A 5 m thick soil stratum has coefficient of permeability of 3 × 10-7 m/sc. A separate test conducted on the soil sample gave porosity value of 40% and bulk unit weight of 21 kN/m3 at a moisture content of 30%. The head at which the upward seepage will cause quick sand condition (in meter) is __________.
Enter numerical value using the virtual keypad. Round off where necessary.