Advanced Soil Mechanics CE 6401 Slide Lecture 1

Advanced Soil mechanics slides

1. Lecture Plan
•Soil water, porosity and moisture effects relative
to effective stress principles
•Capillarity, permeability and frost action
•Hydraulicfracturing
•Flowofwaterthroughsoils;seepageanalysisfor
isotropicandanisotropicconditions
•Numericaltechniques for vertical and radial
drainage
•Soil improvement techniques: description,
procedure and usage; preloading, dynamic
consolidation, vibro-compcation, drains, lime
treatment and earth reinforcement, etc.

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Concept of Diffuse Double layer/ adsorbed water

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❑A clay surface probably behaves as an effectively uncharged surface if the
negative charge on the lattice is neutralized by monovalent cations that are
tightly bound to the surface. But if the cations are hydrated a proportion tends to
dissociate from the surface and will cause an electrical potential gradient to be
set up near the surface.
❑The surface of a clay particle, being negatively charged, attracts positive ions.
This region of attracted positive ions in solution and the negatively charged
surface of the clay is termed the ‘diffuse double layer’.
❑The diffuse double layer occurs at the interface between the clay surface and the
soil solution.
It is made up of:
• the permanent negative charge of the clay and
• the cations or counter-ions in the soil solution that balance the negative charge.
The nature and properties of such layers are highly dependent on the type of:
–mineral and
–the chemistry of the pore water.
Diffuse Double Layer

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Diffuse double layer
❑Clay particles have a negative charge
❑Hence, they adsorb cations
❑Under dry conditions, these cations are tightly bound to toclay syrface
by electrostatic force
❑This electrostatic force depends on
•Charge
•Position of charge
•Velanceof the exchangeable
cations

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L5/P16

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L5/P17

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L5/P18

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