Post on 13-Jul-2015
1SIVA
Phase RelationsN. 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
Copyright©2001
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
Copyright©2001
A Simple Example
water
air
soil
In this illustration,
e = 1
n = 50%
S = 50%
8SIVA
Copyright©2001
DefinitionsBulk density (ρm) 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=ρ
Units: t/m3, g/ml, kg/m3
9SIVA
Copyright©2001
DefinitionsSaturated density (ρsat) is the density of the soil
when the voids are filled with water.
Submerged density (ρ’) is the effective density of the soil when it is submerged.
ρ’ = ρsat - ρw
10SIVA
Copyright©2001
DefinitionsDry density (ρd) 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=ρ
Units: t/m3, g/ml, kg/m3
11SIVA
Copyright©2001
DefinitionsBulk, saturated, dry and submerged unit weights (γ)
are defined in a similar manner.
γ = ρg
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 V s = 1.
soil
air
water
1 Gsρw
SeρwSe
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
Copyright©2001
Phase RelationsFrom the previous definitions,
soil
air
water
1 Gsρw
SeρwSe
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 Gsρw
SeρwSe
e
Phase Diagram
WS
T
Tm e
SeG
V
M ρρ++==1
WS
T
Tsat e
eG
V
M ρρ++==
1
WS
T
Sd e
G
V
M ρρ+
==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 ..
1Gsρw
SeρwSe
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