Question

Uplift force acting on a gravity dam having height $H_1$ and water level on upstream side and downstream side as $h_1$ and $h_2$ metres is $U_1$. Another gravity dam of same slope and construction material is having a height of 1.2 times $H_1$; but has the same water levels $h_1$ and $h_2$ as that of first gravity dam. If the uplift force acting on the second gravity dam is $U_2$, which of the following relationships will be correct?
(assume base width is same for both dams)

• A. $U_2=1.2U_1$
• B. $U_2=1.44U_1$
• C. $U_2=0.8U_1$
• D. $U_2=U_1$

Answer 1

The correct option is D $U_2=U_1$


$\text{uplift force}=\left[\frac{C{\gamma }_w{h}_1+C{\gamma }_w{h}_2}{2}\right]\times B$
where,
$C:\text{uplift pressure coefficient}$
${\gamma }_w:\text{unit weight of water}$
$h_1,h_2:\text{height of water on u/s and d/s sides}$
$B:\text{base width}$

It is independent of height of dam but increase in height of dam will increase the net downward vertical force.