Recent advances in the geotechnics of organic soils and peat - Geotechnics of Organic Soils and Peat - page 172

Figure 7.1 Schematic diagram of charge distribution at the colloid surface ( after Mitchell and Soga,
2005).
ions, because of their single charge, are weakly held, and in solution each has a large
shell of water molecules. On the other hand, calcium ions have double charges and
they are more strongly held, and thus the diffuse layer of calcium-saturated clay is
more compact than sodium-saturated clay.
The presence of the diffuse double layer causes several electrokinetic phenomena
in soil, which may result from either the movement of different phases in respect of
each other including transport of charge, or the movement of different phases relative
to each other due to the electric field (Acar and Alshawabkeh, 1993).
The electrokinetic phenomena include electroosmosis, streaming potential, elec-
trophoresis and sedimentation potential. Electroosmosis is defined as fluid movement
as a result of an applied electric potential gradient (Figure 7.2(a)). Streaming poten-
tial is the reverse of electroosmosis (Figure 7.2(b)). Electrophoresis is the movement
of solids suspended in a liquid due to the application of an electric potential gradi-
ent (Figure 7.2(c)). Sedimentation potential is an electric potential generated by the
movement of particles suspended in a liquid (Figure 7.2(d)).
Electroosmosis and electromigration play a key role in soil stabilization (Acar and
Alshawabkeh, 1993; Barker et al. , 2004).