A model study of negative skin friction on a fixed base pile in soft clay

Abstract

In this research programme, a small-scale laboratory test was carried out to investigate the phenomenon of negative skin friction through studying the interaction between a pile and the surrounding soil and to obtain, by means of an instrumented 50mm diameter model pile, an expression for the magnitude and distribution of negative skin friction for an end-bearing pile in soft clay. The programme included measurements of pore water pressures using miniature piezometers, both vertically along the pile shaft and laterally from it, as the pattern of dissipation of this pressure controls the distribution of negative skin friction along pile length at any given time. Two testing programmes were conducted. Each testing programme consisted of applying load increments on the soil up to 90 kPa as surcharge pressures. Pore pressures, settlements and pile loads were monitored until 90% consolidation had been achieved. From test results, expressions relating the surcharge pressure and soil shear strength with the developed negative skin friction have been established. The study has been extended to include predictions of negative skin friction and pore water pressures by the use of Numerical Methods such as the Finite Element Method and the Finite Difference Method. Results obtained by these methods have been compared with those measured.