Investigation of sand pluviation considering a vacuum - Vacuum Sand Raining (VaSaRain)

• Applicant: Professor Dr.-Ing. Sascha Henke
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 571649836

For the realization of qualitative and significant model and laboratory tests appropriate high-grade test specimens need to be used. Because cohesionless soils, like sands and gravels, loose their internal granular structure during in-situ excavation, the samples are generally reconstructed in the laboratory, thus, restored with the removed sample material. For this, the sand pluviation process has proven to be especially suitable, due to its ability to model the natural deposition behaviour and therefore the granular structure of sediments and to attain different bulk densities. However, this procedure experiences issues if it is conducted with a finer material, like silt or fine sands. Even sand which only contains a small amount of fine content is partially not suitable for the sand pluviation process. The reasons given in literature are the air resistance as well as the air movements during sand pluviation. Smaller particles have, in comparison to their size, a higher air resistance. Thus, these particles in comparison to larger sand grains are stronger decelerated and diverted which leads to smaller bulk densities and a separation of the sample. To prevent this, the sand raining procedure can be conducted in a (partial) vacuum. Thereby the air resistance of especially smaller particles would be reduced, which could prevent the separation of the sample and increase the bulk density. To investigate the effects of the vacuum and the strength of the impact in more detail, within the project vacuum sand raining (VaSaRain) physical as well as numerical investigations will be conducted. For the physical tests an appropriate experimental rig was already constructed during the preliminary work, which allows for the conduction of sand pluviation considering different level of vacuum. With this experimental rig the effects of vacuum on the sample using different set-ups especially different sands with and without fines content, will be investigated. In the process, both the achieved bulk density as well as the density and grain size distribution in the sample will be investigated. This test will be complemented with numerical investigations, which will observe the particle interactions and the air movements in more detail. For this, a coupling between the computational fluid dynamic simulation method (CFD) and the discrete element method (DEM) will be implemented. The findings gained from these simulations will allow to complement the physical tests and to closer understand the underlying effects of the influence of vacuum.

• DFG Programme: Research Grants