Effects of Hydraulic Loading History on Suffusion Susceptibility of Cohesionless Soils

Abstract

Suffusion is a selective erosion of fine particles under the effect of seepage flow within the matrix of coarser particles. This complex phenomenon appears as a combination of three processes: detachment, transport and possible filtration of finer fraction. It can induce a change in particle size distribution, porosity and hydraulic conductivity of the material. With the objective to characterize the suffusion susceptibility, downward seepage flow tests were conducted. Four different cohesionless soils were tested under hydraulic gradient controlled conditions or under flow rate controlled conditions. This study shows the significant effect of hydraulic loading history on the value of critical hydraulic gradient.Moreover, method characterizing the erosion susceptibility based on rate of erosion does not lead to a unique characterization of suffusion process for different types of hydraulic loading. The new analysis is based on energy expended by the seepage flow and the cumulative eroded dry mass. The results demonstrate that this approach is more effective to characterize suffusion susceptibility for cohesionless soils.

Modelling of internal erosion based on mixture theory: General framework and a case study of soil suffusion

“…Inspired by the energy approach of Marot and coworkers and also by the thermodynamic implication (Equation ), we suggest the following local suffusion law: where is the coefficient of erodibility of the material, which is an intrinsic property, k F is the hydraulic conductivity, and g is the vertical component of the gravity vector. The right‐hand side term of Equation is in fact the product between k α and the volumetric power dissipated by the flow P seepage . The erosion resistance index I α was found to be independent of the hydraulic loading and of the sample's size upon several laboratory scale studies …”

“…The tests were performed under oedometeric conditions while macroscopic hydraulic gradients were applied. Different water pressures were imposed at the inlet and outlet sections of the specimens, and cumulated (eroded masses) were measured during the tests , . Under these conditions, the tests can be considered one‐dimensional and all the field variables (pressure, displacement, concentration) are only dependent on axial coordinate z and time t .…”

“…Recall that the porosity increment and the cumulated eroded mass increase until E seepage ≤ E max . Beyond this threshold value, we assume that the rate of eroded mass becomes instantaneously zero which is a crude but realistic description of experimental observations …”

“…In addition, the results are provided for four different materials, two different specimen sizes and various hydraulic loading paths to demonstrate the applicability of the new proposed law. This positive achievement is mainly due to the intrinsic character of the material parameter I α that is independent of the specimen size and of the hydraulic loading path …”

Phreatic seepage flow through an earth dam with an impeding strip

“…b) Can new analytical and numerical models of "globalscale" seepage through earth dams add better insights to what the classics [37,38] posed as potential threats to dam stability? c) How to connect these large (dam) scale seepage models to what is tested in column experiments with "core samples" of the embankment porous materials, subject to high and variable gradients (see, for example, [39])? d) Can relatively fast external hydrological/hydraulic drivers, such as a rapid rise of the reservoir level or intensive rain, induce singular (ruinous) consequences via relatively slow seepage flows within the components of a porous dam?…”