What is Soil Liquefaction? Types and Features

Soil liquefaction is the phenomenon in which saturated, or partially saturated soil substantially loses strength and stiffness and behaves like a liquid. The soil loses its strength and stiffness in response to applied stress like earthquake shaking or sudden change in stress conditions and generates a quicksand effect.

What is Soil Liquefaction?
What is Soil Liquefaction?

The situation thus will bring effective stress = 0. Here, the soil will behave more like a liquid than like a solid. Hence, the process is called liquefaction.

Soil Liquefaction means, Effective Stress = 0

How Does Soil Liquefaction Work?

The soil in its normal condition is a mixture of soil particles that stay together, resting one over the other due to gravity in the form of grids. Each soil particle has its own contact force that hold all the individual particles in place.

What is Soil Liquefaction? Importance in Construction

When this soil is subjected to sudden or rapid loading, it loses its cohesive strength and gets softened, weak, and loses its solid properties. This would make soil lose its solid properties and get converted to liquid properties. Before the action of earthquake forces, the water pressure within the soil is very less. The earthquake shaking causes the water pressure to increase to a point where the soil particles can move with respect to each other, similar to a liquid behavior.

Features of Soil Liquefaction

Liquefaction is the main phenomenon responsible for a tremendous amount of damage due to earthquakes around the world. Some of the features of soil liquefaction are:
  1. Liquefaction mainly occurs in saturated soils.
  2. Liquefaction generates a quicksand effect, due to which the constructed structure gets pulled into the diluted soil leading to the leaning and collapse of the structure.
  3. Liquefaction of soil causes sudden movement shift that is out of sync with the rest of the structure which can cause damage to the property leading to casualties.
  4. Soil liquefaction decreases the strength of the soil and its ability to support the foundation for the buildings & bridges.
  5. Liquefied soil exerts pressure on retaining walls, causing its overturning or tilting.
  6. Liquefaction increases water pressure which triggers landslides and causes the collapse of dams.

Types of Soil Liquefaction 

The two types of liquefaction are:
  1. Flow Liquefaction
  2. Cyclic Mobility

Flow Liquefaction

In this type of liquefaction, the static equilibrium is destroyed by the static or dynamic loads in a soil deposit with low residual strength. This occurs when

Static shear stress in the soil > Shear strength of the liquefies soil.

Cyclic Mobility

Soil liquefaction that is triggered by cyclic loading, occurs in soil deposits with 
Static shear stresses < Soil Strength

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