The document discusses soil mechanics topics related to consolidation and settlement. It covers three types of settlement (immediate, primary consolidation, and secondary consolidation). It also explains the fundamental concept of consolidation using a piston-spring model and describes how a one-dimensional consolidation test (oedometer test) is conducted in the laboratory to determine soil compressibility.

1. POWER POINT PRESENTATION
SUBJECT-SOIL MECHANICS
TOPIC-CONSOLIDATION AND SETTLEMENT
OF SOIL

2. Content
-Introduction
-Types of settlement
-Immediate settlement
-Fundamental of consolidation
(piston-spring model)
-One dimensional consolidation
test
-Conclusion

3. Introduction
settlement of soil
SCOPE: This publication concerns (a) immediate settlements, (b) long-term
settlements, (c) rate of settlement, (d) criteria for tolerable settlement, (e)
methods of reducing or accelerating settlements for saturated fine-grained
soils and (f) methods for controlling and/or estimating heave in swelling
soils. Procedures given are for finegrained compressible soils as well as for
coarse-grained soils.
OCCURRENCE OF SETTLEMENTS: The settlement of saturated cohesive soil
consists of the sum of three components; (1) immediate settlement
occurring as the load is applied, (2) consolidation settlement occurring
gradually as excess pore pressures generated by loads are dissipated, and
(3) secondary compression essentially controlled by the composition and
structure of the soil skeleton. The settlement of coarse-grained granular
soils subjected to foundation loads occurs primarily from the compression
of the soil skeleton due to rearrangement of particles. The permeability of
coarse-grained soil is large enough to justify the assumption of immediate
excess pore pressure dissipation upon application of load. Settlement of
coarse-grained soil can also be induced by vibratory ground motion due to
earthquakes, blasting or machinery, or by soaking and submergence.
APPLICABILITY: Settlement estimates discussed in this publication are
applicable to cases where shear stresses are well below the shear strength
of the soil.

4. Consoilidation of soil
The basic understanding of soil consolidation
began with Terzaghi's laboratory tests on soils
and his development of the theory of
consolidation more than seventy years ago.
This fundamental work, first published in
English by Terzaghi (1926) in a series o f
articles in Engineering News-Record, was
more than an explanation o f consolidation; it
was the first statement of the principle of
effective stresses which has dominated soil
mechanics research and practice ever since.

5. Types of settlement
Settlement
Immediate
settlement
Primary
consolidation
settlement
Secondary
consolidation
settlement

6. Immediate settlement
-Caused by the elastic deformation of dry soil
and of moist and saturated soils without any
change in the moisture content in the soil.
-Usually occurred immediately after load is
imposed.
-Completed quickly.
-Constitutes a relatively small amount of total
settlement.
where
q0 = intensity of contact pressure in units of Es
B' = least lateral dimension of contributing base
area in units of Si
I1 and I2 = influence factors, which depend on
L'/B', thickness of stratum H. Poisson's ratio, and
base embedment depth D
Es = average modulus of elasticity of soil laye

9. Primary consoilidation
settlement
CONSOLIDATION SETTLEMENT: For conditions
where excess pore pressures are developed during
the application of load and if preconsolidation
stress is determined reliably, total settlement can
be predicted with reasonable accuracy. The
percentage error is greatest for settlement from
recompression only. In this case an overestimate
may result unless high quality undisturbed samples
are used for consolidation tests.
MAGNITUDE OF CONSOLIDATION SETTLEMENT:
Compute settlement magnitude from change in void
ratio corresponding to change in stress from initial to
final conditions, obtained from the e-log p curve (Figure
3). To improve the accuracy of computations divide the
clay layer into a number of sublayers for computing
settlement. Changes in compressibility of the stratum
and existing and applied stresses can be dealt with more
accurately by considering each sublayer independently
and then finding their combined effect.

10. Secondary consolidation
settlement
->The reduction in volume continues
at a very slow rate even after the
excess pore water pressure
developed by the applied pressure is
fully dissipated and the primary
consolidation is complete.
->This additional reduction in the
volume is known as secondary
consolidation.
->Secondary consolidation becomes
important for certain types of soil,
such as peats and soft organic clays.

11. Fundamental of consolidation
(piston-spring model)
-in this analogy spring act as the soil skeleton.
- while water act as the water in the soil.
-the valve act as the void in the soil which effect the
permeability of the soil.
Valve
Vvvjvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv SPRING
WATER

12. Condition 1
(if load is imposed while the
valve is closed)
 Spring will not
move due to the
incompressibility
of water.
 Therefore, no load
transferred to
spring because it
was all carried by
water.
 This also called the
undrained
condition in soil.
Valve
closed

13. Condition 2
(if load is imposed while the valve
is opened)
 Water were forced
to flow out through
the valve.
 The flow rate
depend to the
diameter of the
hole/valve.
 Some of the load
carried by water
while some were
transferred to the
spring.
 The load increment
to the spring
depend to the
decrease of pore
water pressure.
Valve opened

14. • After all the water
extruded, the load
were totally carried
by spring.
• Deformation
continue to occur
until the spring
reach the final
condition.
• This condition
shows the drained
condition in soil.
No more
water
inside

15. Variation of total stress, pore water pressure and effective stress in a clay layer drained at top
and bottom as the result of an added stress
(Das, 2002)
• At t=0

16. At 0  t  
At t = 

17. One dimensional consolidation
testOedometer test
• Used to determine the compressibility characteristics
of a saturated undisturbed or remolded soil.
• Sample were collected from site.
• Sample is placed in a metal ring.
• Porous disk is placed above and beneath the sample
(to allow water to flow vertically into and out of the
soil sample).
• The sample is immersed in water.

18. • A specific load pressure is applied to the
upper disk (the sample is compressed and
deformation is measured by a dial gauge).
• Dial readings and corresponding time
observations are made and recorded until
deformation has nearly ceased (normally 24
hour).
• Graph is plotted.
• The procedure will be repeated with the
applied pressure doubled from the previous.

19. Typical result of an
oedometer test
• Time-deformation plot : graph with time
along the abscissa (logarithmic scale) and dial
readings along the ordinate (arithmetic
scale).
Stage
2
Stage
3

20.  Pressure-void Ratio Curves : graph with
pressure along the abscissa (logarithmic scale)
and void ratio along the ordinate (arithmetic
scale).
Compression
curve
Rebound
curve
Recompressio
n curve

21. Conclusion
• Conclusion #1
– Settlement of soil can be divided into three
categories (immediate settlement, primary
consolidation settlement, secondary
consolidation settlement).
• Conclusion #2
– Fundamental on consolidation can be further
explain using piston spring model.
• Conclusion #3
– One dimensional test or also known as
oedometer test is a laboratory test to measure
compressibility characteristics of soil.