# Influence of Degree of Saturation on Soil-Pile Interactions for Piles in Expansive Soils
## 5 Conclusions and Recommendations  
This study investigated the influence of the degree of saturation on the pile uplift force and the \(\alpha\) and \(\beta\) parameters for pile foundations in expansive soils. Laboratory tests and theoretical back-calculation methods were conducted to evaluate the relationships among \(\alpha\), matric suction, and swelling pressure. The key findings are summarized as follows:  
* The uplift force developed along the pile shaft during the wetting process exhibited a hyperbolic trend. A significant portion of the uplift force is developed during the early stage of the heaving process. This trend is consistent with the pile heave pattern observed at the TRACON site, and aligns with our observation that the majority of the heave, and thus the associated distress to houses, occurred at the beginning of the construction period.
* The uplift coefficient, \(\alpha\), is a key parameter for computing pile uplift force in pile design for expansive soils. The \(\alpha\) value increases as the initial degree of saturation increases, with a change of approximately 9% within the tested saturation range. Based on the experimental investigation, the back-calculated \(\alpha\) values were relatively constant across soils with varying initial degrees of saturation, suggesting that a constant \(\alpha\) value may be used in design.  
Figure 12: Variation in \(\beta\) value with increasing initial degree of saturation.  
* The \(\alpha\) values obtained in this study fall within a typically accepted lower to moderate range but are notably lower than some of the higher values reported in the literature. This indicates potential variability depending on site-specific conditions, and therefore, it is recommended that the uplift coefficient be validated through field-scale investigations.
* The swelling pressure ratio, \(\beta\), was evaluated to understand the difference between horizontal and vertical swelling pressures. The results indicate that \(\beta\) increases with the initial degree of saturation, with an approximate change of 8% within the tested range. This trend is attributed to a greater reduction in vertical swelling pressure compared to lateral swelling pressure as saturation increases, leading to an overall increase in the \(\beta\) value.
* For practical design applications, the use of constant \(\alpha\) and \(\beta\) values is considered acceptable within the tested range. However, further research is recommended to explore the influence of pile geometry and soil properties in more detail. Previous studies have examined individual factors such as pile length, diameter, soil type, and group pile orientation. Future investigations could benefit from considering these parameters collectively to better understand their combined impact on the behavior of expansive soils. Additionally, it is suggested that the proposed theoretical equation be validated through comparison with field data and other empirical approaches to ensure its accuracy and reliability in real-world engineering practice.  
Conceptualization, K.C.C., A-N.C. and T.H.A.; methodology, K.C.C., A-N.C. and T.H.A.; validation, K.C.C. and T.H.A.; formal analysis, A-N.C. and T.H.A.; investigation, K.C.C. and A-N.C.; resources, K.C.C., A-N.C. and T.H.A.; data curation, A-N.C. and T.H.A.; writing--original draft preparation, A-N.C. and T.H.A.; writing--review and editing, K.C.C.; visualization, T.H.A.; supervision, K.C.C.; project administration, K.C.C.; funding acquisition, K.C.C. All authors have read and agreed to the published version of the manuscript. This research received no external funding.  
Not applicable.  
The data used to substantiate the findings of this study are contained within the article.  
The authors declare no conflicts of interest.