Thank you for your answer.
Nevertheless, I am still unable to do the conversion between volume and mass. For exemple I have a cumulated mass of 0.4463321 tons and a corresponding cumulted volume of 2.16.10^(-3) m^3. I have chosen a specific gravity of 2.65 and a shape factor of 0.6. The density of sand is 1489kg/m^3. (I only used sand in the simulation). But if I multiply the cumulated volume by a density, I don’t have the cumulated mass I would like to obtain.