Stress-level effects in model tests on piles

Abstract

Results are presented from several series of centrifuge model tests of piles installed in beds of uniform dry sand. Using identical model geometries, but varying acceleration factors, the tests demonstrate quite clearly the nature and extent of stress-level variations on the performance of piles. The results are interpreted initially in terms of bearing capacity coefficients Nt and lateral earth pressure coefficients Ks, and subsequently in terms of angle of friction [Formula: see text], determined using available relationships. Controlled laboratory experiments with varying levels of overburden pressure around the piles indicated consistent reductions in Nt, and to a lesser extent in Ks. Quantitative interpretations in terms of angle of friction variations depend on selection from a range of empirical correlations available and have been made for two of those commonly used. Comparison of shaft loads in compression and extension confirms the widespread belief that there is a difference, which is found to vary quantitatively depending on the relative density. Key words : model tests, piles, sand, centrifuge, stress level.