A dam-break on mobile bed constitutes a relevant example of unsteady process with a strong interaction between hydrodynamics and solid transport. For this reason, apart from the classical interest in preventing such dangerous events, the study of the propagation of dam-break waves has become in the last decades a standard benchmark for validating solid transport and hydrodynamic models. In the paper dam-break scenarios over fixed and movable beds, in the presence of a stepped bottom, are considered. In particular, selected literature data and some experimental tests performed in the Water Engineering Lab at University of Cassino (Italy) are compared against numerical results of a two-phase flow model, developed for sediment transport and bed evolution in unsteady conditions. The model is numerically solved using a Finite-Volume method with the first-order multi-stage centered-scheme GMUSTA. The comparisons prove a good agreement between the numerical prevision and the experimental data.