Question

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

• A. 1 in 6.0
• B. 1 in 5.0
• C. 1 in 3.4
• D. 1 in 2.5

Answer 1

The correct option is C 1 in 3.4

As per Khosla's method,
Exit gradient,
$G_E=\frac{H}{d}.\frac{1}{\pi \sqrt{\lambda }}$

Where, $\lambda =\frac{1}{2}[1+\sqrt{1+{\alpha }^2}]$

and $\alpha =\frac{b}{d}$

Here, B = 10 m
depth of sheet pile,
d = 4m
Head loss, H = 5m
$\alpha =\frac{10}{4}=2.5$

$\lambda =\frac{1}{2}[1+\sqrt{1+{2.5}^2}]=1.846$

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

$=\frac{5}{4}\frac{1}{\pi \sqrt{1.846}}=0.293=\frac{1}{3.41}$