(Basic Characteristics of Soil)

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((?????? ???????????? ?????????? (Basic
Characteristics of Soil)
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• Soil and Soil Engineering

• The term Soil has various meanings depending
  upon the general field in which it is being
  considered.
• To a Pedologist (agricultural soil
  scientist)... Soil is the substance existing on
  the earth's surface, which grows and develops
  plant life.
• To a Geologist ..... Soil is the material in
  the thin surface zone within which roots occur,
  and all the rest of the earths crust is termed
  ROCK irrespective of its hardness.

To an Engineer .... Soil is the un-cemented
deposits of mineral and/or organic particles or
fragments covering large portion of the earth's
crust.
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Ingredients of Soil The nature of soil differ
from other material, since it composes from three
states and they respectively as follows Solid
State, Liquid State, and Gas State.
The Phase Diagram
In a typical volume of soil there are three
components are arranged in a complex mixture
Soil Solids, Water, and Air. To visualize the
relationships among the components when
performing weight-volume or mass-volume
calculations, drawing a phase diagram is
recommended. Much like checking equilibrium with
a free body diagram in statics, completing and
balancing a phase diagram with numerical values
of all quantities permits crosschecking the
solution. The Figure below shows an element of
soil and the corresponding phase diagram.
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The Soil Phases Diagram
PHASE DIAGRAM
THE SOIL SYSTEM
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All solid particles in the element are taken as
an equivalent single mass at the bottom of the
diagram. Above the solids is the water-also
represented as a single equivalent mass-and above
that, the air. On the sides of the diagram are
variable names numerical values are entered here
during calculations. On the left side are the
total volume V, the volume of solids Vs, the
volume of water Vw, and the volume of air Va. The
combined volume of water and air is the volume of
voids Vv . On the right side are shown the total
weight M, the weight of solids Ms, and the weight
of water Mw. The weight of air is negligible.
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Objectives

• To compute the masses (or weights) and volumes of
  the three different phases.

NotationM mass or weight V volume s soil
grains w water a airv voidst total
Phase Diagram
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Definitions

• Water content (w) is a measure of the water
  present in the soil.

X 100
Expressed as percentage.
Range 0 100.
Phase Diagram
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Definitions

• Void ratio (e) is a measure of the void volume.

Phase Diagram
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Definitions

• Porosity (n) is also a measure of the void
  volume, expressed as a percentage.

X 100
Theoretical range 0 100
Phase Diagram
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Definitions

• Degree of saturation (S) is the percentage of the
  void volume filled by water.

X 100
Range 0 100
Dry
Saturated
Phase Diagram
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A Simple Example
In this illustration,
e 1
n 50
S 50
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Definitions

• Bulk density (?m) is the density of the soil in
  the current state.

Units t/m3, g/ml, kg/m3
Phase Diagram
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Definitions

• Saturated density (?sat) is the density of the
  soil when the voids are filled with water.

Submerged density (?) is the effective density
of the soil when it is submerged.
? ?sat - ?w
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Definitions

• Dry density (?d) is the density of the soil in
  dry state.

Units t/m3, g/ml, kg/m3
Phase Diagram
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Definitions

• Bulk, saturated, dry and submerged unit weights
  (?) are defined in a similar manner.

? ?g
Specific gravity of the soil grains (Gs)
typically varies between 2.6 and 2.8.
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Testing Times
State whether the following are true or false?
(a) Dry density is greater than submerged density
True
(b) In unsaturated soils, water content is always
less than 100.
False
(c) Larger the void ratio, larger the porosity.
True
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