## 5 Conclusions  
In this paper, the settlement, axial force, shaft friction, and pile tip force of adjacent pile bases were researched based on model tests. The main conclusions are shown below.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & & & & & \\ \hline Time/h & 0 & 4 & 8 & 12 & 16 & 20 \\ \hline PTF/kN & 0.159 & 0.170 & 0.202 & 0.348 & 0.484 & 0.585 \\ \hline \hline \end{tabular}
\end{table}
Table 6: The mean values of pile tip force of 4 single piles with the increase in time.  
Figure 15: The changing curves of load sharing ratio of pile tip force with immersion.  
1. The load-settlement curve had an obvious inflection point and can be divided into three stages: initial gradual stage, rapid drop stage, and late gradual stage.
2. The axial force decreased along the depth due to the positive shaft friction. And the bearing type of the pile base would change when the vertical load exceeded the ultimate bearing capacity.
3. The settlement of the pile base would significantly increase after immersion due to the collapsibility of the loess.
4. The axial force at the top of the pile increased along the depth after immersion due to the negative shaft friction, and the position of the neutral point moved down as immersion time increased. The bearing type of the pile base would change after immersion.  
This paper designed model tests of adjacent pile bases through the reasonable similarity parameters of size and material properties. And the results analysis methods in previous research were applied, so the conclusions could reflect the machinal characteristics of the adjacent pile bases. But it also should be noted that the artificial loess used in this research cannot reproduce the structure of natural loess completely, which may cause errors in the test results. Meanwhile, the settlements of the soil between the adjacent pile bases were not measured, which is a deficiency of the research. Future work may focus on the following aspects: exploration of artificial loess which can simulate the structure of natural loess better; field tests of adjacent pile bases, including static load and vibration load tests; numerical simulation of adjacent pile bases; the theoretical analysis of the bearing mechanism of the pile bases.  
All authors contributed to the conception and design of this research. Material preparation, test implementation, data collection and analysis were performed by [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON]. Supervision was performed by [PERSON] The first draft of the manuscript was written by [PERSON] and all authors commented on previous versions of the manuscript. The revisions of the manuscript were performed by [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China (Grant No. 51879212), Key Research and Development Program of Shaanxi Province in China (Grant No. 2019 KWZ-09), and Qin Chuangyuan Scientist-Engineer Team Construction Project of Shaanxi Province in China (Grant No. 2023 KXJ-178).  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
Author [PERSON] was employed by the company Guangzhou Metro Design & Research Institute Co., Ltd. The remaining authors declare that the re-search was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.