siva 1 phase relations n. sivakugan duration: 6 min 31 s
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1SIVA
Phase Relations
N. Sivakugan
Duration: 6 min 31 s
2SIVA
Copyright©2001
ObjectivesTo compute the masses (or weights) and
volumes of the three different phases.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
Phase Diagram
NotationM = mass or weightV = volumes = soil grainsw = watera = airv = voidst = total
3SIVA
Copyright©2001
DefinitionsWater content (w) is a measure of
the water present in the soil.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
Phase Diagram
S
W
M
Mw
Expressed as percentage.
Range = 0 – 100+%.
X 100%
4SIVA
Copyright©2001
DefinitionsVoid ratio (e) is a measure of the
void volume.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
Phase Diagram
S
V
V
Ve
5SIVA
Copyright©2001
DefinitionsPorosity (n) is also a measure of the void
volume, expressed as a percentage.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
Phase Diagram
T
V
V
Vn X 100%
Theoretical range: 0 – 100%
6SIVA
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DefinitionsDegree of saturation (S) is the percentage
of the void volume filled by water.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
Phase Diagram
V
W
V
VS
Range: 0 – 100%
X 100%
Dry Saturate
d
7SIVA
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A Simple Example
water
air
soil
In this illustration,
e = 1
n = 50%
S = 50%
8SIVA
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DefinitionsBulk density (m) is the density of the soil
in the current state.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
Phase Diagram
T
Tm V
M
Units: t/m3, g/ml, kg/m3
9SIVA
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DefinitionsSaturated 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
10SIVA
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DefinitionsDry density (d) is the density of the soil in
dry state.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
Phase Diagram
T
Sd V
M
Units: t/m3, g/ml, kg/m3
11SIVA
Copyright©2001
DefinitionsBulk, saturated, dry and submerged unit
weights () are defined in a similar manner.
= g
Here, use weight (kN) instead of mass (kg).
Specific gravity of the soil grains (Gs) typically varies between 2.6 and 2.8.
kg/m3N/m3 m/s2
SIVA
Copyright©2001
Phase RelationsConsider a fraction of the soil where Vs = 1.
soil
air
water
1 Gsw
SewSe
e
Phase Diagram
The other volumes can be obtained from the previous definitions.
Mass = Density x Volume
volumes masses
The masses can be obtained from:
13SIVA
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Phase RelationsFrom the previous definitions,
soil
air
water
1 Gsw
SewSe
e
Phase Diagram
SS
W
G
Se
M
Mw
e
e
V
Vn
T
V
1
14SIVA
Copyright©2001
Phase Relations
soil
air
water
1 Gsw
SewSe
e
Phase Diagram
WS
T
Tm e
SeG
V
M
1
WS
T
Tsat e
eG
V
M
1
WS
T
Sd e
G
V
M
1
15SIVA
Copyright©2001
Try not to memorise the equations. Understand the definitions, and develop the relations from the phase diagram with VS = 1;
Assume GS (2.6-2.8) when not given;
Do not mix densities and unit weights;Soil grains are incompressible. Their mass and volume remain the same at any void ratio.
16SIVA
Copyright©2001 A Suggestion..
If you can remember one thing in phase relations, that should be ..
1Gsw
SewSe
e
soil
air
water
17SIVA
Copyright©2001
Testing Times…State whether the following are true or false?
(a) Dry density is greater than submerged density
(b) In unsaturated soils, water content is always less than 100%.
(c) Larger the void ratio, larger the porosity.
True
False
True