# Influence of Perforated Soils on Installation of New Piles
## 4 Analysis Results and Discussion  
### Influence of Soil with Difference in Mechanical Properties  
The study assumes a soil with one (homogeneous) mechanical property and a soil boundary with two (heterogeneous) mechanical properties. During the installation of the new pile on that soil, the behavior of the new pile is verified. Here, in the homogeneous soil, two cases are assumed: a homogeneous soil with an N value of 50 (Case-1) and a homogeneous soil with an N value of five (Case-2). Furthermore, it is assumed that soils with N values of 50 and five are halved in the heterogeneous soil (Case-3). Figure 6 corresponds to Case-3 and shows the position where a new pile is installed at the boundary between two types of soil with different mechanical properties. For Case-1 and Case-2, there is no boundary between the two types of soil, but the new pile is installed at the same position as that of Case-3. The load acting on the pile head of the new pile is 200 N/mm\({}^{2}\).  
Figure 7 compares the displacements of the soil in the \(x\)-axis direction in Case-1, Case-2, and Case-3. The new pile cast in Case-3 tends to lean toward the soil with an N value of five (positive \(x\)-axis direction) compared to Case-1 and Case-2. Focusing on the deformed shape of the new pile, it can be confirmed that the warp rises to the soil side (negative direction in the \(x\)-axis direction) with an N value of 50, approximately 10 m from the tip of the pile. Figure 8 shows the displacements in the \(x\)-axis direction as a result of Case-3. It also shows, for reference, the assumption that the new pile was installed straight, without deformation. Figures 9 and 10 show the stress in the \(x\)-axis direction inside the soil. Figure 9 is a top view of the analysis model, and Figure 10 is a cross-section of the analysis model cut parallel to the \(x\)-axis. Most of the new pile is inclined toward an N value of five, that is, the soft soil side. On the soil surface, the stress acts in the negative direction in the \(x\)-axis only on the soil around the pile, while the stress inside the soil with an N value of 50 is working on the positive direction in the \(x\)-axis.  
Figure 6: Top view of installing position of newly built pile foundation.  
Figure 7: Comparison of displacements of ground in \(x\)-axis direction in Case-1, Case-2, and Case-3.  
Figure 8: Displacements in \(x\)-axis direction as a result of Case-3, as well as when assuming that the new pile was installed straight, without deformation.  
Figure 10: Side view of stress distribution in \(x\)-axis direction inside ground for Case-3.  
Figure 9: Top view of stress distribution in \(x\)-axis direction inside ground for Case-3.  
From the results obtained from Figures 7-10, it is considered that the stress from the harder soil with an N value of 50 pushes the new pile on the soil surface near the new pile. In addition, it is thought that the stress generated in the warped state of the new pile will return to the original state (the non-warped state). Due to the above two factors, the stress acting on the soil surface around the new pile is assumed to act in the opposite direction to the direction in which the new pile is inclined.  
The displacement in the \(y\)-axis direction of the new pile cast at the boundary between the two types of soil with different mechanical properties was 0.1 mm maximum. From this, it is thought that there is no inclination in the \(y\)-axis direction.