Investigations on deep vibratory compaction in sandy soils for desgin optimization and execution quality with respect to effectivity, simulation and control of the achieved soil densification

• Applicants: Professor Dr.-Ing. Frank Rackwitz; Professor Dr.-Ing. Theodoros Triantafyllidis
• Subject Area: Geotechnics, Hydraulic Engineering
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 341427400

The scientific target of the envisaged project is the simulation of soil improvement by the deep vibro compaction method, whereby the design of this type of compaction requires the grid spacing of the densification points on the ground surface based on the density to be achieved, on the power and the diameter of the deep vibrator and on the granulometric soil properties. All these parameters have a significant influence on the densification results. The scientific methods and results of the research unit FOR 1136 will be used within this project although the main efforts within the FOR 1136 were concentrated on the vibro-installation of piles as a geotechnical construction process, which has been treated extensively.Within this envisaged transfer project for the engineering practice, the high cyclic accumulation model (HCA) will be used for the calculation of the deformation accumulation (volumetric as well as deviatoric) of the loose granular soil around the deep vibrator, wherein the extension of this HCA model for large strain amplitudes (in the range of a few percent of strain amplitude) has priority. It is well known that the existing HCA model can only be adapted for strain amplitudes in the per mille range. The numerical simulation of vibro compaction will be conducted on the one hand with the HCA model in a finite element formulation to determine the deformations within a large compactable area around the deep vibrator, whereby the hypoplastic model for the estimation of the deformation amplitudes as input to the HCA model for the entire field will be used. For the simulation of the multiphase medium (soil skeleton, water) the Multi-Material Arbitrary Lagrangian-Eulerian (MMALE) formulation is used to describe the interaction of the vibrator with the immediate fluidized soil close to the vibrator as well as the transition area in the soil between fluidized and compacted zone.Within the proposed project physical model testing of vibro compaction will be performed as a first step of validation of the simulation model. As a further validation step field experiments with the partner responsible for the application will be performed. These field tests will be conducted on selected construction sites of the industrial partner in order to verify the accuracy of the simulation and to validate an additional simplified model, which is aimed to be developed within this project. Finally, this simplified model should serve as an engineering model. It should be able to indicate the required distance between the densification points as well as the accessible final density after the deep compaction as a function of granulometry of the soil and the pre-existing bulk density as well as the power of the used deep vibrator.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: Keller Holding GmbH