# Study on Vertical Uplift Resistance Characteristics of Pre-Drilled Planted Piles in Boulder Strata
## 5 Calculation Results and Analysis
### Soil Displacement Field Analysis  
Figures 8 and 9 show the displacement cloud map of the soil and the force chain diagram of soil particles under the action of ultimate bearing capacity. In the figure, X and Y represent the horizontal and vertical distances from the center of the pile head, respectively, both normalized by the diameter D of the core pile.  
Under the action of ultimate load, the influence of the planted pile in Condition 1 on the soil in the Y direction is not significant; however, in the X direction, the range of soil influence is approximately from 0D to 4D, with the displacement field distribution presenting an inverted triangular shape. The soil displacement decreases gradually in the horizontal direction away from the center of the pile, with the maximum displacement  
Figure 8: Displacement contour map and particle force chain diagram of soil around planted pile under Condition 1: (**a**) experimental displacement contour map of soil; (**b**) displacement map of numerical simulation; (**c**) particle force chain diagram of numerical simulation.  
Figure 9: Displacement contour map and particle force chain diagram of soil around planted pile under Condition 2: (**a**) experimental displacement contour map of soil; (**b**) displacement map of numerical simulation; (**c**) particle force chain diagram of numerical simulation.  
occurring at the pile head and decreasing progressively along the pile depth. For Condition 2, the range of influence on the soil in the Y direction is primarily within the length of the pile shaft, approximately 10D, whereas in the X direction, the influence range is about twice that of Condition 1, reaching 8D. This is because the boulder increases the contact area between the pile and the soil, resulting in greater compression between the pile and the soil, which amplifies the horizontal displacement component of the soil above boulder and extends the influence range of the pile tip on the surrounding soil. Due to the shallow burial depth of the boulder, the sliding failure surface of the pile forms earlier, resulting in the largest impact range on the soil in the X direction at the ground surface. The displacement distribution of the soil below the boulder tends to align with that of piles without boulders. The force chain diagram of the pile shows that the strong force chain area in Condition 1 appears deep within the pile, where the side friction resistance at greater depths fully exerts its effect under the ultimate load. In Condition 2, the strong force chain area is in the soil particles above the boulder and those in contact with the pile shaft, confirming that during the uplift process, boulders can provide more side friction resistance and uplift resistance, effectively counteracting the uplift load.  
This phenomenon further confirms the positive influence of the boulder on the mechanical performance of the pile, particularly in enhancing uplift resistance and optimizing load transfer mechanisms. It is also worth noting that the presence of the boulder increases the bearing capacity of the pile and correspondingly expands its influence on the surrounding soil. Therefore, when the cross-sectional area of the boulder is approximately four times that of the pile and it is in the middle of the pile, attention should be paid to the impact of the pile on other piles in engineering practice, with a recommended spacing greater than 8D.