Numerical analysis of negative skin friction on piles in soft clay

Negative skin friction is considered one of the problems in the design of piled foundations in soft soil. The negative skin friction induces an additional compressive force on the pile called the dragload as well as, an additional pile movement called the downdrag. Ignoring the effect of negative skin friction in the design of piles leads to structural, and serviceability problems. The dragload depends on various factors such as, pile characteristics (method of installation, material, and surface treatment), soil properties (shear strength and compressibility), pile–soil relative movement, and degree of consolidation. In this paper, an axisymmetric finite element model was used to simulate, and analyze the pile–soil interaction problem of negative skin friction. The soft soil was simulated by the double hardening soil model, and the pile was described by a linear elastic model. A field case study for two instrumented end bearing driven pipe precast concrete piles in Bangkok soft clay was back analyzed. The various approaches to model the pile element, and load configurations were analyzed, and compared. An extensive parametric study was carried out to investigate the effect of different factors on the dragload value, neutral plane location, slip length, and pile movement.