The document discusses the consolidation process in soil mechanics, which involves the dissipation of excess pore water pressure under static load leading to volume decrease and settlement. It outlines key parameters like the compression index and coefficient of consolidation, as well as methods for measuring and calculating consolidation rates through tests on soil specimens. Applications of consolidation concepts include settlement under foundations and soil stabilization.

1. Soil Mechanics Lab CE
Soil Mechanics Lab CE
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Experiment # 6
Experiment # 6
Consolidation
Consolidation
ASTM D 1883
ASTM D 1883

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Soil Mechanics Lab CE
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Consolidation
Consolidation
 It is the process of gradual
It is the process of gradual
dissipation of excess pore water
dissipation of excess pore water
pressure under static load which is
pressure under static load which is
accompanied by gradual decrease in
accompanied by gradual decrease in
volume of voids (increase in
volume of voids (increase in
settlement).
settlement).

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Settlement
Settlement
 Immediate Settlement
Immediate Settlement
 Consolidation Settlement
Consolidation Settlement time
settlemen
t
time
settlemen
t

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spring
water
P
P
@t=o
σ=P/A
Total stress
u=P/A
Pore water pressure
σ’=0
Strength of the
spring
@t=t
σ=P/A
u=P/A-Δσ
σ’= Δσ
@t=∞
σ=P/A u=0 σ’=σ
The Consolidation Process
The Consolidation Process

5. Soil Mechanics Lab CE
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The Parameters
The Parameters
 Compression Index, C
Compression Index, Cc
c
used to determine the amount of consolidation.
used to determine the amount of consolidation.
 Coefficient of Consolidation, C
Coefficient of Consolidation, Cv
v
used to determine the rate of consolidation.
used to determine the rate of consolidation.

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During consolidation…
During consolidation…
Due to a surcharge q applied
at the GL, the stresses and
pore pressures are increased
at A.
GL
saturated
clay
q kPa
A
σ
u
σ’
GL
saturated clay
q kPa
A
 remains the same (=q)
during consolidation.
u decreases (due to drainage).
’ increases which is the
effective stress carried by the
soil particles,
transferring the load from water
to the soil.
σ=q
u= σ -Δσ
σ’= Δσ

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Consolidation Test
Consolidation Test
fiel
d
GL
lab
undisturbed soil
specimen
Dia = 75 mm
Height = 20 mm
metal ring
(oedometer)
porous
stone
9P
P
= 9P/A ≈ 20kpa
For the first day
Plate load
dial
gauge

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Date,
pressure
Time
Elapsed
time, min.
Dial
reading,
div.
Temp.
C
Date,
pressure
Time
Elapsed
time, min.
Dial
reading,
div.
Temp.
C
Remarks:

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400
420
440
460
480
500
520
540
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0.1 1 10 100 1000 10000
Dial
Reading
(div)
Time (min) - log Scale
Logarithm of time curve fitting
t1 t2= 4t1
1
2
3
5
4
X
6
X
7
8
d50
9
d0
d100
t50
10
11
d50=(d0+d100)/2
Immediate Settlement
Primary
Consolidation
Secondary Consolidation
di = Reading @ t=0

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Calculate C
Calculate Cv50
v50
50
2
d
v
v50
t
H
T
C 
Tv = time factor
= 0.197 for 50% consolidation
Hd =average length of largest drainage path during the given loading increment.
= H for one way drainage.
= H/2 for 2-way drainage.
H = H0 – d50*C
t50 = time elapsed corresponding to d50

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Plot of Vertical Displacement vs. Time
400
420
440
460
480
500
520
540
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0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00
Time (min
0.5
)
dial
R
ead
in
g
(d
iv)
√t90
1
2
3
4
5
d90
d0
B D
C BD= 0.15 BC
di

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Calculate C
Calculate Cv90
v90
90
2
d
v
v90
t
H
T
C 
Tv = time factor
= 0.848 for 90% consolidation
Hd =average length of largest drainage path during the given loading increment.
= H for one way drainage.
= H/2 for 2-way drainage.
H = H0 – d90*C
t90 = time elapsed corresponding to d90

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To determine C
To determine Cc
c
Vs
Vv
ΔH
Vv
Vs
Water
Solid Solid
Water
s
v
s
v
s
v
0
H
H
H
A
H
A
V
V
e



s
H
H
e




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Pressure, p
Pressure, p
(kpa)
(kpa)
Initial deformation
Initial deformation
dial reading at
dial reading at
beginning of first
beginning of first
loading, d
loading, d0
0 (div.)
(div.)
Deformation dial
Deformation dial
reading
reading
representing 100%
representing 100%
primary
primary
consolidation, d
consolidation, d100
100
(div.)
(div.)
Change in thickness
Change in thickness
of specimen,
of specimen, 
H
H
(mm)
(mm)
Change in
Change in
void ratio
void ratio

e
e
Void ratio, e
Void ratio, e
[e = e
[e = e0
0 
 
e]
e]
(1)
(1) (2)
(2) (3)
(3) (4)=[(3)
(4)=[(3)
(2)]
(2)]
 0.002
0.002 (5)=(4)/H
(5)=(4)/Hs
s (6) = e
(6) = e0
0 –(5)
–(5)
0
0
20
20
40
40
80
80
160
160
320
320
160
160
80
80
40
40
R320
R320
R160
R160
R80
R80
R160
R160
R80
R80
R40
R40





 


s
H
H
e
Loading
Unloading

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Void Ratio Vs. Log Pressure
Void Ratio Vs. Log Pressure
Cc
Cs
c
s
s
c
C
)
10
1
:
5
1
(
C
logP
e
C
logP
e
C








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Applications
Applications
 Settlement under foundations
Settlement under foundations
 Soil Stabilization
Soil Stabilization
 Dealing with ground water control
Dealing with ground water control