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Safe Depth of Excavation

At a construc...

Question

At a construction site, a contractor plans to make an excavation as shown in the figure.

The water level in the adjacent river is at an elevation of + 20.0 m. Unit weight of water is 10 KN/ $m^{3}$ . The factor of safety (upto decimal places) against sand boiling for the proposed excavation is
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Solution

The correct option is A 1
$F O S = \frac{B u o y a n t w e i g h t}{S e e p a g e f o r c e}$

$F O S = \frac{γ_{s u b} \times 10}{10 \times γ_{w}} = \frac{20 - 10}{10} = 1$

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