## 3 Results  
### Triaxial Shear Test  
The stress-strain curves of the modified sulfate saline soil samples after 1 day and 14 days of curing for different confining stresses are shown in Figures 4 and 5. Figures 4 and 5 show that the samples displayed strain-softening behavior. The deviatoric stress of all the samples increased rapidly at a lower axial strain before reaching the peak stress. Then, the deviatoric stress decreased to the residue deviatoric stress. The slope of the stress-strain curves declined gradually with axial strain and finally became zero when the peak deviatoric stress was reached. As the axial strain increased, the slope of the stress-strain curves turned negative. As shown in Figure 4a-c, both the content of CLI and the confining pressure had a significant influence on the stress-strain curves. As the confining pressure increased from 100 kPa to 300 kPa, the samples exhibited a higher deviatoric stress. Compared with the non-modified samples (the content of CLI = 0%), the shear strength of modified samples was effectively improved. As the content of CLI increased from 0% to 12%, the deviatoric stress increased and then decreased. When the content of CLI was 8%, the deviatoric stress reached the maximum. Take the confining pressure of 100 kPa as an example: the peak deviatoric stress of the sample with 8% CLI content was enhanced by about 122.22%, 89.38%, and 70.56 compared to the samples with CLI content of 0%, 4%, and 12%, respectively. Moreover, the slope of the stress-strain curves of the 8% CLI-treated soil before reaching zero was steeper than the others. The stress-strain curves of samples with 4% and 12% CLI showed a similar tendency. Figure 4d shows the effect of CLI content and confining pressure on the secant modulus, in which the secant modulus was defined as the ratio of the peak deviatoric stress to the corresponding axial strain. In general, the secant modulus increased with confining pressure. The secant modulus increased as the content of CLI increased from 0 to 8%, which showed improvements of about 2-3 folds. As the content of CLI increased to 12%, the secant modulus decreased but was still higher than that of 4% CLI. In Figure 4a-c, the deviatoric stress response of non-modified samples (the content of CLI = 0%) displays slight post-peak softening, while other samples behave in an obvious strain-softening manner. The deviatoric stress shows an obvious increase with confining pressure for the same content of CLI. Similarly, with samples after 1 day of curing, the deviatoric stress of samples after 14 days of curing increased first and then decreased as the content of CLI increased, with the turning point in the content of 8% CLI. Moreover, the slope of the rising phase of the stress-strain curves was the steepest at the 8% content of CLI, indicating that the use of 8% CLI effectively improves the modified soil's ability to resist shearing at the same axial strain. CLI is a natural soil stabilizer, and it needs to take a period of curing time to form bonding with soil particles. Figures 4 and 5 illustrate that the samples cured for a longer time showed higher deviatoric stresses, which was more phenomenal for a higher content of CLI. With the increase in the curing time from 1 day to 14 days, the stress-strain curves of the samples moved upward and toward the left. The axial strain generated to reach the peak deviatoric stress decreased as the curing time increased. As for the samples after 14 days of curing, the peak deviatoric stress was reached with the axial strain \(<\) 5%, which is less than that of the samples after 1 day of curing. The effects of CLI content and confining pressure on the secant modulus are presented in Figure 5d. The secant modulus increased with confining pressure. This could be attributed to the increasing ductile behavior of the modified soil under higher confining pressures.