State-of-the-Art Review of Axial Pull-out Capacity of Inclined Piles:  Challenges and Opportunities Ahead

Inclined piles have emerged as a vital foundation element in geotechnical engineering, particularly for supporting structures subjected to significant tensile forces. These piles are engineered to resist axial pull-out loads generated by buoyancy systems, overturning moments from superstructures, and lateral forces from wind, waves, or seismic activity. This review provides a detailed synthesis of the existing literature on the axial pull-out capacity of inclined piles in sand, emphasizing the interplay of critical factors such as pile geometry, inclination angle, embedment ratio, relative density, and soil-pile interface characteristics. This paper presents a comprehensive review of experimental, analytical, and numerical studies on the axial pull-out capacity of inclined piles, with particular emphasis on the inconsistencies and challenges associated with accurate prediction under varied field conditions. It critically examines the limitations of existing analytical models, highlighting the frequent omission of key factors such as soil anisotropy, plug effects, and arching mechanisms. The review identifies significant gaps in current understanding and proposes directions for future research aimed at achieving a more complete characterization of inclined pile behaviour. Recommendations are also provided to guide future investigations and enhance the practical application of inclined piles in addressing contemporary geotechnical engineering challenges.