Numerical and Physical Modelling of the Effect of a Dam on Powder Avalanche Motion: Comparison with Previous Approaches

As part of the European project CADZIE, the interactionbetween powder avalanches and dams has been studied. First, we simulated a powder avalancheusing a heavy salt solution in a water tank. These experiments showed that (1) the ratio betweenthe maximum velocity parallel to the slope and the front velocity is greater than 1 (up to 1.5),and that (2) the velocity normal to the slope can rise to 74% of the front velocity. The presence ofa dam leads to a reduction of front velocity. The ratio between the maximum horizontal velocityand the front velocity increases with the dam height and reaches a maximum value of 1.9. Aswe did not have access to the density distribution in our experimental set-up, we calibrateda numerical model thanks to the experiments and we deduced the dynamic pressure. Our resultsshowed that, for an avalanche without obstacle, AVAER (Rapin, 1995) and Beghin and Closetʹshypothesis (1990) lead to an overestimation of the dynamic pressure in the lower partof the flow as well as in the upper part, and that the use of front velocity for estimating the lossof kinetic energy leads to an overestimation of the damʹs effectiveness.