# Triaxial Experimental Study of Zinc Contaminated Red Clay under Different Temperature Conditions
## 3 Results and Discussion
#### 3.1.1 Effect of Temperature on Stress-Strain Curves of Zinc-Contaminated Red Clay
1.2 Effect of Contamination Concentration on the Stress-Strain Relationship of Red Clay under Temperature Conditions  
In order to study the deformation characteristics of red clay under the temperature conditions of pollution concentration, the stress-strain curves of red clay with five kinds of zinc pollution concentration under the ambient temperature of 8.3 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, and the surrounding pressure are 300 kPa are selected, as shown in Figure 3.  
Based on the type of soil stress-strain relationship and the change of stress-strain curve in Figure 3, it is possible to conclude that the stress-strain curve of red clay with varying contamination concentrations at the same ambient temperature exhibits strain hardening. During the shearing process, the primary stress difference exhibited a linear increase, followed by a slow increase, as the axial strain increase, while the deformation modulus also showed a trend of rapid increase and then a slow decrease. Comparing the curves in Figure 3, it was discovered that when the ambient temperature and the surrounding pressure of the soil were the same, the principal stress difference corresponding to the same axial strain of the red clay with Zn ion concentration from 0 to 0.05% exhibited an increasing trend, while the principal stress difference corresponding to the same axial strain of the red clay with Zn ion concentration from 0.05% to 0.5% exhibited a decreasing trend, and the degree of decrease was more obvious. In Figure 3a, it can be seen that when \(\varepsilon\) is 15%, the stress in the red clay at 8.3 \({}^{\circ}\)C increased from 295.3 kPa to 369.7 kPa, then decreased to 314.7 kPa as the concentration of zinc ions in the soil increased from 0 to 0.5%, and the stress in the soil at each concentration increased by 25.19%, 18.90%, 13.85%, and 10.66%, respectively. In Figure 3b, with the increase of zinc ion concentration in soil, the stress of red clay at 8.3 \({}^{\circ}\)C first increases from 353.8 kPa to 414.6 kPa and then decreases to 345.3 kPa, and the soil stress at each concentration increases by 17.18%, 14.47%, 10.96%, and \(-\)2.45% respectively. It indicates that the amount of Zn ions in red clay can influence its macroscopic strength via altering the red clay deformation. The reason is that when small amounts of zinc ions are present in red clay, crystalline water is present in the zinc salt produced by the reaction of zinc ions with soil particles. The crystalline water causes the surrounding soil  
Figure 3: Stress–strain curve of red clay with Zn pollution concentration. **(a)** The temperature is 8.3 \({}^{\circ}\)C and the confining pressure is 300 kPa; **(b)** The temperature is 40 \({}^{\circ}\)C and the confining pressure is 300 kPa. particles to have a fitting effect, which in turn causes the local soil particles to aggregate. The denseness of the soil increases, making the soil more resistant to external destructive forces. When large amounts of zinc ions are present in the red clay, the zinc ions react with a large number of soil particles to produce more zinc salts. The bound water in zinc salts can attract to more soil particles and form larger agglomerates of soil particles, which destroys the overall structure of the soil body. At the same time, the reaction of zinc ions with soil particles destroys the cementing material between soil particles and also reduces the attraction between soil particles. Therefore, the macroscopic manifestation is that the ability of the soil body to resist external destructive forces is reduced.