Question

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

(a) 44 days

(b) 55 days

(c) 97 days

(d) 107 days

I had been asked this question during an interview for a job.

The query is from Consolidation Problems topic in division One Dimensional Consolidation of Geotechnical Engineering I

Answer 1

Right choice is (c) 97 days

The explanation is: Given, single drainage for sample and double drainage for field layer,

t1 = 2 0 min

d1 = 24 mm = 2.4 cm

d2 = 2 m = 200cm

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, \(t_2=t_1 (\frac{d_2}{d_1} )^2=20(\frac{200}{2.4})^2=97 \,days.\)