Microscopic investigation of the influence of complex stress states on internal erosion and its impacts on critical hydraulic gradients

Abstract

Internal erosion involves the loss of fine particles within the matrix of coarse particles under seepage flow, posing a severe threat to hydraulic structures. This paper focuses on internal erosion considering anisotropic stress conditions. The influence of the anisotropic stress state, represented by vertical stress equal to, bigger than, or smaller than horizontal stress, was investigated using coupled computational fluid dynamics (CFD) and the discrete element method (DEM). Results show that the loss of fine particle specimens under anisotropic stress conditions is greater than that for samples under isotropic stress states, as the loss of fine particles leads to an evolution of anisotropy into isotropy, with local contact force chains gradually forming spatially isotropic structures. The strong force chains of specimens under triaxial compression were also found to develop a dominant orientation in the vertical direction, leading to clogging in the upward migration of fine particles and increasing the critical hydraulic gradient. In addition, the evolution of void ratio, hydraulic drag force, connectivity, and coordination number has also been analyzed to exhibit the influence of stress anisotropy on internal erosion.

A resolved CFD–DEM investigation into the onset of suffusion: effect of confining pressure and stress anisotropy

“…Such reduction is significant, for example, the critical hydraulic gradient of the σ' c = 100 kPa reduces to merely 60% of the original value after the initial stress ratio increases from η = 0 to 0.63. Similar observation between i cr and stress state is also reported in other numerical and experimental studies on gap-graded soils, for example, Wautier et al 60 and Zhou and Yin, 61 Bendahmane et al, 62 Liu et al, 63 and Tomlinson and Vaid. 64…”

“…Similar observation between i cr and stress state is also reported in other numerical and experimental studies on gap‐graded soils, for example, Wautier et al 60 . and Zhou and Yin, 61 Bendahmane et al., 62 Liu et al., 63 and Tomlinson and Vaid 64 …”

“…Given that suffusion usually triggers at relatively small gradient for severely gap‐graded soils ( i cr < 1), only a short suffusion period ( t = 1 s) is performed to keep the total computation time manageable (Figure 7B). Similar rates of hydraulic gradient increase have been adopted in abundant numerical studies 25,53–55 …”

“…Similar rates of hydraulic gradient increase have been adopted in abundant numerical studies. 25,[53][54][55] The above procedure allows for detailed inspections of the flow fields inside the particle assembly and the detached particle movements under seepage. For example, zoomed snapshots of the flow fluid inside the isotropic σ' c = 100 kPa specimen (R100A100) at the onset of suffusion (t = 0.6 s) are illustrated in Figure 8.…”

Numerical simulation of fluid‐particle interaction in geomechanics using an extended CFD‐DEM approach with a super‐quadric model of non‐spherical particles

“…To simulate fluid‐particle interactions, a coupling numerical scheme (CFD‐DEM) for a two‐way coupling between the computational fluid dynamics (CFD) and discrete element method (DEM) was proposed by Tsuji 22 . It becomes an increasingly popular Eulerian‐Lagrangian method for modeling geotechnical problems involving particle‐fluid interactions 23–26 …”