The flow direction is generally different from the gravity direction in geotechnical structures or slopes, the effect of which during suffusion remains unclear. This paper presents a coupled computational fluid dynamics and discrete element method approach to simulate the particle–fluid interaction relevant to this problem. The CFD-DEM approach is first benchmarked by a classic granular system problem, which is then used to investigate the characteristics of suffusion and its impact on the mechanical behavior. Five different angles between gravity and seepage directions for gap-graded soils with two fines contents are examined. Both the macroscopic and microscopic characteristics during suffusion and triaxial loading tests are analyzed. The direction angle is found to play a significant role affecting the erosion process and the mechanical consequence of soils. The results show that the greater the angle is, the harder it is for suffusion to occur and continue.

Investigating the effect of flow direction on suffusion and its impacts on gap-graded granular soils

Understanding the effect of particle size on the shear strength of granular materials is important for geotechnical design and construction. However, previous studies show contradicting results on the relationship between particle size and shear strength. Additionally, the effect of particle breakage on this relationship has not been fully revealed. In this study, a series of biaxial tests have been simulated with the discrete element method to explore the particle-size effect of sand considering the role of particle breakage. The sand specimens have parallel particle-size distributions. The sequential breakage model has been used to simulate particle breakage, which is a combination of replacement and cluster methods. The main conclusions of this study are: (1) the relationship of peak shear strength and particle size depends on the crushability of particles and relative density of specimens; (2) the particle size and crushability have a very slight effect on the residual shear strength; and (3) at the microscale, the relationship between shear strength and particle size is positively related to the friction utilization ratio. 

Micromechanical Investigation of Particle-Size Effect of Granular Materials in Biaxial Test with the Role of Particle Breakage

As a typical form of internal erosion, suffusion refers to the detachment and migration of fine particles through voids among coarse particles driven by seepage flow. This paper studies the...

Suffusion-Induced Evolution of Mechanical and Microstructural Properties of Gap-Graded Soils Using CFD-DEM

Effect of particle breakage on the behavior of soil-structure interface under constant normal stiffness condition with DEM

Coupled CFD–DEM Investigation of Erosion Accompanied by Clogging Mechanism under Different Hydraulic Gradients

This paper presents a numerical study of the effect of fine content on the mechanical behavior of bidisperse granular materials using the discrete element method. Triaxial compression tests are performed on different samples with fine contents varied from 0 to 40%. It was found that, starting from 20%, fine content has a visible effect on the shear strength. The optimal fine content is about 30%, at which the shear strength is the best. An investigation into the granular micro-structure showed that the fine particles, on one hand, come into contact with coarse particles, but on the other hand, separate the latter ones as fine content increases beyond 20%. Thus, the part of the shear stress carried by the coarse–fine contacts increases, while the part carried by the coarse–coarse contacts decreases. For fine content ≤ 30%, the coarse–coarse contacts primarily carry the shear stress. Above this optimal fine content, the fine–coarse contacts overtake the coarse–coarse ones. The fine–fine contacts have little contribution to supporting the shear stress. For the studied range of fine content, the coarse particles primarily carry the shear stress, leaving the fine particles under relatively low stresses. Moreover, the matrix composed of fine particles is greatly softened by the shear loading. A classification of binary mixtures depending on their micro-structure was also proposed.

Micro-scale investigation of the role of finer grains in the behavior of bidisperse granular materials

A DEM study of the effect of the loss of fine particles on the mechanical behavior of gap-graded soils

In this paper, we present a micro-mechanical study of the effect of fine content on the behavior of gap graded granular samples by using numerical simulations performed with the Discrete Element Method. Different samples with fine content varied from 0% to 30% are simulated. The role of fine content in reinforcing the granular skeleton and in supporting the external deviatoric stress is then brought into the light.

/pdf/micro-mechanical-investigation-of-the-effect-of-fine-content-3xxljfigs1.pdf

Micro-mechanical investigation of the effect of fine content on mechanical behavior of gap graded granular materials using DEM

The ability of granular materials to retain fine particles transported within their void space by seepage flow depends strongly on the geometric characteristics of their pore network (pore sizes and constriction sizes). Hence, characterizing the pore network of a granular assembly obtained by means of a micro-tomography scanning or a numerical discrete simulation is of great importance in assessment of its filtration efficiency. Here, we determine characteristics of the pore network of virtual samples composed of spherical particles simulated by using the DEM. A new criterion is proposed to merge neighboring tetrahedra issued from the weighted Delaunay triangulation. To do so, we extend the concept of inscribed void sphere, initially defined for each tetrahedron, to each polyhedral sub-domain constituted of merged tetrahedra. This inscribed void sphere fits the best the void space within the sub-domain. Flat tetrahedra are first eliminated by a primary merging procedure taking into account two basic geometric conditions required for each pore. Adjacent sub-domains are then merged depending on the level of overlap between their inscribed void spheres. The pore size distributions and constriction size distributions (CSD) of granular samples with different grain size distributions obtained with the new merging criterion are compared to those given by two other criteria often used in the literature. The new criterion allows us to reduce greatly the inherent subjectivity in characterizing the granular pore network and to remediate the drawbacks of the two considered criteria in the literature. Moreover, CSDs given by these different criteria tend to converge for gap-graded and widely graded materials. The CSDs obtained with the new merging criterion are used to estimate the controlling constriction sizes $$D_c^*$$
 of the considered samples, and the estimated values of $$D_c^*$$
 are compared to Kenney and Lau’s empirical rule.

A new Delaunay triangulation-based approach to characterize the pore network in granular materials

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Papers

Micro-scale investigation of the role of finer grains in the behavior of bidisperse granular materials

A DEM study of the effect of the loss of fine particles on the mechanical behavior of gap-graded soils

Micro-mechanical investigation of the effect of fine content on mechanical behavior of gap graded granular materials using DEM

A new Delaunay triangulation-based approach to characterize the pore network in granular materials