## 2 Experimental Study
### Soil Pressure Pattern  
The failure mechanisms of the soil around the pile are closely related to the interaction between the pile and the soil [31]. To investigate the variation of lateral stresses in the soil during the loading process, lateral stresses at different depths and distances from the pile axis were measured at lateral displacements of 15 mm, 30 mm, 45 mm, and 60 mm from the loading point. The lateral stress values were plotted against depth to study the stress variation in the soil at different locations and depths during the loading process [32].  
Figure 7 illustrates the lateral stresses of the soil at four different loading stages during the loading process. The lateral distance from the pile axis is represented on the \(x\)-axis, while the lateral stress is represented on the \(y\)-axis. Different colors of the curves indicate different depths. The position of 0 mm represents the pile core, and the position of 20 mm represents the pile shaft. Distances greater than 20 mm from the pile axis indicate the soil outside the pile. The analysis reveals that the stress in the pile core soil is higher at the top and lower at the bottom under the same load conditions. The stress in the middle portion of the pile core remains consistently high, while the stress at the pile base remains nearly unchanged. This indicates that during the loading process, the upper part of the pile experiences bending deformation, resulting in higher stress in the upper pile core due to compression from the pile shaft. On the other hand, the lower part of the pile undergoes smaller deformation due to deeper embedment, resulting in lower stress in the middle and lower portions of the surrounding soil. The lateral stresses in the soil near the pile shaft exhibit a higher value at the bottom and a lower value at the top. After a lateral displacement of 15 mm, the stress at the pile base remains almost constant, indicating that the soil at the pile base has already yielded. However, the lateral stresses in the surface soil do not show significant yielding as the displacement increases. This is because as the displacement at the top of the pile increases, the internal soil experiences significant disturbance and damage, following the movement of the pile. The soil located 35 mm away from the pile axis and at the lower portion of the pile base can be considered as representing the soil at a greater distance from the actual pile foundation. During the loading process, the stress variation in this part of the soil is not significant, which is consistent with the actual conditions.  
Figure 7: Soil lateral stress: (**a**) soil lateral stress at a lateral displacement of 15 mm, (**b**) soil lateral stress at a lateral displacement of 30 mm, (**c**) soil lateral stress at a lateral displacement of 45 mm, (**d**) soil lateral stress at a lateral displacement of 60 mm.  
At the same position and loading stage in the soil, the area with the greatest variation in lateral stress with depth is located at a distance of 22 cm from the pile axis. This area represents the soil surrounding the pile foundation that is most affected by the presence of the cellular structure of the pile. On the other hand, the soil at the pile core and slightly farther from the pile base, towards the outer side, undergoes comparatively smaller changes in lateral stress. Meanwhile, the soil pressure near the steel test pit is approximately 0.5 MPa and remains almost unchanged, suggesting that the lateral load-bearing capacity of the GPF is not affected by the boundary.