Matyas, E. L. and Santamarina, J. C. (1994). "Negative Skin Friction and the Neutral Plane." Canadian Geotechnical Journal, Vol. 31, No. 4, pp. 591-597
Current views indicate that negative skin friction on piles can be mobilized at small relative deformations and should be considered in all designs, primarily for serviceability conditions. An elastic-plastic closed-form solution is presented that permits an estimate of down-drag forces and the location of the neutral plane. It is shown that the conventional rigid-plastic solution may overestimate down-drag forces by as much as 50% and may also overestimate the depth of the neutral plane.