## 7 Conclusions  
A series of investigations on the interaction between new piles, soil, and existing piles were conducted to elucidate the settlement behavior of existing piles influenced by new pile installation. The main conclusions are as follows:  
1. The settlement of new piles decreases exponentially with increasing pile spacing (\(d_{\text{N}}\)). As \(d_{\text{N}}\) increases, the settlement in the upper half of both new and adjacent existing piles decreases, while settlement in the lower half increases. The settlement behavior of new and nearby existing piles exhibits significant segmented characteristics as \(d_{\text{N}}\) varies.
2. The installation of new piles induces bidirectional displacement in existing piles. To minimize this impact, it is recommended to select \(d_{\text{N}}\) and \(h_{\text{N}}\) within the ranges of 1.0-1.1\(h\) and 1.0-1.2\(d\), respectively.
3. Compared to symmetrical arrangements, lateral arrangements of new and existing piles demonstrate slightly greater stability in settlement behavior under varying load distributions, making them a preferable design choice for certain loading scenarios.
4. Besides pile height and diameter, pile caps exhibit a size effect on the settlement behavior of new and existing piles. When the cap ratio (\(L/B\)) is approximately 4.2, the settlement difference between new and existing piles tends to stabilize.
5. An existing pile efficiency parameter (\(\eta\)) is introduced, and sensitivity analysis reveals that the most significant factors affecting the settlement behavior are geological properties, load distribution, pile arrangement, \(h_{\text{N}}\), \(d_{\text{N}}\) and \(L/B\), in that order. This parameter provides a practical approach to assessing pile interactions.  
\begin{table}
\begin{tabular}{c c c c c c} \hline  & **File Head** & **Pile Bottom** & **Pile Head** & **Pile Bottom** \\ \hline \multirow{2}{*}{\(d_{\text{N}}\)} & 0.8–1.5\(d\) & 0.8–1.5\(d\) & \multirow{2}{*}{\(h_{\text{N}}\)} & 0.9–1.3\(h\) & 0.9–1.3\(h\) \\ \cline{3-5}  & 4.98–1.84\% & 13.49–16.60\% & & 4.97–7.92\% & 17–0.20\% \\ \hline \multirow{2}{*}{\(L/B\)} & 9:6–15:6 & 9:6–15:6 & \multirow{2}{*}{Soil layer} & 0.56 Ea–1.95 Ea & 0.56 Ea–1.95 Ea \\ \cline{3-5}  & 10.18–0.43\% & 24.14–12.76\% & & 90—32.23 & 150.45—33.88 \\ \hline \multirow{2}{*}{Symmetric arrangement} & 0.5–1 & 0.5–1 & \multirow{2}{*}{Lateral arrangement} & 0.5–1 & 0.5–1 \\ \cline{2-5}  & \(-\)42.67–2.75 & \(-\)43.07–13.33 & & \(-\)60.36–1.10 & \(-\)46.12–10.26 \\ \hline \end{tabular}
\end{table}
Table 3: Contribution values of research factors to settlement response of existing piles.  
**Author Contributions:** J.N.: Conceptualization, Software, Writing--Original draft preparation; Z.Y.: Funding acquisition, Writing--Review and Editing; S.Y.: Validation, Supervision, Software, Investigation, Data analysis; S.C.: Writing--Reviewing and Editing, Resources. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was funded by the China Construction Seventh Engineering Division Co., Ltd. (No. 20220838).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Dataset available upon request from the authors.  
**Acknowledgments:** The authors gratefully acknowledge financial support from the China Scholarship Council.  
**Conflicts of Interest:** Author [PERSON] and [PERSON] were employed by the company Installation Engineering Co., Ltd. and China Construction Seventh Engineering Division, Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The authors declare that this study received funding from the China Construction Seventh Engineering Division Co., Ltd. The funder was not involved in the study design, collection, analysis, interpretation of data, the writing of this article or the decision to submit it for publication.