Internal Flow Effects on Isotropic Confined Sand-Clay Mixtures

Abstract

International audienceUnder the effect of internal flows, a liner can undergo a washing out of particles, which modifies the particle size distribution and affects hydraulic, chemical and mechanical characteristics. This paper discusses the effects of internal flows on sand/kaolin mixture, in terms of rate of erosion and modification of the hydraulic conductivity. A parametric study is conducted with a specific device that consists of three modified triaxial cells. These cells allow isotropically consolidating and confining specimens, they prevent a parasitic flow and survey large deformations of specimen. The tests reveal that suffusion of clay is accompanied by a clogging in the specimen that induces a drop in hydraulic conductivity. For high gradients the erosion of clay is accompanied by the backward erosion of sand and finally the specimen collapses. The erosion rate then depends on the values of the different parameters considered (hydraulic gradient, clay content and filter pore opening size)

Influence of angularity of coarse fraction grains on internal erosion process

“…Thus the angularity also has an effect on hydraulic conductivity decrease. In conformity with previous conclusions [Reddi, 2000;Bendahmane, 2008;Marot, 2009Marot, , 2011 this decrease in hydraulic conductivity is attributed to particle filtration which may induce a clogging process.…”

“…This pore opening allows the migration of all particles of sand and clay. A smaller pore opening grid would prevent the migration of sand grains, which in turn, would limit the initiation of suffusion process [Marot, 2009].…”

“…The first process consists in a regressive pulling up of the particles from the downstream of the soil to an external middle with an upward development [Lafleur, 1999;Bendahmane, 2008;Marot, 2009]. The suffusion phenomena concerns only the fine particles and results in a diffuse redistribution of particles within the soil.…”

“…The suffusion phenomena concerns only the fine particles and results in a diffuse redistribution of particles within the soil. The global grain size distribution of the soil changes slightly but the hydraulic conductivity can evolve notably [Lafleur, 1999;Bendahmane, 2008;Marot, 2009].…”

A description of internal erosion by suffusion and induced settlements on cohesionless granular matter

“…This can induce a clogging process within the soil and may finally result in a decrease in the hydraulic conductivity [2,14,21]. Therefore, variations of both seepage velocity and pressure gradient have to be taken into account to evaluate the hydraulic loading.…”