Development of a Neutral Plane in PHC-Supported Embankments over Soft Soils: A Case Study of a Motor-Racing Circuit

Piled embankments are becoming widely used to cope with engineering problems (e.g., excessive settlements, bearing failure) caused by soft soil subgrade to maintain the safety and stability of the constructed facilities. This study focused on an international motor-racing circuit currently under construction, where the underlying soft soil substratum characterized by a high void ratio and compressibility may largely influence the long-term performance of the project. Pretensioned high-strength concrete (PHC) pile-supported embankment is designed to improve this project, and its effectiveness remains to be studied. In addition, this study specifically focused on negative skin friction (NSF) and neutral plane (NP) position development, which significantly influence the bearing capacity of the pile foundation and have not been fully understood. As such, two large-scale field tests were performed on the PHC pile-supported embankments to monitor the settlement of piles and the surrounding soils. According to the monitored layered settlements, the NP development with time was quantitatively analyzed, and NP gradually moved up toward the pile top during soil consolidation. Comparison between the measurements of two test sites with and without geogrid reinforcement indicated that geogrids could not only alleviate total and differential settlements of the foundation but also contribute to the shallower final NP position. A numerical model, whose effectiveness was validated by comparing with the field measurements, was established to predict the complete variation of NP positions and explore the effects of various influencing factors through a parametric study. This study enhances the comprehension of NSF and NP development in pile foundations and provides valuable guidance for this motor-racing circuit and other related projects in the future.