## 5 Conclusions  
Static load tests were carried out on the uplift and compressive piles respectively. The vertical additional stresses caused by the uplift and compressive piles in the surrounding soil were measured by burying micro earth pressure cells in the soil. After polynomial fitting, the vertical additional stresses immediately adjacent to the pile side were obtained, and a method for calculating the shaft resistance considering the loading and unloading effects was proposed, the following conclusions are obtained after analysis:  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Depth (mm)** & \(\tau_{s0}\) **(kPa)** & \(\tau_{s1d}\) **(kPa)** & \(((\tau_{s1d}-\tau_{s0})/\tau_{s0})\) **(\%)** \\ \hline
300 & 3.37 & 2.61 & \(-\)22.8 \\
600 & 6.74 & 6.05 & \(-\)10.3 \\
900 & 10.12 & 9.49 & \(-\)6.2 \\
1200 & 13.49 & 12.87 & \(-\)4.6 \\ \hline Average value & 8.43 & 7.75 & \(-\)11.0 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Decrease in shaft resistance of the uplift pile.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Depth (mm)** & \(\tau_{s0}\) **(kPa)** & \(\tau_{s1d}\) **(kPa)** & \(-\tau_{s1d}/\tau_{s1d}\) \\ \hline
300 & 2.61 & 4.23 & 0.62 \\
600 & 6.05 & 7.45 & 0.81 \\
900 & 9.49 & 10.66 & 0.89 \\
1200 & 12.87 & 14.01 & 0.92 \\ \hline Average value & 7.75 & 9.09 & 0.85 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Comparison of the shaft resistance of uplift piles and compressive piles.  
The maximum influence range of the additional stress in the soil caused by pile loading is approximately 6 d from the axis of the pile;
2. The uplift pile shows an unloading effect on the surrounding soil, while the compressive pile shows a loading effect on the surrounding soil. A shorter distance to the loading point corresponds to a more obvious unloading effect of the uplift pile and loading effect of the compressive pile;
3. The uplift bearing capacity of the pile is less than the compressive bearing capacity due to the difference between the unloading effect of the uplift pile and the loading effect of the compressive pile, the shaft resistance of the uplift pile is about 0.85 times that of the compression pile;
4. The uplift capacity calculated using the loading and unloading effects proposed in this paper is close to the measured uplift bearing capacity, the method can be applied to calculate the bearing capacity of uplift piles.  
Conceptualization, H.M.; methodology, H.M.; software, Y.M.; validation, H.M.; formal analysis, H.M.; investigation, H.M.; resources, H.M.; data curation, H.M.; writing--original draft preparation, H.M.; writing--review and editing, H.M. and H.Z.; visualization, L.Z. and H.Z.; supervision, H.M.; project administration, H.M.; funding acquisition, H.M. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number 51878618.  
Not applicable.  
Data Availability Statement: Data are contained within the article.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.