## 3 Experimental Results and Analysis
### Effect of FT Cycles and Confining Pressure on the Mechanical Properties of Specimens
After six cycles, it ranges from 13.31 kPa (w = 11.6%) to 27.25 kPa (w = 7.6%), averaging 20.85 kPa. After 10 cycles, it ranges from 12.77 kPa (w = 11.6%) to 22.43 kPa (w = 7.6%), averaging 17.88 kPa. After 15 cycles, it ranges from 9.08 kPa (w = 11.6%) to 20.99 kPa (w = 7.6%), averaging 14.80 kPa. Over the course of 0 to 15 cycles, the cohesion decreases by 38.12% to 54.98%. It is evident that the increase in FT cycles significantly degrades the cohesion of the soil, with the degradation weakening as the number of cycles increases and stabilizing after 10 cycles. The internal friction angle behaves similarly. When the number of FT cycles is 0, it ranges from 23.49\({}^{\circ}\) (w = 11.6%) to 25.34\({}^{\circ}\) (w = 7.6%), averaging 24.46\({}^{\circ}\). After one cycle, it ranges from 21.30\({}^{\circ}\) (w = 11.6%) to 23.53\({}^{\circ}\) (w = 7.6%), averaging 22.52\({}^{\circ}\). After three cycles, it ranges from 20.33\({}^{\circ}\) (w = 11.6%) to 22.20\({}^{\circ}\) (w = 7.6%), averaging 21.10\({}^{\circ}\). After six cycles, it ranges from 18.43\({}^{\circ}\) (w = 11.6%) to 20.15\({}^{\circ}\) (w = 7.6%), averaging 19.45\({}^{\circ}\). After 10 cycles, it ranges from 16.00\({}^{\circ}\) (w = 11.6%) to 19.66\({}^{\circ}\) (w = 7.6%), averaging 17.27\({}^{\circ}\). After 15 cycles, it ranges from 16.05\({}^{\circ}\) (w = 11.6%) to 18.02\({}^{\circ}\) (w = 7.6%), averaging 17.04\({}^{\circ}\). Over the course of 0 to 15 cycles, the internal friction angle decreases by 28.89% to 31.67%. The internal friction angle also gradually decreases with an increasing number of cycles, with the rate of decrease slowing after 10 cycles. The deterioration of cohesion is partly due to the phase change of pore water during freezing, which increases the pore volume and particle spacing, weakening inter-particle interlocking. Additionally, FT cycles cause some coarse particles to break and fine particles to aggregate, reducing the bonding and interlocking between particles. Similarly, the decrease in internal friction angle is caused by changes in particle gradation, which reduce the soil's heterogeneity and lower the friction coefficient [4]. The weakening of inter-particle interlocking also contributes to the decrease in the internal friction angle. After 10 FT cycles,  
Figure 8: The relationship between cohesion (c), internal friction angle (\(\varphi\)), and the number of FT cycles. (**a**) Cohesion c and (**b**) the internal friction angle \(\varphi\). Figure 9 presents the shear behavior of coarse-grained soil samples from the southeastern Xizang region under different confining pressures (\(\sigma_{3}\)) and water contents (w) of 7.6%, 9.6%, and 11.6%, without undergoing FT cycles. The degree of strain softening  
Figure 11: Stress–strain curves of samples with different water contents under various confining pressures (FT = 15). (**a**) \(\sigma_{3}\) = 50 kPa, (**b**) \(\sigma_{3}\) = 100 kPa, (**c**) \(\sigma_{3}\) = 150 kPa, and (**d**) \(\sigma_{3}\) = 200 kPa. Figure 4.0 Stress–strain curves of samples with different water contents under different confining pressures (FT = 6). (**a**) \(\sigma_{3}\) = 50 kPa, (**b**) \(\sigma_{3}\) = 100 kPa, (**c**) \(\sigma_{3}\) = 150 kPa, and (**d**) \(\sigma_{3}\) = 200 kPa. increases with water content and decreases with confining pressure. Under the same testing conditions, as the water content increases from 7.6% to 11.6%, the average strain softening degree progressively increases, reaching 8.03% (w = 7.6%), 10.80% (w = 9.6%), and 15.95% (w = 11.6%). Conversely, as the confining pressure rises from 50 kPa to 200 kPa, the average strain softening degree decreases, with values of 17.95% (\(\sigma_{3}\) = 50 kPa), 11.67% (\(\sigma_{3}\) = 100 kPa), 9.35% (\(\sigma_{3}\) = 150 kPa), and 7.39% (\(\sigma_{3}\) = 200 kPa). Figures 10 and 11 illustrate the shear behavior of the same samples after undergoing six and fifteen FT cycles, respectively.