## 3 Experimental Results and Analysis
### Effect of FT Cycles and Confining Pressure on the Mechanical Properties of Specimens
The shear strength is plotted based on different FT cycle counts and confining pressures, as shown in Figure 7. Under the same experimental conditions, for samples with different moisture contents, the average shear strength reduction as the FT cycles increase from 0 to 15 is 38.78% (\(\sigma_{3}\) = 50 kPa), 29.75% (\(\sigma_{3}\) = 100 kPa), 30.04% (\(\sigma_{3}\) = 150 kPa), and 28.51% (\(\sigma_{3}\) = 200 kPa), with an average value of 31.77%. It can be seen that with the increase in FT cycles, the shear strength of the soil samples under different confining pressures fluctuates slightly but generally undergoes varying degrees of reduction. The most significant reduction occurs after one FT cycle, with the highest magnitude. As the FT cycles increase, the extent of reduction decreases, and after reaching 10 FT cycles, the reduction begins to stabilize. On the one hand, with the increase in FT cycles, the phase change of water within the soil disrupts its original structure, weakening the soil's resistance to shear failure. On the other hand, the change in particle gradation during the FT process also leads to a decrease in the shear strength of the soil. Under the same experimental conditions, at a moisture content of 7.6%, the shear strength reduction as the confining pressure decreases from 200 kPa to 50 kPa is 61.96% (FT = 0), 62.79% (FT = 1), 64.85% (FT = 3), 65.56% (FT = 6), 65.38% (FT = 10), and 67.21% (FT = 15), with an average of 64.63%. For a moisture content of 9.6%, the shear strength reduction as the confining pressure decreases from 200 kPa to 50 kPa is 66.08% (FT = 0), 66.60% (FT = 1), 68.13% (FT = 3), 68.96% (FT = 6), 67.07% (FT = 10), and 71.05% (FT = 15), with an average of 67.98%. For a moisture content of 11.6%, the shear strength reduction s the confining pressure decreases from 200 kPa to 50 kPa is 66.48% (FT = 0), 67.55% (FT = 1), 72.83% (FT = 3), 69.98% (FT = 6), 69.46% (FT = 10), and 71.39% (FT = 15), with an average of 69.61%. It can be observed that, under the same experimental conditions, the shear strength of the samples with different moisture contents subjected to FT cycles increases with the increase in confining pressure and also increases with the number of FT cycles. This is because, when confining pressure increases, on the one hand, it compacts the samples, increasing the contact between soil particles, reducing the pore spaces and cracks, and tightening interlocking and bonding, thereby strengthening the sample's structure and making failure less likely. On the other hand, the increase in confining pressure also enhances the stress state of the soil particles, increasing the resistance to shear failure behaviors such as particle sliding and overturning, thereby improving the sample's performance in terms of deformation and failure. Based on the results of the FT cycles and confining pressure triaxial tests, [PERSON]'s stress circle and failure envelope for the coarse-grained soil samples from the southeastern  
Figure 7: Variation of shear strength with FT cycles for samples with different moisture contents. (**a**) w = 7.6%, (**b**) w = 9.6%, and (**c**) w = 11.6%. Xizangan region are plotted. The shear strength parameters (c and \(\varphi\) values) of the samples are calculated using the Mohr-Coulomb strength theory and are shown in Figure 8.  
As shown in Figure 8, the cohesion and internal friction angle of coarse-grained soil samples from the southeastern Xizangan region exhibit fluctuations as the number of FT cycles increases from 0 to 15. However, both generally show a gradual decrease, with cohesion decreasing more significantly than the internal friction angle. After 10 FT cycles, these changes begin to stabilize. When the number of FT cycles is 0, the cohesion ranges from 20.17 kPa (w = 11.6%) to 33.92 kPa (w = 7.6%), with an average of 26.53 kPa. After one cycle, it ranges from 17.67 kPa (w = 11.6%) to 29.96 kPa (w = 7.6%), averaging 23.68 kPa. After three cycles, it ranges from 10.95 kPa (w = 11.6%) to 27.57 kPa (w = 7.6%), averaging 20.05 kPa.