What is the science behind Quick Sand?

Some may think that "Quick sand" is the type of sand. But it is not. It is the hydraulic condition of sand. 

When the flow of water takes place in an upward direction, the seepage pressure also acts in the upward direction and the effective pressure is reduced. If seepage pressure becomes equal to the total pressure due to the submerged weight of soil, the effective pressure reduced to zero. In such a case, a cohesionless soil loses all its shear strength and the soil particles have a tendency to move up in the direction of flow. This phenomenon of the lifting of soil particles is called quick condition or boiling condition or quick sand.

-Quick condition mainly occurs in fine sands. For clays, the shear strength of soil does not reduce to zero even when effective stress becomes zero, due to its cohesion. Hence, quick sand condition does not occur in clays. 

-During quick condition, the hydraulic gradient becomes critical, i.e. i_c = 1.

Where it can occur? 

-Downstream of Dam site due to high artesian pressure.
-An excavation into the sand below groundwater table where water is pumped out to work in dry condition etc.

How to prevent it?     

-Lowering water table in the area

-keeping the certain depth of water in excavation trenches