Liquefaction of soil

1. LIQUEFACTION OF
SOIL
SUBMITTED BY:-AKASH KUMAR
UNDER THE GUIDANCE OF
Asst. Prof Dr. SUPRIYA PAL
NATIONAL INSTITUTE OF
TECHNOLOGY
DURGAPUR

2.  During liquefaction the water pressure become high enough to
counteract the gravitational pull on the soil particles and
effectively float or suspend the particles.
 Then soil particle move freely with respect to each other. due to
this the strength of soil decreases and the ability of a soil
deposit to support foundations for buildings and bridge is
reduce.
What is soil liquefaction:- Liquefaction is the phenomena
when there is loss of strength in saturated and cohesion-less
soil because of increased pore water pressures and hence
effective stress is reduce due to dynamic loading.

3.  Flow liquefaction:- Flow
liquefaction is a phenomenon in which the
static equilibrium is destroyed by static or
dynamic loads in a soil deposit with low
residual strength. It occurs when the static
shear stresses in the soil exceed the shear
strength of the liquefied soil.
Loosely packed grains of
soil are held together by
friction. Pore spaces filled
with water.
Shaking destabilizes the
soil by increasing the
space between grains and
soil flow like a liquid.
Soil before
liquefaction
Soil after
liquefaction
Type of liquefaction

4. Cyclic mobility:-Cyclic mobility is a
liquefaction phenomenon, triggered by cyclic
loading, occurring in soil deposits with static
shear stresses lower than the soil strength.
 Deformation due to cyclic mobility develop
incrementally because of static and dynamic
stresses that exist during an earthquake.
Effects of liquefaction
 Loss of bearing strength:-The ground
can liquefy and lose its ability to support
structure.
Lateral spreading:-The ground can
slide down very gentle slopes. It is mainly
caused by cyclic mobility. Lateral spreading
causes damage to foundations of buildings,
pipelines, railway lines and cause shaking at
pile due to increased lateral loads.

5.  Sand boil:-Sand-laden water
can be ejected from a buried
liquefied layer and erupt at the
surface to form sand
volcanoes. The surrounding
ground often fractures and
settles.
 Flow failures:-Flow failures
are the most catastrophic
ground failures caused by
liquefaction. These failures
commonly displace large
masses of soil laterally. Flows
develop in loose saturated
sands or silts on relatively
steep slopes,

6.  Ground oscillation :-Where the ground is flat or the slope is too gentle to allow lateral
displacement, liquefaction at depth may decouple overlying soil layers from the underlying
ground, allowing the upper soil to oscillate back and forth and up and down in the form of
ground waves. These oscillations are usually accompanied by opening and closing of fissures
fracture of rigid structures such as pavements and pipelines.
 Flotation:-Light structure
that are buried in the
ground(like pipeline sewers
and nearly empty fuel tanks)
can float to the surface when
they are surrounded by
liquefied soil.
Manhole Lifted up manhole
 Settlement:-Liquefied ground reconsolidates during an earthquake, the
ground surface may settle and the underlying liquefied soil become more
dense.

7. Methods to reduce liquefaction
 Avoid liquefaction-susceptible soil:-The first possibility is to avoid
construction on liquefaction susceptible soil.
 Build liquefaction-resistant structures:-It may be possible to make the structure
liquefaction resistant by designing the foundation elements to resist the effects of liquefaction .
Structure that possesses ductility, has the ability to accommodate large deformations, adjustable
supports for correction of differential settlements
 Shallow foundation aspects:-It is important that
all foundation elements in a shallow foundation are
tied together to make the foundation move or settle
uniformly, thus decreases the amount of shear force
induced in the structural elements resting upon the
foundation.
 A stiff foundation mat is a good type of shallow
foundation. Which can transfer loads form locally
liquefied zone to adjacent stronger ground. Mat foundation

8. Deep foundation aspect:-
Liquefaction can cause large lateral
loads on pile foundations. Piles driven
through a weak, potentially
Soil layer to a stronger layer not only
have to carry vertical loads form the
superstructure, but must also be able
to resist horizontal loads and bending
moments induced by lateral
movements if the weak layer liquefies.
Piles of larger dimensions and/or
more reinforcement can achieve
sufficient resistance.

9.  Soil improvement techniques against liquefaction:-The main objective
of soil improvement techniques used for reducing liquefaction hazards is to
large increases in pore water pressure during earthquake shaking by improving
the strength, density, and drainage characteristics of soil.
 Vibro-compaction :- Vibro-compaction
involves the use of a vibrating prone that can
penetrate granular soil to depths of over 100
feet. The vibration of the probe cause the
grain structure to collapse thereby densifying
the soil surrounding the probe.

10. Compaction grouting:-Compaction
grouting is a technique whereby a
slow-flowing water/sand/cement mix is
injected into loose sand under high
pressure. Gout does not enter soil
but forms a bulb that compact and
densify the soil by forcing it to occupy
less space.
Dynamic compaction:-
Densification by dynamic compaction
is performed by dropping a heavy
weight of steel or concrete in a grid
pattern form heights of 30 to 100 feet.

11. Stone column:-Stone columns are
columns of gravel constructed in the
ground. Stone columns can be
constructed by the vibro-compation
method. In this approach the steel
casing is driven into the soil and gravel
is filled in from the top and tamped
with a drop hammer as the steel
is successively withdrawn.

12. THANK YOU