LiquefactionWhat is soil Liquefaction?

Group Members

Nouman Khadim Warraich

Mirza Farquleet Baig

Haider Ali Rafique

What Is Liquefaction

Liquefaction is the name given to

the process that converts a solid

soil mass into a liquid.

What is Soil Liquefaction

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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October 17, 1989—Soil Liquefaction in the East Bay During the Earthquake

When does it occurs

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

When does it Occurs

Liquefaction occurring beneath buildings and other structures

can cause major damage during earthquakes.

Liquefaction occurs in cohesion less soils (typically those with

a higher content of larger grains such as sand sized) which

have water in the pore spaces, and are poorly drained.

How It Works

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

a reduction in porosity

The pore water which was originally in those spaces

becomes compressed.

increase in pore water pressure).

The pore water pressure becomes so high, that the soil

grains become almost Floats

causing a significant drop in the shear strength

Damages

Liquefied soil, like water, cannot support the weight of whatever is lying

above it – be it the surface layers of dry soil or the concrete floors of

buildings.

The liquefied soil under that weight is forced into any cracks and crevasses

it can find, including those in the dry soil above, or the cracks between

concrete slabs.

It flows out onto the surface as boils, sand volcanoes and rivers of silt. In

some cases the liquefied soil flowing up a crack can erode and widen the

crack to a size big enough to accommodate a car.

How to Identify?

There are a number of different ways to evaluate the liquefaction susceptibility of a soil deposit.

Historical Criteria

Geological Criteria

Compositional Criteria

Historical Criteria

Observations from earlier earthquakes provide a great deal of

information

Soils that have liquefied in the past can liquefy again in future

earthquakes.

If you are building a house and want to find out if your site is

susceptible to liquefaction, you could investigate previous

earthquakes to see if they caused liquefaction at your site.

Information is also available in the form of maps of areas where

liquefaction has occurred in the past and/or is expected to occur in

the future

Geological Criteria

The type of geologic process that created a soil deposit

has a strong influence on its liquefaction susceptibility.

Saturated soil deposits that have been created by

sedimentation in rivers and lakes (fluvial or alluvial deposits),

deposition of debris or eroded material (colluvial deposits),

or deposits formed by wind action (aeolian deposits)

can be very liquefaction susceptible.

Compositional Criteria

Liquefaction susceptibility depends on the soil type.

Clayey soil, particularly sensitive soils, may exhibit strain-

softening behavior similar to that of liquefied soil, but do

no liquefy in the same manner as sandy soils are.

Compositional Criteria

Soils composed of particles that are all about the same size

are more susceptible to liquefaction than soils with a wide

range of particle sizes.

In a soil with many different size particles, the small particles

tend to fill in the voids between the bigger particles thereby

reducing the tendency for densification and pore water

pressure development when shaken.

Types of Failure

Cyclic Mobility

Overturning

Sand Boiling

Cyclic Mobility Deformations due to cyclic mobility develop incrementally because of

static and dynamic stresses that exist during an earthquake.

Lateral spreading, a common result of cyclic mobility, can occur on gently

sloping and on flat ground close to rivers and lakes.

Overturning Liquefaction can cause Overturning of large lateral loads on foundations.

Foundation must also be able to resist horizontal loads bending moments

induced and by lateral movements.

Liquefaction Damage: 1964 Niigata, Japan

Sand Boiling

A sand boil is sand and water that come out onto the ground surface

during an earthquake as a result of liquefaction at shallow depth.

The Damage of Port Structures (at Kushiro Port)

After the earthquake After the earthquake shaking has ceased, and liquefaction effects have

diminished (which may take several hours), the permanent effects include:

Lowering of ground levels where liquefaction and soil ejection has

occurred. Ground lowering may be sufficient to make the surface close to

or below the water table, creating ponds.

Disruption of ground due to lateral spreading.

During And After Earthquake

Solution

To minimize liquefaction, one successful approach id to lower into the

ground, a self digging apparatus till the desired depth is reached; then it is

set in motion vibrating the soil surrounding it. This consolidates the sediment

layer itself, and de-waters it up to the surface.

The ground surface will naturally alter during this process, and the surface is

graded to the desired contours, filled as necessary with overburden, and

smoothed off.

The equipment used at Pegasus Town north of Christchurch New Zealand,

originated from Bahrein, where presumably this is the technique used to

create the 'sand islands'. PAM JAMERA

References

Ambraseys, N., and Sarma, S. (1969). "Liquefaction of Soils Induced by Earthquakes,"

Bulletin of the Seismological Society of America, 59(2), 651-664.

Arulanandan, K., Yogachandran, C., Muraleetharan, K. K., Kutter, B. L., and Chang,

G. S., (1988). "Laboratory Flow Slide During Earthquake Simulation, Centrifuge 88,

Corte, J.-F., ed., Paris, Balkema, Rotterdam, April, pp. 539-544.

Arulanandan, K. and Scott, R. F., Eds. (1993). "Verification of Numerical Procedures for

the Analysis of Soil Liquefaction Problems," Proc. of the Intl. Conference on the

Verification of Numerical Procedures for the Analysis of Soil Liquefaction

Problems, Davis, CA, Balkema Publishers, Rotterdam, Netherlands,

Any Question?