GATE Civil Engineering (CE) 2021 Shift 2 Solved Paper

A water filtration unit is made of uniform-size sand particles of 0.4 mm diameter with shape factor of 0.84 and specific gravity of 2.55. The depth of the filter bed is 0.70 m and the porosity is 0.35. The filter bed is to be expanded to a porosity of 0.65 by hydraulic backwash. If the terminal settling velocity of sand particles during during backwash is 4.5 cm/s, the required backwash velocity is