Abstract
Suffusion is one mechanism of internal erosion, which occurs in gap-graded or broadly graded soils when the fine particles are detached and transported by the seepage flow through the void space formed by the granular soil skeleton. Suffusion is therefore a particle scale mechanism. During this microscale, the initial soil fabric may change due to both fines migration and coarse grains rearrangement, leading to an increase/decrease of global/local porosity and hydraulic conductivity, besides of a probable appearance of heterogeneity, which can, in turn, impact the mechanical behaviour of the eroded soil. In the literature, suffusion test results give only a macroscopic point of view and fail to quantify the effect of suffusion at the scale of the soil's induced heterogeneities. In this paper, x-ray tomography is used to get microscopic observations of soil sample microstructure evolution during a suffusion test. The results reveal that suffusion is not a homogeneous process; the removal of fine particles takes place mainly around the soil sample circumference leading to a higher void ratio at the periphery. Besides, the inter-granular void ratio decreases significantly but almost uniformly throughout the sample owing to the progressive collapse and reorganization of the coarse grains induced by the loss in fines.
Highlights
Suffusion is defined as the migration of fine soil particles within the surrounding soil skeleton under seepage flow
Suffusion can lead to an increase in global hydraulic conductivity and seepage velocities as well as settlement in some cases [1], resulting in a change of the soil microstructure, affecting the mechanical behaviour of soil
In addition to the present work, only few and very recent visualisations and analyses of suffusion at grain scale can be mentioned in the literature, either by Hunter & Bowman based on optical techniques [3], or by Mehdizadeh & Disfani based on X-ray tomography [2]
Summary
Suffusion is defined as the migration of fine soil particles within the surrounding soil skeleton under seepage flow. Suffusion can lead to an increase in global hydraulic conductivity and seepage velocities as well as settlement in some cases [1], resulting in a change of the soil microstructure, affecting the mechanical behaviour of soil. The suffusion results in literature give generally a macroscopic point of view and the evolution of soil microstructure (the scale of the soil’s induced heterogeneities) usually is not explicitly mentioned in the existing analysis. In addition to the present work, only few and very recent visualisations and analyses of suffusion at grain scale can be mentioned in the literature, either by Hunter & Bowman based on optical techniques [3], or by Mehdizadeh & Disfani based on X-ray tomography [2]. The changes of the void ratio, inter-granular void ratio and fines content were followed during each suffusion step corresponding to different flow rates
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