A coarse-grained soil has a voids ratio 0.75, and specific gravity as 2.75. The critical gradient at which quick sand condition occurs, is

A sand soil becomes a ‘quicksand’ when this flow is upward under the hydraulic gradient that reduces the effective stress down to zero. In a typical sand soil condition, the critical hydraulic gradient is of the ratio 1: 4. The Quick Sand condition occurs mainly in fine sand conditions.