consolidation of soil :-introduction

2.  Consolidation is a process by which soils decrease in volume.
 According to Karl Terzaghi "consolidation is any process which involves
decrease in water content of a saturated soil without replacement of
water by air.”
 Reduction in volume takes place by expulsion of water under long
term static loads. It occurs when stress is applied to a soil that causes
the soil particles to pack together more tightly, therefore reducing its
bulk volume.
 When this occurs in a soil that is saturated with water, water will be
squeezed out of the soil.

3. When a saturated clay is loaded externally,
saturated clay
GL
the water is squeezed out of the clay over
a long time (due to low permeability of
the clay).

4. This leads to settlements occurring over a long
time,
time
settlement
which could be several years.

5. -Lowering of the ground water table
-External static loads from structures
-Self weight of recently placed soils
-Desiccation

6.  The consolidation of a soil deposit can be divided into
3 stages :
(1) Initial consolidation
(2) Primary consolidation
(3) Secondary Consolidation

7.  After initial consolidation, further reduction in volume
of soil mass occurs due to expulsion of water from
voids. This is known as primary consolidation.
 In fine grain soils, the primary consolidation occurs,
over a long time.
 On the other hand, in coarse grained soils , the
primary consolidation occurs rather quickly due to
high permeability .

8.  When a load is applied to a partially saturated soil, a
decrease in volume occurs due to expulsion and
compression of air in the voids.
 A small decrease in volume also occurs due to
compression of solid particles .
 The reduction in volume of the soil just after the
application of the load is known as initial
consolidation.

9.  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.

10.  Process of reduction of
volume under sustained,
static loading.
 It causes reduction in
volume of a saturated
soil due to squeezing out
of water from soil.
 It is a rapid process of
reduction of volume by
mechanical process such
as rolling, tamping.
 The volume of partially
saturated soil decrease
because of expulsion of
air from the voids at the
unaltered water content.

11.  It is a process which
occurs in nature when
the saturated soil
deposits are subjected to
static load caused by the
weight of the buildings &
other structures.
 It is artificial process
which is done to increase
the density of the soil to
improve its properties
before it is put to any
use.

12. Several works in the field show
that a temperature increase
induces firstly an increase of
the permeability and secondly,
for normally consolidated
states, an irreversible
contraction and a modification
of the yield limit. These results
point to the fact that a
temperature increase could
lead to an increase of the
settlement rate and an increase
of the final value of settlement.
This figure shows two kinetics of consolidation process obtained at 25
and at 60°C