# A Study on the Vertical Bearing Characteristics of Screw Piles in Permafrost Regions
## 3 Numerical Simulation Analysis
### Analysis of Calculation Results  
Figure 9a indicates the load-settlement curves of the screw pile loaded underground during typical temperatures for February and August. It can be observed that the ultimate bearing capacity of the pile's foundation is less affected by the ground temperature, and the difference between the ultimate bearing capacity of the pile's foundation in February and August is 412 kN. The bearing capacity of the pile's foundation is primarily provided by the pile's side, and the end bearing force accounts for less than 10.1%. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multicolumn{2}{c}{**Modulus of**} & \multirow{2}{*}{**Poisson Ratio**} & \multirow{2}{*}{**Cohesion/kPa**} & \multirow{2}{*}{**Angle of Internal**} & \multirow{2}{*}{**Soil Weight/**} \\  & & & & & **Friction/\({}^{\circ}\)** & **(kN-m\({}^{-3}\))** \\ \hline soil & 340 & 0.40 & 65.4 & 0.8 & 19 \\ pile & 72,000 & 0.33 & & & 22 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Calculation parameters. Figure 8: The influence curves of temperature on the shear characteristics of the contact surface. Figure 7: Calculation model’s boundary conditions and parameters. The axial force on the screw pile during loading is depicted in Figure 9,c. When loading in summer, the axial force on the pile's body changes little in the upper, non-screw section and increases after entering the screw section. The load on the pile's body is primarily borne by the screw section in the permafrost. The seasonally active layer melts in summer and contacts with the steel casing, which is the main reason for the small change in the axial force in this section. When loading in winter and summer, the axial force on the pile's body changes little in the upper, non-screw section and increases after entering the screw section. The load is primarily borne by the thread section in the permafrost. The seasonally active layer produces a frost-jacking force when the soil layer is frost-heaving in winter, and the axial force on the pile's body is different from that in summer, when the top load value is 0. With the increase in the load, the axial force on the pile's body fluctuates periodically in the thread section, which is basically the same as the force that occurs in the summer. Figure 10 indicates the variation curves of the equivalent friction resistance of the pile's side with depth in February and August. Figure 10,b indicate that the lateral friction resistance in the seasonally active layer in August is approximately 25 kPa, and the freezing force between the seasonally active layer and the smooth surface of the steel protective cylinder in winter reaches 95 kPa. The equivalent frictional resistance of the starting and  
Figure 9: Load-settlement curves and axial force curves in August and February. ending thread sections is 2.0-2.5 times that of the middle section. [PERSON]'s [21] test results also revealed a similar phenomenon. The reasons were as follows: the displacement of the thread in the upper part of the pile's thread was larger than that in the middle part of the pile's thread; the bearing capacity of the soil at the bottom of the upper part of the thread was developed quickly; and the load-sharing ratio was high. The lower side of the bottom of the thread section was unaffected by the stress on the other thread sections, and the bearing capacity of the lower part of the soil was higher than that of the middle part. The equivalent plastic strain zone around the pile is depicted in Figure 11. Under summer loading, the soil strength of the seasonally active layer is low, and the equivalent plastic zone at the junction with the frozen soil is concentrated, while the freezing strength of the active-layer soil in the winter is high. Because the contact surface is smooth, the pile-soil freezing force is much smaller than the frozen strength of the soil, resulting in no plastic deformation in that zone.