In this presentation, following topics are covered:
1- Introduction to soil liquifaction.
2- Causes and effects of soil liquifaction
3- Methods to remove soil liquifaction.
4- Mechanism of soil liquifaction.
5- Conclusion.
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What is Liquefaction?
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A phenomenon whereby a saturated or partially saturated
soil substantially loses strength and stiffness in response to
an applied stress, usually earthquake shaking or other sudden
change in stress condition, causing it to behave like a liquid
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What is Soil Liquefaction?
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Soil Liquefaction a phenomenon whereby saturated or
partially saturated soil substantially losses strength and
stiffness in response to an applied the stress, usually
earthquake shaking or other sudden change in stress
condition.
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Liquefaction of Soil
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Soils behave like a liquid. How and why?
To understand the above phenomenon:
some basics required regarding:
Total stress, (σt)
Pore water pressure (u)
Effective stress (σeff )
σt= σeff + u σeff = σt- u
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When does it occurs??
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When the effective stress of soil is reduced to essentially zero, which
corresponds to a complete loss of shear strength
May be initiated by
– Monotonic Loading
– Cyclic loading
– Shock loadings(EQs)
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Types of Soil Liquefaction
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Types of Liquefaction
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There are two types of soil liquefaction
Flow Liquefaction
Cyclic Liquefaction
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Flow Liquefaction
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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. Residual strength is the strength of a liquefied soil.
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Cyclic Liquefaction
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'Cyclic liquefaction' is the state of soil when large shear strains have
accumulated in response to cyclic loading. This is a soil test-based definition,
usually performed via cyclic triaxial and cyclic direct simple shear.
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Effects of Soil Liquefaction
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Effect of Liquefaction
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The effect of soil like on the built environment can be extremely damaging.
Bridge and large building constructed on pile foundation may lose support
from the adjacent soil and buckle or com to rest at a tilt after shaking.
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Earthquake
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An earthquake is the shaking of the surface of the Earth, resulting
from the sudden release of energy in the Earth's lithosphere that
creates seismic waves. Earthquakes can range in size from those that
are so weak that they cannot be felt to those violent enough to toss
people around and destroy whole cities.
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Earthquake Effect
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The effect of Earthquake include ,but are not limited to, the
following:
Landslides
Fires
Soil Liquefaction
Tsunami
Floods
Human Impact
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Earthquake Effect
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How It Works??
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When the seismic waves pass through the soil, the vibrations cause
the individual grains in the soil to
move around and
re-adjust their positions
This ultimately results in a decrease in volume of the soil mass as
the grains pack more tightly together
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Landslides
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The term landslide or, less frequently, landslip, refers to
several forms of mass wasting that include a wide range of
ground movements, such as rock falls, deep-seated slope
failures, mudflows and debris flows.
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Tsunami
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A tsunami or tidal wave, also known as a seismic sea wave, is
a series of waves in a water body caused by the displacement
of a large volume of water, generally in an ocean or a large
lake. Earthquakes, volcanic eruptions and other underwater
explosions
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Method To Reduce Soil Liquefaction
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Providing Deep Foundations
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The structures should be supported on deep foundations such
as piles, that extend through liquefiable soil to deeper and
stable strata. Since such piles will not be able to resist lateral
loads in the liquefiable soil, other measures should be adopted
to resist lateral loads.
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Compaction of Soil
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Compacting the soil and increasing its relative density. Compaction
is usually done by means of vibratory rollers, compaction piles,
vibroflotation, blasting, etc. The extent to which the compaction
should be done is ascertained by estimating the required SPT No. to
prevent liquefaction for that soil for the design earthquake.
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Grouting the Soil
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In this method, the soil is stabilized by injecting chemicals or cement
grout into the soil. This method is sometimes used at sites where
buildings already exist and other methods cannot be used.
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Shallow Foundation Aspect
it is important that all foundation element in shallow foundation are tied
together to make the foundation move or settlement uniformly, thus decrease the amount of
shear force induced in the structural elements resting upon the foundation
Deep Foundation Aspect
liquefaction can cause large lateral load on pile foundation. pile driven through a weak
potentially soil layer to a stronger layer not only have to carry vertical load from the
superstructure, but must also be able resist horizontal load and bending moments induced
by lateral movement if the weak layer liquefies
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Mechanism of Soil Liquefaction
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Mechanism of Soil Liquefaction
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