soil analysis

1. SIVA 1
Phase Relations
N. Sivakugan
Duration: 6 min 31 s

2. SIVA
Copyright©2001
2
Objectives
To 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
Notation
M = mass or weight
V = volume
s = soil grains
w = water
a = air
v = voids
t = total

3. SIVA
Copyright©2001
3
Definitions
Water 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
M
w =
Expressed as percentage.
Range = 0 – 100+%.
X 100%

4. SIVA
Copyright©2001
4
Definitions
Void 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
V
e =

5. SIVA
Copyright©2001
5
Definitions
Porosity (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
V
n = X 100%
Theoretical range: 0 – 100%

6. SIVA
Copyright©2001
6
Definitions
Degree 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
V
S =
Range: 0 – 100%
X 100%
Dr
y Saturate
d

7. SIVA
Copyright©2001
7
A Simple Example
water
air
soil
In this illustration,
e = 1
n = 50%
S = 50%

8. SIVA
Copyright©2001
8
Definitions
Bulk 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
T
m
V
M
=ρ
Units: t/m3
, g/ml, kg/m3

9. SIVA
Copyright©2001
9
Definitions
Saturated 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

10. SIVA
Copyright©2001
10
Definitions
Dry 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
S
d
V
M
=ρ
Units: t/m3
, g/ml, kg/m3

11. SIVA
Copyright©2001
11
Definitions
Bulk, 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/m3
N/m3
m/s2

12. SIVA
Copyright©2001
Phase Relations
Consider a fraction of the soil where Vs = 1.
soil
air
water
1 Gsρw
Seρw
Se
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:

13. SIVA
Copyright©2001
13
Phase Relations
From the previous definitions,
soil
air
water
1 Gsρw
Seρw
Se
e
Phase Diagram
SS
W
G
Se
M
M
w ==
e
e
V
V
n
T
V
+
==
1

14. SIVA
Copyright©2001
14
Phase Relations
soil
air
water
1 Gsρw
Seρw
Se
e
Phase Diagram
W
S
T
T
m
e
SeG
V
M
ρρ
+
+
==
1
W
S
T
T
sat
e
eG
V
M
ρρ
+
+
==
1
W
S
T
S
d
e
G
V
M
ρρ
+
==
1

15. SIVA
Copyright©2001
15
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.

16. SIVA
Copyright©2001
16
A Suggestion..
If you can remember one thing in
phase relations, that should be ..
1
Gsρw
SeρwSe
e
soil
air
water

17. SIVA
Copyright©2001
17
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