Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay
Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay
Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay
a)
Still not
neutral; ∴
continues
to form
octahedral
sheets
3 Plagioclase
Order indicates relative
4 Calcite
abundance in sand
5 Dolomite
6 Muscovite
Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay
The other fundamental unit is Octahedron
3-OH -3
1-Al +3
3-OH -3
Aluminum octahedron
3-OH -3
1-Mg +2
3-OH -3
Magnesium octahedron
Formed by typically
70 – 100 elementary
layers
t/l =1/10
t = 100 – 1000 Å
Cluster of plates
(resembles pages
in a book)
Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay
Montmorillonite Pure seams of Montmorillonite
(e.g. Wyoming Bentonite)
Also known as Smectite
and is 2:1 clay mineral
400 Å
Among clay
minerals, Sodium
montimorillonite has
the smallest and
filmy particles
1000 - 5000 Å
10 - 50 Å
a) b) c)
a) Model of water molecule; b) Relative location
of atoms in the water molecule; and c) Polar
representation of water molecule
+vely charged
cation
Polar water
molecule
Adsorbed water
can not be
removed by oven-
drying at 105-110°C
and may therefore
be considered to
be part of the solid
soil grain.
Variation of viscosity
with distance from
particle
Illite 40
Montmorillonite 80
Al3+ > Ca2+ > Mg2+ > NH4+ > K+ > H+ > Na+ > Li+
This indicated that, for e.g. Al3+ ion can replace Ca2+
ions and Ca2+ can replace Na+ ions. The process is
called CATION EXCHANGE.
Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay
Practical example for Cation Exchange
Stabilization of Sodium based Clay soil using Lime
Low ion
concentration in the
Net soil water
repulsion
Distance
between crystal
High ion faces
Net concentration in the
soil water
attraction
Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay
Dispersed Structure of clay soils
-The net forces of repulsion are greatest in the
case of particles approaching face to face.
Lacustrine clays
(deposited in fresh
water lakes) generally
have a dispersed
structure. In this case,
few of the particles
are in direct contact,
most being separated
by the adsorbed
water layers.
Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay
Flocculated Structure of clay soils
-Marine clays (deposited in sea water in which ion
concentration is high, so that the adsorbed water
layers are thin) generally have flocculated
structure.
Void space
Flocculated structure
has open structure
with large void
spaces with particles
attached to each
other with edge to
edge and edge to
face contacts.
Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay
Structure of clay soils (Fine-grained soils)
Typical arrangement of platelet particles
a) Dispersed b) Flocculated
Low ion concentration High ion concentration
(PH < 7)
Silt/sand size
particle
Remolding of
flocculated
structure results
in dispersed
structure
Geiger-MÜller
counting tube
2θ = Angle of
the counter
Demerits:
(i) Not suitable for soils with mixtures of
clay minerals, organic matter and non-
clay mineral constituents and
(ii) Inability to specify proportions of
each mineral in a mixture.