Downward drag on the pile surface – Negative skin friction.
Piles installed in freshly placed fills of soft compressible deposits are subjected to a downward drag, a consequence of the consolidation of the strata after the piles are installed. This downward drag on the pile surface. when the soil moves down relative to the pile, adds to the structural loads and is called negative skin friction. This is in contrast to the usual shaft friction which is mobilized when the pile down relative to the soil. Thus, negative skin friction has an effect of reducing the allowable load on the pile.