Coupled micromechanical modelling for the analysis and prevention of erosion in hydraulic and offshore infrastructures
Final Report Abstract
This project is concerned with the behaviour and modelling of granular soils with solid cohesion, aiming to address the erosive failure of hydraulic and offshore infrastructures. The approach here involves a multi-scale perspective, with particular focus on the cemented bridges at the grain scale and emerging towards the macroscale geotechnical application. The context of the project lies in the localized erosion and fluidization problems that may trigger the mechanical failure of civil constructions such as flood-protection dikes or the foundations of offshore wind turbines. In fact, the erodibility and mechanical resistance of the soils involved in such systems can be governed by the presence of solid cohesive bridges in between grains. In this sense, the project aims to assess the impact of this cementation on the behaviour of granular soils to clarify the mechanisms at play during a hydrodynamic solicitation until material failure. A micromechanical approach is used to directly examine the interactions between a fluid and the bonded assembly of solid particles without resorting to ad-hoc constitutive assumptions. The challenge here is to retain all the richness of the microscopic description of cemented bridges and of the grain-resolved fluid interaction while addressing geotechnical problems at the engineering scale. Two complementary investigation lines were thus pursued involving physical experiments with controlled artificial materials and grain-resolved numerical simulations combining the Lattice Boltzmann and Discrete Element methods. An important milestone of the project was the experimental characterization of the artificial cohesive geomaterials themselves (glass beads bonded by solid paraffin bridges) carried out by the French partners. They managed to carefully measure the mechanical strength of the cemented materials both at the grain-scale and meso-scale using a variety of test configurations (single bond and sample traction, shearing, bending and torsion). This was then complemented with physical tests on the modes of hydraulic failure of granular cohesive samples subjected to a localised inflow at their base. The numerical work focused on the development and calibration of a 3D granular cohesion model based on a preliminary 2D model. The cohesion model was then tested and validated with three sets of laboratory results at the mesoscale and it has been integrated into the high-performance simulation framework waLBerla. This has finally permitted the coupled 3D simulation of a local fluidization scenario developing within a granular sample and underneath a solid wall under cross-wall pressure difference, reproducing in essence the piping failure of a suction-bucket foundation in small scale. The choice of the waLBerla framework has motivated a fruitful collaboration with the FAU University of Erlangen, leading to a follow-up project in the frame of the EU-funded CEEC network (Centre of Excellence for Exascale CFD), where a large-scale counterpart of the small-scale piping simulation achieved here shall be performed using large supercomputers.
Publications
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Micromechanical framework for a 3D solid cohesion model –implementation, validation and perspectives. 7th edition of the International Conference on Particle-based Methods. CIMNE.
Sanayei, M.; Farhat, A.; Luu, L.; Werner, L.; Rettinger, C.; Philippe, P. & Cuéllar, P.
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Multi-scale cohesion force measurements for cemented granular materials. EPJ Web of Conferences, 249, 08008.
Farhat, Abbas; Luu, Li-Hua; Philippe, Pierre & Cuéllar, Pablo
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Experimental investigation of mechanical and hydro-mechanical behaviour of artificial cemented granular soils. ALERT Workshop 2022, 26th-28th September 2022, Aussois, France
Farhat A., Philippe P., Luu L.-H., Cuéllar P., Benahmed N. & Wichtmann T.
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Hydraulic failure of a weak cemented soil barrier subjected to localized underflow. 28th EWGIE Annual Meeting, 19th-21st July 2022, Sheffield, UK.
Philippe P., Farhat A., Balagani, Luu L.-H. & Doghmane A.
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Fluidization and erosion of cemented granular materials Experimental characterization and micromechanical simulation. PhD Thesis. Aix-Marseille University, Doctoral School “SCIENCES POUR L'INGENIEUR : Mécanique, Physique, Micro et Nanoélectronique, Spécialité Mécanique des Solides”
Farhat, A.
