## 6 Discussion
### External Factors and Existing Pile Efficiency  
The pile arrangement, \(L/B\), the eccentricity of load, and soil properties all affect pile settlement according to Equation (4). After the establishment of new piles, the contribution efficiency results of the pile cap on the settlement of the existing piles are shown in Figure 20. The difference between pile head and bottom remains stable with different \(L/B\), and when \(L/B\) is 5:2, the pile cap size has the least influence on existing piles, but at 4:2, the influence already tends to stabilize. The settlement of the existing piles before and after the establishment of new piles shows significant changes in different soil layers, as shown in Figure 21, including the settlement differences between the pile head and bottom. When the \(E\) is too large or too small, the contribution rates differ significantly. When \(E\) < Ea, the establishment of new piles significantly affects the settlement of existing piles, with the pile head and bottom settlement of existing piles reaching 90% and 150.45%, respectively, under the influence of the efficiency of new piles. Figure 22 shows the settlement contribution efficiency of different pile arrangements on the existing piles after the establishment of new piles. The distance between the pile head and bottom in a symmetrical pile distribution is smaller than that in a lateral arrangement. When the load is evenly distributed on the pile cap, the settlement of the existing pile under symmetrical distribution reaches 2.75% and 13.33% at the pile head and bottom, respectively; the settlement reaches 1.10% and 10.26% at the pile head and bottom, respectively, in a lateral arrangement. Figure 19: Relationship between \(\eta\) and \(d_{\text{N}}\). Based on the parameterized results, the contribution of new piles to the settlement response of existing piles can be quantified using the existing pile efficiency method. From Table 3, it can be seen that, when the geometric parameters of new and existing piles are consistent, the influence of soil and load changes on the settlement of the existing piles is significant. Among the load factors, the settlement variation in symmetrical pile distribution is more stable than in lateral pile arrangement. The impact of pile cap changes on the settlement of existing piles is relatively smaller compared to other factors. Sorting the influence effects by settlement degree, the results show that after the installation of new piles, the most significant contribution to the settlement of the existing piles is due to soil  
Figure 21: Relationship between \(\eta\) and \(E\). Figure 22: Relationship between \(\eta\) and load distribution: (**a**) symmetric arrangement; (**b**) lateral arrangement. changes, followed by the load on the pile cap, \(h_{\text{N}}\), \(d_{\text{N}}\), and pile cap \(L/B\). After determining the soil relationship, necessary load eccentricity tests should be conducted in the analysis of mutual influences between new and existing piles. Based on the new pile parameters obtained in this study, it is reasonable to determine the \(h_{\text{N}}\) in the range of 1.0-1.1\(h\) and the \(d_{\text{N}}\) in the range of 1.0-1.2\(d\). However, from the pile head and bottom data of the soil layer, when the soil layer remains a single layer with different \(E\), there is still a certain difference between the pile head and bottom. This difference indicates the role of pile-side friction. Under the same soil layer, the settlement contribution of the existing pile is more significant in soil layers with low \(E\). This study has demonstrated the potential of utilizing existing piles to support new structures while reinforcing them with complementary piles. The numerical model was calibrated using established geotechnical parameters and validated against static load test data, confirming its reliability for settlement analysis.