\ \hline
30.00 & 1.515 & 2.73 & 10.15 & 57.95 & 31.22 & 26.73 \\ \hline \end{tabular}
\end{table}
Table 1: Basic physical indexes of red clay in Lingui area of Guilin.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**[Zn(NO\({}_{3}\))\({}_{2}\): 6H\({}_{2}\)O]** & **pH Value** & **Clarity** & **Water** & **Chloride** & **Sulfate** & **Iron (Fe)** & **Lead (Pb)** & **Sulfide** \\
**Content** & **(50g/L, 25 °C)** & **Test** & **Insoluble Matter** & **(Cl)** & **(SO\({}_{4}\))** & **(SO\({}_{4}\))** & **Does Not** & **Precipitate** \\ \hline \(\geq\)99.0 & \(\geq\)3.5 & qualified & 0.005 & 0.001 & 0.002 & 0.0003 & 0.005 & 0.10 \\ \hline \end{tabular}
\end{table}
Table 2: Technical conditions of zinc nitrate hexahydrate (Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O) (analytical purity) (unit: %).  
triaxial specimen. When specimen preparation is completed, the prepared specimen must be promptly inserted into the triaxial specimen saturator. Then, it is placed in a vacuum saturation cylinder for at least 2 h, after which it is soaked in distilled water for 12 h to make the specimen completely saturated.