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GATE 2020 CE (CE2) – Question 57

Geotechnical Engineering · Permeability and seepage: flow nets, uplift pressure, piping, capillarity · 2 marks · Numerical answer

A constant-head permeability test has gradient 2.5. Soil specific gravity is 2.65 and saturated water content 20%. Permeability is 0.1 cm/s. Find seepage velocity (cm/s), to two decimals.

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Correct answer: .7 to .73

Explanation

At saturation, $e=wG_s=0.2(2.65)=0.53$ and $n=e/(1+e)=0.346405$. Darcy velocity is $ki=0.25$ cm/s. Pore velocity is $ki/n=0.721698$, or **0.72 cm/s**.