Granular ratcheting phenomena behind a model retaining wall

The ratcheting in a granular soil is an accumulation of irreversible strain under cyclic loading. This effect was experimentally investigated with reference to a small physical model of a retaining wall subjected to cyclic horizontal movements through different granular materials and displacement amplitudes. The model was monitored with a camera in order to derive the displacement field by means of digital image techniques. The main results regarded the variation of horizontal forces at each cycle, the volumetric densification, the surface settlements. The same tests were reproduced at 1:1 scale with DEM investigating the effect of some variables: grain-size, displacement amplitude, initial porosity, oscillation period. As in experiments, a triangular convective cell developed close to the wall, which was originated by the different values of passive and active slope angles. The passive horizontal thrust resulted higher for sand and lower for the smallest glass balls; they increased during cycles up to a steady-state value, which seems to be related to the emergence of some crystalline clusters and a preferential distribution of contact orientations. Stiffer passive thrust-displacement evolutions were also noticed cycle by cycle for displacement values approaching the maximum displacement amplitudes.