Evaluation of local soil-pile friction in saturated clays under cyclic loading

Abstract

This paper presents laboratory measurements of mobilized local friction along piles subjected to very large numbers of axial loading cycles. The experimental approach used here is of the physical modelling type and consists of testing an instrumented prototype pile-probe installed and loaded in specimens of saturated clay reconstituted in a calibration chamber. The procedure developed for evaluating the local friction mobilized upon monotonic loading and the further evolution of local friction during the application of displacement-controlled cycles is described. After the installation of the probe, a succession of monotonic and cyclic displacement-controlled loading phases, carried out on a reference kaolinite, is presented and analysed. During the cyclic sequence, carried out up to 105 cycles, an initial phase of friction degradation is observed, followed by a reinforcement phase, which continues until the end of the test. A coefficient of evolution is defined which allows for the quantification, during the application of the cycles, of the evolution of mobilized friction in terms of the degradation or reinforcement of friction. The evolution of the friction mobilized during the application of the cycles is interpreted in terms of the combination of excess pore water pressure generation and dissipation. A comparison is made between the maximum static shear mobilized before and after the cycles, which shows the influence of the cyclic sequence on this quantity. Elements are finally given on the repeatability of the test, showing a fairly good level of repeatability.