Slender piles

The computer programme PGROUP (Highway Engineering Computer Branch of the Department of the Environment, U. K. ) was used to analyse the global pile cap flexibility matrix of slender piles. It was found that for stiff piles embedded in soft soils, the vertical flexibility of the cap was reduced for increased pile slenderness. Instability due to pile wandering during installation, called flutter, was examined as a limit to the feasible pile slenderness. Instability due to buckling was also examined. Model tests, at very small scale (3.18 mm and 6.35 mm diameter piles) were carried out to verify the validity of PGROUP in predicting the settlement ratio of groups of stiff piles in soft cohesive soil. They also pointed out the inability of PGROUP to model the lateral load response of the piles in such soil. A parametric study of the PGROUP flexibilities, for single piles, 3-pile groups, and square arrangements of 4, 9, and 16 piles, was carried out, producing design curves and charts of use to the pile designer.