Experimental investigation and development of a theoretical model for the vibrofluidisation of dry granular materials

• Applicant: Professor Dr.-Ing. Frank Rackwitz
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 461480840

The aim of the proposed research project is the development of a theoretical model for describing the vibrofluidisation of dry granular materials like sand, based on the results of geotechnical laboratory tests. This theoretical model is then supposed to be transferred into a material model suitable for implementation into a finite element program in order to solve later complex geotechnical boundary value problems.In this context, vibrofluidisation means the emergence of fluid-like properties within a granular material subject to vibrations with large acceleration amplitudes. Fluid-like properties are, for example, a reduced shear strength or complete lack thereof, viscous stress components and hydrostatic stress states or the evolution of convective motions. Although the existence of this phenomenon has long been known in the world of geotechnical engineering, only few studies and incomplete approaches toward it’s explanation exist. Since recent findings suggest the relevance vibrofluidisation has for construction techniques like vibratory pile driving and vibrocompaction, a need for further research can clearly be stated. The research project focusses on the deformation behavior and shear strength reduction of granular materials, while being subjected to vibrations. The latter is attributed to the emergence of a collisional stress caused by oscillating grains, the reduction of effective stresses due to inertial forces and the reduction of mobilized friction due to steady grain movements.The experimental work will consist of oedometric tests for investigating the compactive behavior, as well as triaxial tests for investigating the shear strength during vibration. For this purpose, conventional cells will be mounted on shaking tables and modified, so that the loading can be applied pneumatically. Model tests simulating the settlements of a foundation on sand under vibrations will be performed as a means of validating the material model.Developing this material model will be the subject of the theoretical work, as well as the implementation into a finite element program and the validation with the results of the executed laboratory tests.

• DFG Programme: Research Grants