# Numerical Analysis of the Installation Process of Screw Piles Based on the FEM-SPH Coupling Method
## 4 Numerical Results
### Analysis of the Installation Process of Screw Piles
#### 4.1.1 Analysis of the Installation Process in the Shallow Soil  
Figure 14 shows the movement displacement curves of the shallow soil particles (0 mm) during the installation of NT3. It can be seen that the soil particles start to move from the pile-soil contact (Time = 0 s) in the radial or axial direction, indicating that the movement of soil particles can only occur under the action of the screw pile during the installation process. For the movement displacement of soil particles, its movement is not unlimited, rather, it will gradually become stable after moving to a certain distance. As is shown in Figure 14a, it can be seen that the displacement curves of the shallow soil particles in the radial direction exist in three states. In the first stage, the displacements of soil particles increase in a straight line with infinite slope in a short period of time. Then, the displacement growth rate becomes relatively slow and eventually reaches a stable value. In the third stage, the displacement of soil particles reaches a stable state, and there will be no change.  
The change in the soil particle's motion is related to this screw pile structure. In the first stage, the movement of soil particles is mainly caused by the rotational squeezing of the pile tip (H1) without spiral blades. Due to the penetration of the screw pile, the displacement of soil particles begins to increase sharply. In the second stage, as is shown in Figure 14a, the radial displacement of the soil particles can also continue to increase when the screw blade contacts the soil (Time = 0.072 s). As is shown in Figure 14a, when the conical pile tip is completely installed (Time = 0.385 s), the motion displacement of soil particles basically reaches the steady state. From the above analysis, it can be seen that the movement of soil particles is mainly caused by the installation of the conical pile tip. This is mainly because the blades of this screw pile are continuous and the spiral pitch is equal; when the pile tip is  
Figure 13: Arrangement of measurement regions.  
completely installed, the blades of the pile body will be installed along the same trajectory, which makes the smallest damage to the soil, so that the motion of soil particles no longer occurs. The movement of soil particles is related to the load transfer between the screw pile and the soil. It can be seen from Figure 14a,b that all soil particles (at positions J, K, L, M and N) with larger motion displacement are located around the screw pile, indicating that the strength of load transfer is related to the distance between soil particles and the screw pile. According to the selected measurement area, it shows that the installation of NT3 has a minimal effect on the soil outside the selected location, further indicating that there is no boundary effect or a small boundary effect of the established soil model.  
The movement displacement curves of soil particles in the axial direction are shown in Figure 14b. It can be found that the movement direction of soil particles is along the  
Figure 14: Displacement of the shallow soil particles in different directions: (**a**) radial and (**b**) axial.  
positive Z-axis, which is opposite to the direction of screw pile installation. This is mainly because the shallow soil is relatively loose and the overburden pressure is small, which makes surface heave occur after the installation of the screw pile. This reflects the heave failure mechanism (HFM) to the shallow soil during the installation of the screw piles.