Question

A 20 m long horizontal concrete floor under a barrage on a permeable foundation retains a 5 m head of water and has a 5 m deep downstream end pile. The exit gradient is

• A. 1 in 4
• B. 1 in 5
• C. 1 in 6
• D. 1 in 8

Answer 1

The correct option is B 1 in 5

$G_E=\frac{H}{d}\times \frac{1}{\pi \sqrt{\gamma }}$

$\gamma =\frac{1+\sqrt{1+{\alpha }^2}}{2}=\frac{1+\sqrt{1+4^2}}{2}=2.56$

$(\therefore \alpha =\frac{b}{d}=\frac{20}{5}=4)$

$G_E=\frac{5}{5}\times \frac{1}{3.15\times \sqrt{2.56}}=\frac{1}{5}$