Scale effects in piles and nails loading tests in sand

The question of scale effects is obviously of first importance in centrifuge testing. The paper deals with the problem of modelling piles and nails in sands. It first describes the large series of centrifuge pull-out and torsion loading tests that have been carried out on vertical model and on plates. Scale effects of different parameters on shear stress development are investigated : pile diameter and roughness, grain size (d50), centrifuge acceleration. A good correlation is found between the normalised roughness and the coefficient of friction. The results show that the model's diameter must be more than 100 times d50 to reduce scale effects on the maximum shear strength and on the displacement needed to mobilise the interface shear stress.