Recent advances in the geotechnics of organic soils and peat - Geotechnics of Organic Soils and Peat - page 173

Figure 7.2 Electrokinetic phenomena in soil ( after Mitchell and Soga, 2005).
7.2.1 Electroosmotics
Electroosmosis is the movement of a fluid with respect to a solid wall as a result of
an applied electric potential gradient (Cashman and Preene, 2002). In other words,
electroosmosis involves water transport through a continuous soil particle network,
where the movement is primarily generated in the diffuse double layer or moisture film,
where the cations dominate. When the direct electrical gradient is applied to a clay-
water system, the surface or particle is fixed, but the mobile diffused layer moves and
the solution is carried with it. According to Hausmann (1990), a greater soil particle
surface results in higher moisture film transfers. The electrical potential applied and
viscosity can also affect this phenomenon (Hausmann, 1990). The main mechanism
in electroosmosis is the migration of ions, meaning that the cations migrate to the
cathode and the anions move towards the anode (Tajudin et al ., 2008) (Figure 7.3).
Reuss (1809) discovered that water flow could be persuaded through a capillary by
an external electrical gradient (Das, 2008). There are several theories that describe elec-
troosmosis, including Helmholtz-Smoluchowski theory, Schmid theory, the Spiegler
friction model, Buckingham π theory and ion hydration theory (Gray and Mitchell,
1967).
Helmholtz-Smoluchowski theory is widely used to describe electrokinetic pro-
cesses (Helmholtz, 1879; Smoluchowski, 1921). The theory assumes that the pore