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‫(الخواص األسـاســيـة للـتـربــة(‬
‫)‪(Basic Characteristics of Soil‬‬
 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 earth’s 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.
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.
The Soil Phases Diagram
THE SOIL SYSTEM
“PHASE” DIAGRAM
AIR
WATER
SOIL
SOLIDS
Air pockets
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.
Objectives
To compute the masses (or weights) and
volumes of the three different phases.
Notation
M = mass or weight
V = volume
s = soil grains
w = water
a = air
v = voids
t = total
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Vs
soil
Phase Diagram
Ms
Definitions
Water content (w) is a measure of the
water present in the soil.
MW
w
MS
X 100%
Expressed as percentage.
Range = 0 – 100+%.
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Vs
soil
Phase Diagram
Ms
Definitions
Void ratio (e) is a measure of the void
volume.
VV
e
VS
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Vs
soil
Phase Diagram
Ms
Definitions
Porosity (n) is also a measure of the void
volume, expressed as a percentage.
VV
n
VT
Va
air
Vw
water
Ma=0
Vv
X 100%
Mw
Mt
Vt
Theoretical range: 0 – 100%
Vs
soil
Phase Diagram
Ms
Definitions
Degree of saturation (S) is the percentage
of the void volume filled by water.
VW
S
VV
X 100%
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Range: 0 – 100%
Vs
Dry
soil
Saturated
Phase Diagram
Ms
A Simple Example
In this illustration,
e=1
air
n = 50%
water
S = 50%
soil
Definitions
Bulk density (m) is the density of the soil in the
current state.
MT
m 
VT
Units: t/m3, g/ml, kg/m3
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Vs
soil
Phase Diagram
Ms
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
Definitions
Dry density (d) is the density of the soil in dry
state.
MS
d 
VT
Units: t/m3, g/ml, kg/m3
Va
air
Vw
water
Ma=0
Vv
Mw
Mt
Vt
Vs
soil
Phase Diagram
Ms
Definitions
Bulk, saturated, dry and submerged unit
weights () are defined in a similar manner.
 = g
N/m3
kg/m3
m/s2
Specific gravity of the soil grains (Gs) typically
varies between 2.6 and 2.8.
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