Question

In a barrage on pervious foundation, sheet piles are provided both upstream and downstream of the barrage to reduce uplift pressure and to prevent piping. Which one of the following statements is true in this regard?

• A. Compared to downstream sheet pile, the upstream sheet pile is more effective in reducing uplift and piping
• B. Compared to upstream sheet pile, the downstream sheet pile is more effective in reducing uplift and piping
• C. Downstream sheet pile is more effective in reducing uplift while the upstream sheet pile is more effective in reducing piping
• D. Upstream sheet pile is more effective in reducing uplift while the downstream sheet pile is more effective in reducing piping

Answer 1

The correct option is D Upstream sheet pile is more effective in reducing uplift while the downstream sheet pile is more effective in reducing piping

Upstream sheet pile


${\varphi }_{C_1}=100-{\varphi }_E$
${\varphi }_{D_1}=100-{\varphi }_D$

Downstream sheet pile


${\varphi }_E=\frac{1}{\varphi }co{s}^{-1}\left(\frac{\gamma -2}{\gamma }\right)$

${\varphi }_D=\frac{1}{\varphi }co{s}^{-1}\left(\frac{\gamma -1}{\gamma }\right)$

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

${\varphi }_D<50\%$

$So{\varphi }_{D_1}>50\%forallvaluesof\alpha$

For normal range of $0.4<\alpha <0.8$

${\varphi }_E=50\%$

$S0{\varphi }_{C_1}=50\%$

Thus upstream piles are more effective in reducing uplift pressure. While down stream piles are more effective in reducing exit gradient.