Soil Mechanics A

1
ONE DIMENSIONAL
SETTLEMENT BEHAVIOUR
2
Embankment loading on a layered soil
Embankment
x
Soil layer 1
z
Soil layer 2
Rock
3
Embankment loading on a layered soil
If the embankment is wide compared to the depth
of the soil layer then the restraining effect of
adjacent columns of soil prevents horizontal
movement. Thus there is vertical strain but no
horizontal strain
Before loading
After loading
4
Example of a large loaded area, conditions
beneath approximately 1-D
5

6
Measurement of soil properties
The oedometer apparatus
Load
Displacement measuring device
Cell
Loading cap
water
Soil sample
Porous disks
7
Relation between axial and volume strain
(a) Before Deformation
(b) After Deformation
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Relation between axial and volume strain
(a) Before Deformation
(b) After Deformation
(1)
Volume strain
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Relation between axial and volume strain
(a) Before Deformation
(b) After Deformation
(1)
Volume strain (a)
V Vo Dx Dy Dz
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Relation between axial and volume strain
(a) Before Deformation
(b) After Deformation
(1)
Volume strain (a)
V Vo Dx Dy Dz (b)
(2a)
11
Relation between axial and volume strain
(2b)
12
Relation between axial and volume strain
(2b)
(2c)
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Relation between axial and volume strain
(2b)
(2c)
Neglecting second and higher order terms
(2d)
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Relation between axial and volume strain
(2b)
(2c)
Neglecting second and higher order terms
(2d)
For confined compression this becomes
(2e)
15
Relation between volume strain and voids ratio
Voids
Vse0
Solid Material
Vs
Vs
(a) Before Deformation
(b) After Deformation
16
Relation between volume strain and voids ratio
Voids
Vse0
Solid Material
Vs
Vs
(a) Before Deformation
(b) After Deformation
17
Relation between volume strain and voids ratio
Voids
Vse0
Solid Material
Vs
Vs
(a) Before Deformation
(b) After Deformation
18
Relation between volume strain and voids ratio
19
Relation between volume strain and voids ratio
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Relation between volume strain and voids ratio
(3a)
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Relation between volume strain and voids ratio
(3a)
For confined compression ezz ev
(2e)
(3b)
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One dimensional soil behaviour
A
2
Voids ratio, e
C
B
1
D
Log 10 (effective stress, s)
23
Terminology

• Preconsolidation stress (pressure)
• The maximum effective stress which has been
  applied to an element of soil

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Terminology

• Preconsolidation stress (pressure)
• The maximum effective stress which has been
  applied to an element of soil
• Over - consolidated
• A soil is called over-consolidated (OC) if

lt
Current Effective Stress
Preconsolidation Stress
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Terminology

• Preconsolidation stress (pressure)
• The maximum effective stress which has been
  applied to an element of soil
• Over - consolidated
• A soil is called over-consolidated (OC) if
• Normally consolidated
• A soil is called normally consolidated (NC) if

lt
Current Effective Stress
Preconsolidation Stress

Current Effective Stress
Preconsolidation Stress
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Terminology
It is not possible for
gt
Current Effective Stress
Preconsolidation Stress
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Terminology
It is not possible for
gt
Current Effective Stress
Preconsolidation Stress
e
Impossible states
Normal Consolidation Line
Over-consolidated states
log10 (s)
28
Normally consolidated soil
Deposition
P
Loading
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Over - consolidated soil
O
Q
e e0 e ef
F
P
R
logarithmic scale
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Over - consolidated soil
(5)
Overconsolidation ratio,
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Estimating the preconsolidation pressure
e
A
B
log (s)
Casagrandes method
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Estimating the preconsolidation pressure
e
C
A
B
log (s)
Casagrandes method
33
Estimating the preconsolidation pressure
D
e
C
A
B
log (s)
Casagrandes method
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Estimating the preconsolidation pressure
D
e
C
A
F
E
B
log (s)
Casagrandes method
35
Estimating the preconsolidation pressure
D
e
C
A
F
E
B
log (s)
Casagrandes method
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Idealised 1-D soil behaviour
e
log (s)
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Idealised normally consolidated response
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Idealised normally consolidated response
Slope of IF
(6a)
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Idealised normally consolidated response
Slope of IF
(6a)
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Idealised normally consolidated response
Slope of IF
(6a)
(6b)
- Cc
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Idealised normally consolidated response
Slope of IF
(6a)
(6b)
- Cc
(6c)
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Idealised over - consolidated response
Slope of IF
(7a)
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Idealised over - consolidated response
Slope of IF
(7a)
(7b)
- Cr
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Idealised over - consolidated response
Slope of IF
(7a)
(7b)
- Cr
(7c)
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Voids ratio change for soil moving from OC to NC
(1)
e1
(2)
e2
e3
(3)
46
Voids ratio change for soil moving from OC to NC
(1)
e1
(2)
e2
e3
(3)
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Voids ratio change for soil moving from OC to NC
(1)
(8a)
e1
(2)
e2
e3
(3)
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Voids ratio change for soil moving from OC to NC
(1)
(8a)
e1
(2)
e2
(8b)
e3
(3)
49
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