# Numerical Analysis of the Installation Process of Screw Piles Based on the FEM-SPH Coupling Method
## 4 Numerical Results
### Influence of Pile Structure Parameters on Soil Stress  
During the installation process, due to the squeezing and shearing of the screw pile on the surrounding soil, the soil stress variations around the screw pile can be observed significantly. At the end of the installation of the screw pile, the state of soil shear stresses around the pile is shown in Figure 19. For different screw piles, there is a consistency in the variation range of the surrounding soil stress, and the stress area is approximately symmetrical. The maximum soil stress values around all different piles are 2.309 \(\times\) 10\({}^{5}\) Pa, and the areas of soil stress variation are all located near the screw piles. Figure 18: Soil pressure contour caused by the installation of the screw pile: (**a**) NT2, (**b**) NT3, (**c**) NT4 and (**d**) NT5. As is shown in Figure 19, for different screw piles, all the variation areas of soil stress develop into different shapes at different depths, which is related to the soil failure mechanism caused by the installation of the screw pile. For the shallow soil, the range of stress variation develops into a funnel shape, and the size of this zone is related to the pile's structural parameters. It can be seen that for the four screw piles, the variation range of shallow soil stress around NT4 is almost equal to that of NT5 (Figure 19c,d), while the stress variation range of NT3 is greater than that of NT2 (Figure 19a,b), but none of the stress variations extend to the soil boundary. The damage to shallow soils is mainly caused by HFM, indicating that the range of stress variation by HFM on the shallow soil is only related to the pile diameter, and it is irrelevant to the spiral pitch. The larger the pile diameter, the greater the range of stress variation in the shallow soil. For the middle soil, the range of stress variation corresponds to the inter-helical profile, which is approximated as the size of the screw diameter. It can be found from Figure 19c,d that the stress range of NT4 is larger than that of NT5, indicating that the variation in spiral pitch will change the stress variation range of the middle soil caused by CSFM, which will increase with the decrease in spiral pitch. This is mainly related to the helical blade's shearing action. For NT2 and NT3 (Figure 19a,b), the soil stress range of NT2 is smaller than that of NT3. The pile diameters of the two screw piles are different, but all other parameters are the same, indicating that the variation in pile diameter will change the stress variation range of the middle soil caused by CSFM, which will increase with the increase in pile diameter. This is related to the squeezing effect of the screw pile. As is shown in Figure 19, it can be seen that for the range of stress variation at different depths, the stress range in the shallow soil is greater than that in the middle soil, indicating that HFM has a stronger effect on the soil stress around the screw pile than that of CSFM during the installation process. For the deep soil, as is shown in Figure 19, it can be seen that for the different screw piles, the soil stress variation around the pile develops into a circular region, the size of which is approximately twice the pile diameter. As is presented in Figure 19, the circular variation range of deep soil stress around NT4 is almost equal to that of NT5, while NT3 has a greater range of stress variation than NT2, indicating that the stress region around the pile in the deep soil is related to the pile diameter and unrelated to the spiral pitch. This phenomenon is mainly related to the resistance of the pile tip during the installation process. For the range of soil stress variation around the pile tip, it can reflect the magnitude of the tip resistance. During the installation process, the tip resistance of is usually correlated with the taper angle of the pile tip.