# 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  
In order to study the deformation characteristics of soil environment temperature on zinc-contaminated red clay, four different temperature red clay stress-strain curves were selected under the conditions of zinc pollution concentration of 0% and 0.5% and confining pressure of 300 kPa and 400 kPa, as shown in Figure 2.  
Figure 1: Temperature-controlled SLB-1 type stress–strain controlled triaxial shear penetration tester. According to the classification of mechanical properties of the soil stress-strain relationship, there are usually three types of strain hardening type, strain softening type, and ideal elastic-plastic type. As can be judged from the change of curves in Figure 2, the stress-strain relationship of red clay at different temperatures is of the strain-hardening type. As axial strain increases, the corresponding principal stress difference demonstrates a linear increase followed by a gradual increase. Initially, the deformation modulus of the red clay increases sharply; then, it decreases rapidly and then slowly with the increase of the axial strain. In Figure 2a, the elastic limits appear at \(\varepsilon=2.5\%\), \(2\%\), \(2.5\%\), and \(2.5\%\) for the soils at each temperature condition with the increase of ambient temperature; and the elastic limits are 189.7 kPa, 187.1 kPa, 184.1 kPa, and 219.5 kPa, respectively. In Figure 2b, with the increase of ambient temperature, the elastic limits appear at \(\varepsilon=2\%\), \(2\%\), \(1\%\), and \(1\%\) for the soils at each temperature condition, and the elastic limits are 155.2 kPa, 235.4 kPa, 253.4 kPa, and 257.3 kPa, respectively. This indicates that the \(\varepsilon\) corresponding to the elastic limit of uncontaminated red clay is basically constant with increasing temperature, while the \(\varepsilon\) corresponding to the elastic limit of zinc-contaminated red clay is gradually decreasing. Meanwhile, the elastic limit of uncontaminated red clay showed an overall decreasing trend with increasing temperature, while the elastic limit of zinc-contaminated red clay showed an overall increasing trend with increasing temperature. In Figure 2a, it can be seen that when \(\varepsilon=15\%\), the stress in the uncontaminated red clay increases from 295.3 kPa to 353.8 kPa as the temperature increases from 8.3 \({}^{\circ}\)C to 40 \({}^{\circ}\)C, and the soil stresses at each temperature increase by 10.13%, 12.06%, and 19.81%, respectively; while in Figure 2b, the stress of red clay with 0.5% Zn ion concentration increased from 366.8 kPa to 463.7 kPa, and the soil stresses at each temperature increased by 13.25%, 17.91%, and 26.42%, respectively. It indicates that the principal stress difference corresponding to the same axial strain location basically increases with increasing temperature when the zinc ion concentration and the surrounding pressure in the red clay are the same. This suggests that temperature can greatly influence the mechanical strength of Zn-contaminated red clay. The reason is that as the ambient temperature of the soil rises, the red clay soil in the consolidation stage converts more bonded water into free water and discharges it from the soil due to thermal expansion and contraction. The contact between soil particles is closer, which enhances the ability of the soil to resist external shear damage. Meanwhile, the red clay soil in the undrained shear stage will make the movement of residual water more  
Figure 2: Stress–strain curves of red clay under different temperature conditions. **(a)** The zinc ion concentration is 0% and the confining pressure is 300 kPa; **(b)** The zinc ion concentration is 0.5% and the confining pressure is 400 kPa. active due to thermal expansion and contraction. The moisture is more easily dispersed uniformly inside the soil body, and bears part of the external damage force through the super-pore water pressure.