Question

A gravity dam profile is as shown in figure

If the water on the downstream is completely removed, the uplift force will_______
(Assume unit weight of water = $10kN/m^3$)

• A. increase by 120 kN/m
• B. decrease by 40 kN/m
• C. decrease by 600 kN/m
• D. increase by 400 kN/m

Answer 1

The correct option is C decrease by 600 kN/m

Uplift force,
$U_1=\left[\frac{{\gamma }_w{h}_1+{\gamma }_w{h}_2}{2}\right]\times B$

$=\frac{(10\times 40)+(10\times 4)}{2}\times 30$

$=6600kN/m$

If d/s water is removed,


Uplift force,
$U_2=\frac{1}{2}\times {\gamma }_w{h}_1\times B$
$=\frac{1}{2}\times 10\times 40\times 30$
$=6000kN/m$

Then uplift force will decrease by 600 kN/m