Soil Liquefaction :
It can be defined as:
“Conversion of soil into fluid like mass during an earthquake or other seismic event.”
When a saturated loose sand deposit is subjected to load of very short duration, such as occurs during earthquakes. Then water does not find time to escape through the pores. It results in increase of pore water pressure. Since the total stresses have not increased during loading, the effective stresses tend toward zero. The soil loses all strength and bearing capacity. This phenomenon is known as soil liquefaction.
Normally, under static loading, the sand has sufficient permeability so the water can escape and pore water pressure can dissipate. But in this case water does not find time to escape through pores. The increase in pore water pressure and decrease in effective stresses causes the soil to fail.
Casagrande was the first to explain liquefaction and described some spontaneous failures caused by liquefaction.