Quick sand condition occurs when

1. The void ratio of the soil becomes 1.0
2. The upward seepage pressure in soil becomes zero
3. The upward seepage pressure in soil becomes equal to the saturated unit weight of the soil.
4. The upward seepage pressure in soil becomes equal to the submerged unit weight of the soil.

At quick sand conditions, upward seepage pressure = downward submerged unit weight of soil i.e., effective stress = 0