## 3 Results and Analysis
### Freezing State (\(-5\)\({}^{\circ}\)C) Reinforced Soil Interface Characteristics  
Figure 11 shows the shear displacement-shear stress curve of the interface between the geogrid and coarse-grained soil with different water contents under the freezing state (\(-5\)\({}^{\circ}\)C). The curve is basically the same as the trend of the interface shear displacement-shear stress curve in Section 3.1. There is no obvious brittle shear failure of soil with decreasing freezing temperature [26; 27; 28; 29]. The author considers analyzing from two aspects. First, the soil sample used in this experiment is coarse-grained soil, which is different from the clay or fine-grained soil used by some scholars. Frozen soil is composed of soil particles, unfrozen water, pore ice and air. The unfrozen water content and pore ice play a major role in the shear strength of reinforced soil composites. Compared with frozen clay and frozen fine-grained soil, the soil samples with more coarse-grained content have larger soil skeleton pores, and there is still a considerable amount of unfrozen water in the negative temperature state, which leads to obvious plastic deformation. The pores of fine-grained soil and clay are small. With the increase in compactness, the interaction between the soil and pore ice is obvious. The cementing force of ice enables the surrounding soil to be more compactly bonded together, increasing the cohesion of the soil. Second, the size of the direct shear box used in this experiment is 490 \(\times\) 500 \(\times\) 300 mm (L\(\times\)W\(\times\)H). According to Figure 11, the larger direct shear box does not obviously reflect the difference in the failure mode of the reinforced soil interface at different temperatures. The size effect will affect the shear behavior of the reinforced soil interface, but it decreases with the increase in the size of the test model [30; 31]. Therefore, the temperature variable in the direct shear between the geogrid and coarse-grained interface has little effect on the trend of the stress curve but more on the shear strength. Figure 11: Shear displacement-shear stress curve of the reinforced soil interface under a frozen state (\(-5\)\({}^{\circ}\)C): (a) 2% water content; (b) 4.5% water content; (c) 7% water content. Figure 10: The influence of water content on the peak shear stress of the reinforced soil interface under the nonfreezing state (\(0\)\({}^{\circ}\)C). As shown in Figure 11, in the case of different water contents, the peak shear stress of the reinforced soil interface in the frozen state (\(-5\)\({}^{\circ}\)C) still increases with increasing normal stress. When the normal stress is 40 kPa, 60 kPa and 80 kPa, the peak shear stress corresponding to 2% water content is 31.53 kPa, 39.62 kPa and 45.73 kPa, respectively. The peak shear stress corresponding to a water content of 4.5% is 40.596 kPa, 43.963 kPa and 51.284 kPa. The peak shear stresses corresponding to a water content of 7% are 40.134 kPa, 43.656 kPa and 51.65 kPa. The relationship between the shear strength and the normal stress of the reinforced soil interface under the freezing state (\(-5\)\({}^{\circ}\)C) is shown in Figure 12. When the water content is 2%, the peak shear stress under different normal stresses is still the lowest among the three water contents. However, when the water content is 4.5% and 7%, the peak shear stress under different normal stresses is very close. This is different from the relationship between the shear strength and normal stress of the reinforced soil interface with different water contents in the nonfreezing state (\(0\)\({}^{\circ}\)C). At the same time, according to Figure 13, the influence of the water content on the peak shear stress of the reinforced soil interface under the freezing state (\(-5\)\({}^{\circ}\)C) is also different from that under the nonfreezing state (\(0\)\({}^{\circ}\)C).