Aspects of seismic soil-pile-structure interaction in soft clay by centrifuge testing

This paper presents experimental data from two series of centrifuge tests on pile foundations embedded in a kaolin clay under earthquake excitation. A single pile and two pile-group configurations were tested in the centrifuge at 50g. In the first test series (flight 1) the seismic response of the soil-pile system was monitored, allowing experimentally-driven insights on the kinematic interaction between soil and pile. In the second series of tests (flight 2), a superstructure mass was attached to each foundation model, allowing investigation of the seismic behaviour of the coupled soil-foundation-structure (SFS) system. Two earthquake excitations were analysed during each flight having similar frequency and amplitude characteristics. Results are presented in terms of soil response along a vertical array, pile-caps spectral acceleration and superstructure top-to-ground surface response ratio. Experimental data suggests that for soft soils such as those employed in this experimental campaign, piles may amplify the motion with respect to the one at ground surface, while the natural period of the SFS system may be largely increased compared to its fixed-base counterpart, indicating a strong effect of soil compliance.