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Geomechanics6 - Behaviour of Clay

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Adrian McCallum

on 31 August 2016

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Transcript of Geomechanics6 - Behaviour of Clay

Implications of all this?
Behaviour of clay
Behaviour
of clay
What's clay composed of ?
What shape are clay particles?
The effect of positive cations on the bonding (flocculation) of clay particles...
Recap: What sort of soil is it?
or
Implications?
Clays are also known as
cohesive soils.
Different minerals.....
Recall: What's a mineral?
2D not 3D
Main minerals in the earth's crust:

Oxygen (49.2%)
Silicon (25.7%)
Aluminium (7.5%) +
Fe, Ca, Na, K, Mg etc.
So what's clay primarily formed of?
Atomic Structure of Clay
Tetrahedrons
Octahedrons
and
These structural units combine to form sheets:
and then combine in different combinations to form:
Sivakugan & Das (2010)
Same components, just different arrangement & bonding.
Hydrogen bonds
(strong)
Potassium bonds
(not as strong)
van der Waals forces
(weak)
Implications?
Montmorillonite (or smectite)
Weak van der Waals bonds allow water between sheets resulting in swelling, thus:
expansive clays
.
Water within clay results in:
Negatively (- ve) charged clay particles
Would kaolinite be expansive or not? Why?
What are the implications
of this - ve charge?
Make a list.....
Why?
Because they:

have a large surface area (because of their shape), and
are attracted together by electric charges.
Next week...
Think on the implications of such bonding...
Adapted from Sivakugan & Das (2010)
& Sivakugan (2009)

From Sivakugan
From Sivakugan
these two types of sheets:
Silica Tetrahedral Sheet
Alumina Octahedral Sheet
That can be combined in different ways!
Resulting in different behaviour...
Padlet!
Specific Surface Areas
kaolinite:
15
square metres / gram

illite:
80
square metres / gram

montmorillonite:
800
square metres / gram
Because clay is -'vely charged it attracts +'vely charged water molecules
Resulting in...
This means:
Clays can be very reactive.
(Also called expansive soils)
Mineral: "A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes."
Element: a pure substance consisting of one type of atom
Compound: combination of two or more elements
Soil Compaction...
Full transcript