Erosion Velocity of Large Grains Subjected to a High Uniform Flow Velocity

There is limited knowledge on the erosion rates of large grains. The available erosion models of granular material at large flow velocities are only validated up to a median particle diameter ($d_{50}$) of 1.5 mm. To validate these models with larger grains, erosion tests have been performed on split (crushed rock) with a $d_{50}$ of 8.5 and 21.5 mm. The test results are compared with the erosion models of Fernandez Luque and van Rijn with a combined data set. Results showed that for both theories the measured erosion velocities can be well predicted. It can be concluded that the empirical parameter in the pickup function of Fernandez Luque (${\alpha }_{FL}$) increases with particle diameter. For particle diameters larger than approximately 6 mm, ${\alpha }_{FL}$ becomes more or less constant. The pickup function of van Rijn is applicable over the total range of tested particle diameters. Unfortunately for particle diameters larger than 21.5 mm, it is still not clear which theory is most reliable to estimate the erosion velocities. For the time being, it is recommended to use both functions, with the function of Fernandez Luque as a conservative lower limit.