3D Numerical Modeling of Negative Skin Friction Effects on Tapered Piles in Soft Soils

The surrounding soil of pile foundations may settle as a result of fill placing or even consolidation, especially in soft grounds. If the soil settlement is higher than the pile's, Negative Skin Friction (NSF) happens. NSF can have a hanging effect on piles which causes pile settlement (downdrag) and applies extra force (dragload) on pile. This study numerically investigated the effects of various tapering angles (alpha) of single piles and pile groups on NSF as well as Neutral Plane Depth (NPD) in fine-grained cohesive soil. Analyses were performed in three-dimensional (3D) form using ABAQUS, a Finite Element Method (FEM) software. The results showed that although tapered piles either in single and group can be economically beneficial, they may experience an increase in NSF by up to 46.7% in single piles and 28.1% in group piles. Similarly, it was observed that NPD values rise with tapering angle. Consequently, the bearing capacity of single tapered piles and tapered pile groups decrease as a result of dragload caused by increased NSF compared to the tapered piles placed in coarse-grained soils discussed in previous studies. Notably, in pile groups, center piles experienced smaller NSF and NPD in comparison with side and corner piles since the soil between the piles experience smaller settlements as a result of group effect.