  We study the mobility of objects embedded in an immersed granular packing and
subjected to cyclic loadings. In this aim, we conducted experiments using glass
beads immersed in water and a horizontal plate subjected to a cyclic uplift
force. Tests performed at different cyclic force frequencies and amplitudes
evidence the development of three mobility regimes whereby the plate stays
virtually immobile, moves up steadily or slowly creeps upwards. Results show
that steady plate uplift can occur at lower force magnitudes when the frequency
is increased. We propose an interpretation of this frequency-weakening
behaviour based on force relaxation experiments and on the analysis of the
mobility response of theoretical visco-elasto-plastic mechanical analogue.
These results and analysis point out inherent differences in mobility response
between steady and cyclic loadings in immersed granular materials.
