Geoscience Reference
In-Depth Information
Fig. 18.13 Effect of alum
(aluminum sulfate)
concentration on percentage
on soil bentonite dispersion:
a percentage of dispersion
and b density variation in
dispersed-treated bentonite
(Ouhadi and Goodarzi
2006
)
Reprinted from Ouhadi and
Goodarzi (
2006
). Copyright
2006 with permission from
Elsevier
on runoff
reduction
in the PSD-phosphogypsum-treated
soil,
compared
with
untreated or only phosphogypsum-treated soils, is clearly observed.
PSDs are applied to soils mainly in arid and semiarid areas, where rainfall and
irrigation control soil water transmission properties; because this is a continuous
remediation procedure, polysaccharide-induced soil changes are irreversible on a
lifetime scale.
Alum Dispersivity of a soil is determined by the amount and type of soil clay and
by the presence of Na as saturated cation. Dispersive clay soils exhibiting a low
permeability and a low water velocity prevent transport of soil particles. However,
once cracks develop, dispersed soil-clay particles are easily carried with water
flowing through these cracks. In general, soil dispersivity in agricultural lands is
controlled by gypsum product additives. However, for specific geotechnical pro-
jects, alum or aluminum sulfate (Al
2
(SO
4
)
3
18H
2
O) is also used. Ouhadi and
Goodarzi (
2006
) tested the stability of dispersive soil clays following alum treat-
ment (Fig.
18.13
). It can be observed that the adding of 1.5 % alum, for example,
caused the percent dispersion of the soil bentonite to drop to 40 % and then
