Buoyancy and local friction effects on rockfill settlements: A discrete modelling

Measured displacements in the upstream shell of rockfill dams show some settlements which can reach a few meters with water levels changes, especially during the first impounding, whereas downstream displacements are smaller. Complementary phenomena are responsible for rockfill collapse due to wetting. Here we numerically investigate the effects of buoyancy forces and the decrease in the coefficient of friction with water on a rockfill column maintained by vertical rigid walls and progressively filled with water. Numerical simulations of the settlements of the rockfill column, using the Contact Dynamics method, are presented. Buoyancy forces seem to have only a negligible influence on the granular pile. Decrease in the friction angle of the rock with water induces rearrangements of the medium, all the more as the decrease is significant. These dynamic rearrangements exhibit an irregular temporal evolution of the granular medium which can be characterized by a phenomenon of local “crisis”. Analysis of the settlements shows that these two combined effects are not the major cause of the settlements observed in rockfill dams and that they cannot in particular explain the settlements.