GATE Civil Engineering (CE) 2018 Shift 2 Solved Paper

Question : 28 of 65

Marks: +1, -0

A flownet below a dam consists of 24 equipotential drops and 7 flow channels. The difference between the upstream and downstream water levels is

6 {m}

. The length of the flow line adjacent to the toe of the dam at exit is

1 {m}

. The specific gravity and void ratio of the soil below the dam are

2.70

and

0.70

, respectively. The factor of safety against piping is

Solution:

N_{t}=7 N_{d}=24 \;\; H=6 {m}

Critical Hydraulic Gradient

i_{c}=\;{G-1}/{1+e}=\;{2.7-1}/{1+0.7}=1

Exit Gradient

(i_{\;\text "ext "\;})=\;{∆ h}/{l}=\;{({H}/{N_{d}})}/{l}=\;{({6}/{24})}/{1 {m}}=\;{1}/{4}

{F.O} . {S} .=\;{i_{c}}/{I_{\;\text "exit "\;}}=\;{1}/{(\;{1}/{4})}=4

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