Abstract:
Use of grounds with soft compressible layers at shallow depths for development projects
requires the use of pile foundations to support the structural loads. Piles installed through
soft compressible soil layers are subjected to Negative Skin Friction (NSF) as a result of
consolidation of the soft compressible layers due to placing fills, lowering of the ground
water table, pile driving etc. The NSF, or commonly referred to as the drag force, is
generally estimated from the skin frictional resistance due to the consolidating layer and
layers above it. However, it is shown by the researchers [Bjerrum et al. (1969) and Endo et
al. (1969)] that the NSF is not developed up to the bottom of the consolidating layer but
only upto a point, referred as the neutral point, above the bottom of the consolidating
layer. Moreover, the results of full scale field tests conducted by researchers clearly
indicates that the development ofNSF is not due to the total stress but due to the effective
stress acting on the pile shaft. Moreover, it is experimentally shown that the development
of the ultimate NSF requires very small relative displacement between the pile and the
soil. Furthermore, it is experimentally shown that the action of short-term live loads
reduces the developed NSF. Therefore, the NSF and short-term live loads are not
simultaneously acting on the pile.
