For granular materials exposed to surface flow, cohesion plays a key role in erosion resistance.
Source: BAM, Buildings and Structures Division
Despite the relevance of surface erosion in a wide range of physical and industrial contexts, some of the key questions concerning erosion of cohesive materials are still an open challenge for both the engineering practice and scientific community. In this sense, it is currently still very difficult to produce reliable erosion predictions addressing the WHEN (the critical conditions for the onset of erosion) or HOW FAST (the evolution of mass loss) for general systems involving granular cohesion.
This paper makes use of a micro-mechanical simulation technique to analyse a form of surface erosion (namely the erosion produced by a fluid jet) on bonded granular samples and proposes a macroscopic interpretation model to evaluate the simulated data. This approach is capable of reproducing and quantifying the main physical mechanisms both at the erosion onset and throughout the scouring process, in fair comparison with previous experimental data.
However, the simulated results also highlight two important aspects, both of which call into question the appropriateness of the classical erodibility theory:
- For a given cohesion strength, the obtained erodibility parameters seem to depend significantly on the entry velocity of the fluid, which undermines their assumption as intrinsic (in this respect, constant) material properties.
- The critical fluid stress conditions observed at the final eroded state deviate significantly from those estimated at the onset, which directly contradicts one of the basic assumptions of the erosion theory.
A critical review is thus performed both on the limitations of the numerical model as well as on the possible causes for the discrepancies. A first attempt to address these questions is discussed here reflecting the strong spatial and temporal fluctuations of the fluid flow at the granular surface.
The paper finally concludes with a perspective on future studies on this subject, outlining simpler (and therefore better controlled) erosion configurations to revisit the classical erosion laws in clearer conditions (concerning both the erosion geometry and the fluid flow).
The ultimate goal and value of this and future contributions is the development of a robust theoretical framework to quantify and hopefully prevent serious erosion risks to society, for instance those leading to catastrophic failures of civil infrastructures (e.g. erosion of earth-dams and flood-protection dikes).
On the erosion of cohesive granular soils by a submerged jet: a numerical approach
Z. Benseghier, L.-H. Luu, Pablo Cuéllar, S. Bonelli, P. Philippe
published in Granular Matter, Volume 25 ,Issue 8, Pages 1–20.
BAM Department Safety of Structures
BAM Division Buildings and Structures