Comportement des pieux et des groupes de pieux sous chargement latéral cyclique

摘要

Due to wave actions, wind actions, machine vibrations, etc... deep foundations may be subject to cyclic, repeated or periodic transverse and axial loading. These sequences of loadings and unloadings lead to an evolution of the pile behavior and must be taken into account during the design phase. The work presented in this research project focuses on the study of the behavior of centrifuge single piles and groups of 2 x 2 piles under lateral cyclic loading in dry sand. It focuses in particular on the accumulation of displacements at the pile head, the rise of the maximum bending moment due to cyclic loading and the degradation of p-y curves after cyclic loading. In the case of pile groups, the influence of cycles on the group effect, generally characterized by a shadow effect on the back rows of the group, was studied. The effect of the density of the sand and the spacing between piles of the group was also considered. Cycles generate an accumulation of displacements, for the single pile and pile groups, which increase with the level of cyclic loading. A logarithmic formulation in two phases of the accumulation of displacement is proposed for both cases.P-y curves for cyclic loading have been determined and a relationship has been established between the monotonic and cyclic p-y curves for a single pile. For pile groups, in the case of a three-diameter spacing, different relationships are proposed which reflect the location of the pile (pile in the front row or pile in the back row) and the cyclic loading. For axial loading, an instrumented pile for centrifuge testing has been developed. The first results obtained with this pile show very interesting results with a good evaluation of the distribution of load along the pile (shaft friction and tip resistance) during and after the cyclic loading.