Etude en chambre d'étalonnage du frottement sol-pieu sous grands nombres de cycles. Application au calcul des fondations profondes dans les sols fins saturés

摘要

This Ph.D. dissertation focuses on the behavior of the pile-soil interface under cyclic loading. In this context, an experimental program was conducted on the Navier calibration chamber using an instrumented pile-probe and a piezocone installed in saturated clay samples. In order to carry out this study, we developed, In particular a slurry consolidomètre prototype to reconstitute fully saturated clay samples. Special attention was given, during displacement controlled cyclic tests, to local friction evolution mobilized at the pile-soil interface and mobilized tip résistance. The experimental study has allowed the demonstration of the influence of the key parameters on the observed behavior and more specifically, on the local friction at the interface. We examined, in particular, the influence of amplitude of cyclic displacement, the frequency of cyclic loading and the applied number of cycles. Emphasis was put on the case of large number of a few hundred thousand of cycles that is still little studied in the literature. We also study the influence of initial consolidation pressure. The experimental results allowed us to identify, after an initial phase of stress softening, a new phase of stress hardening of local friction. This behavior is not yet described in the literature. The stress softening phase is related to the progressive generation of pore water pressure while the stress hardening, for its part, is related to a gradual dissipation of the generated pore water pressure. Furthermore, a complete sequence of monotonic and cyclic tests were conducted on a piezocone in order to quantify, in a precise manner, the generated pore water pressure at the pile-soil interface during different loading phases and thus validate interpretations given for stress-softening and stress-hardening phases based on the observed results.