Question

A clay sample in laboratory test has 24mm thickness. It is tested with double drainage and consolidated 50%. The clay layer from which sample was obtained is 4m thick. Find the time to consolidate 50% with single drainage.

(a) 1544 days

(b) 1455 days

(c) 1322 days

(d) 1799 days

I have been asked this question during an internship interview.

I'd like to ask this question from Consolidation Problems in division One Dimensional Consolidation of Geotechnical Engineering I

Answer 1

The correct choice is (a) 1544 days

Explanation: Given, double drainage for sample and single drainage for field layer,

t1=20 min

d1=24 mm/2 = 2.4 cm/2 = 1.2 cm

d2 = 4 m = 400cm

Since, for same degree of consolidation of 50%, Tv is same,

\(t∝\frac{d^2}{C_r}\)

Therefore, \(\frac{t_2}{t_1} =(\frac{d_2}{d_1} )^2\)

So, \(t_2=t_1 (\frac{d_2}{d_1} )^2=20(\frac{400}{1.2})^2=1544 \,days.\)