Erodibility characterisation for suffusion process in cohesive soil by two types of hydraulic loading

Abstract

An experimental program was set up to study the suffusion process by using a triaxial erodimeter developed in our laboratory. This device is equipped with a multichannel optical sensor in order to characterize precisely the initiation and development of suffusion process. With the objective to characterize the erodibility of clayey sand, tests were performed under either flow-rate-controlled or hydraulic-gradient-controlled conditions. The test analysis allows distinguishing three steps. First, suffusion of a small quantity of clay is detected on downstream. In flow-rate-controlled conditions, this suffusion is immediately followed by a high increase of the hydraulic gradient which continues during the second step. The second step is characterized by very low amount of particles in the effluent. During the third step, high suffusion of clay appears and induces erosion of clay and sand. The results reveal the necessity to take into account the evolutions of hydraulic gradient (or pressure gradient) and also the evolutions of velocity (or flow rate) to represent the hydraulic loading. The analysis based on energy expended by fluid flow and eroded mass permits to characterize the soil sensitivity to clay suffusion and clayey sand erosion for tests under the two types of hydraulic loading.

Suffusion susceptibility investigation by energy-based method and statistical analysis

“…Suffusion susceptibility investigation by energy-based method and statistical analysis. Canadian Geotechnical Journal, 55(1), pp 57-68, https://doi.org/10.1139/cgj-2017-0024 However a fraction of the detached particles can re-settle or be filtered at the bulk of the porous network (Reddi et al 2000;Bendahmane et al 2008;Marot et al 2009;2011a;Nguyen et al 2012;Luo et al 2013). The processes of detachment, transport and filtration of fine particles are thus inseparable.…”

Effects of Hydraulic Loading History on Suffusion Susceptibility of Cohesionless Soils

“…Suffusion tests described in literature, were mostly performed under multi-staged hydraulic gradient conditions in upward direction with hydraulic gradient ranging from 0.02 to 1.4 (Skempton and Brogan, 1994;Ke and Takahashi, 2012;Indraratna et al, 2015) or in downward direction with the hydraulic gradient range from 0.15 to 9.4 (Moffat and Fannin, 2006;Chang and Zhang, 2011). But other tests were also realized under single staged hydraulic gradient with values between 5 and 140 (Bendahmane et al, 2008;Wan and Fell, 2008;Nguyen et al, 2012). Nguyen et al (2012) and Takahashi (2014, 2015) performed suffusion tests under flow rate controlled conditions with a range of discharge per unit cross section from 10 -3 to 0.13 cm.s -1 .…”

A possible characterization of suffusion susceptibility independent of the hydraulic loading history?

“…By carrying out tests on mixtures of sand and gravel with an upward flow, Skempton & Brogan (1994) concluded that the value of the critical gradient of the suffusion initiation, named i cr , is far lower of the value of the critical heave gradient i c (with i c = γ'/γ w , γ': submerged unit weight of the soil specimen and γ w : unit weight of water). The filtration of some detached particles can induce a clogging process within the soil accompanied with the decrease of the hydraulic conductivity (Reddi et al 2000;Bendahmane et al 2008;Marot et al 2009;2011a;Nguyen et al 2012;Luo et al, 2013), which in turn leads to a decrease of the seepage velocity. Therefore, variations of both seepage velocity and pressure gradient have to be taken into account to evaluate the hydraulic loading.…”