Down-Drag on Pile Groups due to Surface Loading

Pile down-drag due to negative skin friction occurs as a result of downward movement of the soil relative to the pile. Relatively large ground settlements may arise due to the consolidation of the soil as a result of surface loading, lowering of the ground water table or the dissipation of excess pore water pressure generated during pile installation. This paper presents the results of down-drag loading experiments carried out in a geotechnical centrifuge on end bearing single piles, and on 4-pile, 9-pile and 16-pile groups. Extensively strain gauged closed ended aluminium piles with pile stiffness equivalent to that of high quality concrete piles were used. The pile groups were installed 'in flight' by jacking into slightly over-consolidated kaolin clay. The down-drag resulted from the construction of an embankment around the piles. The surface settlement of the clay due to embankment construction is also discussed.