# Experimental Study on Mechanical Properties of Highway
## 3 Experiment Results and Analysis
### Effect of Confining Pressure on Mechanical Properties  
Figure 16 shows the stress-strain curves of the thawed subgrade soil under different peripheral pressures (50 kPa, 100 kPa, 150 kPa) with a moisture content of 10%, a freezing temperature of \(-10\)\({}^{\circ}\)C, and different peripheral pressures (50 kPa, 100 kPa, and 150 kPa) after one freezing and thawing cycle. From the Figure, it can be seen that with the increase of the peripheral pressure, the stress-strain relationship curves of the roadbed soil have the same basic morphology, which are hardened curves. Additionally, with the increase of the axial strain, the axial bias stress also gradually increases, and there is no peak bias stress. Moreover, with the increase of the peripheral pressure, the strength of the roadbed soil increases more, indicating that the influence of the peripheral pressure is more pronounced. The influence of the perimeter pressure on the destructive stress and modulus of elasticity of the roadbed soil is shown in Figure 17. It can be observed that as the perimeter pressure increases, the destructive stress of the roadbed soil exhibits an approximate linear growth trend. When the perimeter pressure increases from 50 kPa to 150 kPa, the destructive stress of the subgrade soil increases from 194.7 kPa to 367.7 kPa, which represents an increase of 173 kPa, corresponding to a growth rate of approximately 88.8%. Similarly, the modulus of elasticity of the roadbed soil also increases with the increase in the perimeter pressure. Specifically, when the perimeter pressure increases from 50 kPa to 150 kPa, the modulus of elasticity of the roadbed soil increases from 0.366 MPa to 0.931 MPa. This indicates an increase of 0.564 MPa, or about 154.1%. Figure 16: Influence of confining pressure on stress–strain relations. \begin{table}
\begin{tabular}{c c} \hline \hline
**Moisture Content (\%)** & \(\mathbf{R_{f}}\) \\ \hline
6 & 0.83039 \\
8 & 0.89376 \\
10 & 0.90803 \\
12 & 0.90796 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Damage ratio of soil under different water content. From the analysis of the above test results, it can be concluded that circumferential pressure has a significant influence on the destructive stress and modulus of elasticity of the roadbed soil. This is because the freezing and thawing effect causes an increase in the internal pore volume of the soil, leading to soil loosening. Consequently, with an increase in perimeter pressure, the roadbed soil becomes compacted and the pore space reduces, resulting in an increase in the strength of the soil structure. Furthermore, the increase in peripheral pressure enhances the degree of consolidation of the subgrade soil, thereby improving the roadbed soil's resistance to deformation. Figure 18 is the relationship curve between \(\varepsilon_{1}/(\sigma_{1}-\sigma_{3})\) and \(\varepsilon_{1}\) under different water content conditions. The values of test parameters a and b in the model can be obtained by linear fitting of each curve in Figure 18, as shown in Table 10. It can be seen from the Table that the determination coefficient \(\mathbb{R}^{2}>0.99\), and the fitting degree is high. Figure 17: Confining pressure—elasticity modulus relation diagram. When calculating 1/a and 1/b, the initial tangent modulus, ultimate deviatoric stress versus the enclosing pressure are obtained, as shown in Figure 19. From the Figure, it can be seen that as the enclosing pressure grows from 50 kPa to 100 kPa, the parameter 1/a increased by 56.0% and the parameter 1/b increased by 50.2%. As the enclosing pressure grows from 100 kPa to 150 kPa, the parameter 1/a increased by 38.2% and the parameter 1/b increased by 26.4%. The above results indicate that the initial tangent modulus of the soil increases approximately linearly with the increase of the confining pressure, while the ultimate deviatoric stress of the soil increases gradually and its growth rate slows down.