Question

A weir on a permeable foundation with downstream sheet pile as shown in the figure below. The exit gradient as per Khosla's methods is

• A. 1 in 5.0
• B. 1 in 3.33
• C. 1 in 6.67
• D. 1 in 4.5

Answer 1

The correct option is B 1 in 3.33

The exit gradient may be given as,

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

Where,
$\lambda =\frac{1+\sqrt{1+{\alpha }^2}}{2}\text{and}\alpha =\frac{b}{d}$

Here, b = 10 m, d = 5 m, H = 6 m

$\alpha =\frac{b}{d}=\frac{10}{5}=2$

$\text{and}\lambda =\frac{1+\sqrt{1+4}}{2}=1.618$

$G_E=\frac{6}{5}\times \frac{1}{\pi \sqrt{1.618}}$

$=0.30=\frac{1}{3.33}$

1 in 3.33