18-01-2013, 03:49 PM
LIQUEFACTION OF SOILS
LIQUEFACTION.ppt (Size: 2.5 MB / Downloads: 159)
Introduction
Liquefaction is a process by which saturated soils temporarily loose its strength and behaves like a viscous liquid.
Liquefaction commonly occurs in saturated soils.
Mechanism of Liquefaction
A saturated soil deposits with large contact forces, when pore water pressure is low.
As soil deposits subjected to some rapidly applied loading, the pore water pressure increases.
Water gets trapped and prevent densification.
Increase in pore water pressure reduces the contact force between the soil grains.
Softening and weakening of the soil deposits occurs.
Types Of Ground Failure
Sand boils:-These are formed when sediments that is below the surface has high water content
Lateral spread:-This involves the movement of large blocks of soil.
Horizontal movement of 10 to 15 feet is common.
Build Liquefaction Resistant Structures
A structure that possesses ductility, has the ability to accommodate large deformations and having foundation design that decrease the amount of damage a structure may suffer in case of liquefaction. To achieve these features in a building there are various aspects to consider.
Shallow foundation aspects.
Deep foundation aspects
Deep foundation aspects
It is important that the piles are connected to the cap in a ductile manner that allows some rotation to occur without a failure of the connection. If the pile connections fail, the cap cannot resist overturning moments from the superstructure by developing vertical loads in the piles.
Vibroflotation
Vibroflotation involves the use of a vibrating probe that can penetrate granular soil to depths of over 100 feet. The vibrations of the probe cause the grain structure to collapse thereby densifying the soil surrounding the probe.
Compaction Grouting
In this a slow flowing water/sand/cement mix is injected under pressure into a granular soil. The grout forms a bulb that displaces and hence densifies, the surrounding soil.
Compaction grouting is a good option if the foundation of an existing building requires improvement, since it is possible to inject the grout from the side or at an inclined angle to reach beneath the building.