GATE 2017 CE (CE1) – Question 32

Geotechnical Engineering · Compaction and one-dimensional consolidation · 1 mark · Numerical answer

A 3 m thick clay layer has an initial uniform excess pore pressure of 145 kPa, drains into sand above, and rests on an impermeable stratum. The coefficient of consolidation is $c_v=3.0$ mm²/min and $T_v(90)=0.85$. Find the time for 90% consolidation in days, rounded to the nearest integer.

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Correct answer: 1765 to 1775

Explanation

Only the upper boundary drains, so the drainage path is the full layer thickness, $H_d=3000$ mm. Use $T_v=c_vt/H_d^2$: $t=0.85(3000)^2/3=2550000$ min. Dividing by $60\times24$ gives 1770.833 days, which rounds to 1771. The initial pressure magnitude cancels because the requested degree of consolidation is a fraction.

GATE 2017 CE (CE1) – Question 32

Explanation

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