An investigation of the effect of soil state on the capacity of driven piles in sands

A series of model pile tests was carried out in the centrifuge, pushing the pile into two sands of very different geological origins and particle strengths. This was accompanied by series of triaxial tests allowing the critical state line of each sand to be established so that the initial in situ state of each sample, prior to pile installation, could be quantified. The work demonstrated that the initial state, defined as the combination of density and stress level relative to the critical state line, is a controlling factor in determining pile capacity, and hence that design approaches based solely on relative density could not be expected to be widely applicable. It was also found that state had to be defined as a ratio of stresses rather than the more usual state parameter in terms of volume. Attempts to verify the method using existing field pile test data were hampered by a dearth of laboratory data accompanying the in situ tests.