## 4 Results and Discussion
### Ucs  
The experimental study on the mechanical characteristics of expansive soil were carried out in high temperature-drying (50 \({}^{\circ}\)C-10%) and high temperature-humidity (50 \({}^{\circ}\)C-70%) conditions. Figure 9 shows the mechanical properties of expansive soil in different dehydration environments varying with dehydrated time. Figure 10 shows the variation of UCS of expensive soil with dehydration time. Seen from Figure 9, both the environmental condition and dehydration duration have significant effects on mechanical properties of expansive soil. In the high temperature dehydration environment, the axial stress of its deformation and failure is very large, and the failure mode is no longer just creep mode [24]. The detailed changes are as follows. According to Figure 9a, in the high temperature drying environment, the failure mode of the expansive soil sample gradually changed from creep failure to brittle failure with the process of dehydration. In the initial state, the expansive soil sample began to produce obvious swelling deformation when the axial strain was 6.9%, and the axial stress of the sample was 20.0 kpa, presenting typical creep failure characteristics. In this environment, a mechanical experiment was carried out on the soil sample after one day of dehydration. When the axial strain was 4.2%, the sample began to produce obvious bulging deformation, and the axial stress of the soil sample was 401.2 kpa. After 7 days of dehydration, the expansive soil sample failed at the axial strain of 2.1%, forming an obvious shear plane, and the axial stress of the sample was 3096.7 kpa. After 15 days of dehydration, shear failure occurred at the axial strain of 1.5%, and the axial stress of soil sample was 2886.6 kpa. As shown in Figure 9b, the failure mode of expansive soil samples gradually changed from creep failure mode to brittle failure mode with the process of dehydration in high temperature and humidity environment. In the initial state, the swelling deformation of the expansive soil sample began to occur when the axial strain was 6.9%, and the axial stress of the sample was 20.0 kpa, showing typical creep failure characteristics. Mechanical experiments were carried out after one day dehydration in this environment. The samples began to produce obvious bulging deformation at the axial strain of 4.5%, and the axial stress of the soil sample was 150.6 kpa. After 7 days of dehydration, shear failure occurred when the axial strain was 3.8%, and the axial stress of the sample was 4417 kpa. After 26 days of dehydration, brittle shear failure occurred when the axial strain was 2.6%, and the axial stress was 5660.1 kpa. Figure 10 shows that the UCS of expansive soil samples varies with dehydration time under different environmental conditions. In the high temperature dehydration environment, the UCS is much larger compared to that of samples under other conditions [2; 3]. Under the high temperature and dry (50 \({}^{\circ}\)C-10%) environment, the UCS of the sample increased first, then decreased, and finally reached a stable trend with the process of dehydration. The maximum UCS of soil samples in the initial state was 27.8 kpa. With  
Figure 9: Stress-strain curves of expansive soil varying with dehydration time under different environment conditions (**a**) 50 \({}^{\circ}\)C-10%, (**b**) 50 \({}^{\circ}\)C-70%. the dehydration process, the maximum UCS of soil sample was 3277 kpa after 5 days of dehydration. After 10 days of dehydration, the UCS of the soil sample decreased to 2546 kpa. The UCS was 2886.6 kpa until the mass of soil sample reached stability after 15 days of dehydration. Under high temperature and humidity (50 \({}^{\circ}\)C-70%) environment, the UCS of the sample increased first and then reached the dynamic equilibrium with the dehydration process. In the initial state, the maximum UCS of the soil sample was 27.8 kpa. When the soil was dehydrated for 15 days, the maximum UCS of the sample reached 5921 kpa. Thereafter, the UCS of the sample changed little.