Extending the Shields criterion to erosion of weakly cemented granular soils

Pierre Philippe,Florian Brunier-Coulin,Stéphane Bonelli,Pablo Cuéllar,Li-Hua Luu,Zeyd Benseghier

doi:10.1051/epjconf/202124908009

Abstract

This contribution tackles the issue of incipient conditions for initiation of erosion by a fluid flow at the surface of cohesive materials. To this end, a typical assessment procedure consists of subjecting a soil sample to progressive hydrodynamic stresses induced by a submerged impinging jet flow whose injection velocity is gradually increased. This paper presents the results of an extensive use of this protocol both in experiments and numerical simulations, the latter being based on a coupled DEM and LBM approach. Here we consider the specific case of weakly cemented soils, either made experimentally of glass beads bonded by solid bridges or modelled numerically by a solid bond rheology with a parabolic yield condition involving the micromechanical traction, shearing and bending of the bonds. The results show that, as expected, the hydrodynamic stress for erosion onset substantially increases with solid cohesion as compared to cohesionless cases but can, however, be satisfactorily predicted by a simple extension of the usual Shields criterion that only applies for cohesion-less granular sediments. This extension includes a cohesion number, the granular Bond number, with a simple definition based on tensile yield values.

Highlights

The ability to better understand and correctly predict sediment erosion and transport is of paramount interest owing to the large number of related practical situations in nature or industry
This condition can be quantified by a critical value Sh0∗ of the so-called Shields number Sh0, which is the dimensionless ratio between the shear stress exerted by the fluid flow over the sediment and the buoyant weight of a single particle
Data from several experimental tests and numerical simulations of erosion tests are represented in the two Shields diagrams of Figure 1 and Figure 2

Summary

Introduction

The ability to better understand and correctly predict sediment erosion and transport is of paramount interest owing to the large number of related practical situations in nature or industry. For strictly non-cohesive materials, erosion can be considered as a grain-by-grain process that initiates as soon as the fluid flow stress exceeds both the particle weight and the frictional forces at the sediment’s surface This condition can be quantified by a critical value Sh0∗ of the so-called Shields number Sh0, which is the dimensionless ratio between the shear stress exerted by the fluid flow over the sediment and the buoyant weight of a single particle. The objectives of the present study are multiple: (i) to extent the applicability of the Shields criterion to weakly cemented sediments; (ii) to compare real experimental results with their numerical counterparts from a 2D DEM-LBM modelling; (iii) to evaluate a characteristic cohesive stress and define a granular Bond number at both contact and sample scales To this end, the experiments and the numerical approach with a common protocol are both described in section 2 while section 3 presents the results, including a comparison between experiments and simulations. To conclude we propose an extended and more general formulation for the critical Shields number involving the granular Bond number but still restricted to the present specific cohesion generated by weak cemented bonds within a granular material

Objectives

Methods

Results

Conclusion