## 3 Experiments Results and Analysis  
The stress-strain curve obtained from the consolidation undrained test is shown in Figure 2. From the stress-strain curve of deep clay under different water contents, it can be seen that the lower the water content, the greater the compressive strength of the soil. The compression curve of deep clay under four water contents undergoes a linear elastic stage and a nonlinear stage. In the case of low water content, the samples under triaxial confining pressure were all strain softening. The higher the water content, the later the peak point appeared. The soil sample with low water content had a peak point before the strain was 20%, indicating that the curve of deep clay showed a strain-hardening type when the water content gradually increased. At the same time, it can be seen from the figure that the stress-strain curve of deep expansive clay under high confining pressure tended to strain hardening, while low confining pressure showed strain softening.  
Figure 3 illustrates that under the same confining pressure, the growth rate of stress with strain gradually decreased as the freeze-thaw times increased. Meanwhile, the ultimate peak stress also decreased as a result of the freeze-thaw cycles. The initial stress was linearly proportional to the strain during triaxial compression and, then, gradually became a nonlinear relationship because of internal damage. Under different freeze-thaw cycles, the stress-strain curves of triaxial tests all showed strain hardening. Under the three confining pressures, the relationship between compressive strength and number of freeze-thaw  
Figure 2: The stress–strain curve under different moisture contents: (a) \(\omega=\)14%, (b) \(\omega=\) 17%, (c) \(\omega=\) 21%, and (d) \(\omega=\) 24%.  
cycles is shown in the Figure 4. It can be seen that the change rules were basically similar under the three confining pressures. As the number of freeze-thaw cycles increased, the compressive strength decreased significantly. In addition, the compressive strength value decreased significantly when the number of freeze-thaw cycles was small. When the freeze-thaw cycles reached a certain number, the compressive strength remained basically stable, and the change was small. It can be concluded that as the number of freeze-thaw cycles increased, the effect of the freeze-thaw effect on the compressive strength gradually weakened.  
The value of cohesion c and internal friction angle \(\varphi\) are the basic physical index of the triaxial test. The Mohr stress circle envelope was drawn by the limit stress and strain of each freeze-thaw cycle, and the value of the internal friction angle and cohesion was calculated. The Mohr stress circle envelope in several states is shown in Figure 5.  
Figure 4: The relationship between compressive strength and number of freeze–thaw cycles.  
Figure 3: Stress–strain curves under different numbers of freeze–thaw cycles: (**a**) 0 time, (**b**) 3 times, (**c**) 6 times, (**d**) 9 times, and (**e**) 12 times.  
It can be seen from Figure 6 that as the number of freeze-thaw cycles increased, the cohesion tended to decrease, while the internal friction angle tended to increase. For small numbers of freeze-thaw cycles (within six cycles), the freeze-thaw cycles greatly affected both cohesion and the internal friction angle. When the number of freeze-thaw cycles  
Figure 5: The Mohr stress circle under different numbers of freeze–thaw cycles: (**a**) 0 time, (**b**) 3 times, (**c**) 6 times, (**d**) 9 times, and (**e**) 12 times.  
reached roughly nine times, cohesion and the internal friction angle generally stabilized, indicating little impact from freeze-thaw cycles on these shear-strength indices.