A stratum of clay 2 m thick will get consolidated 80% in 10 years. For the 80% consolidation of 8 m thick stratum of the same clay, the time required is

ANS:D - 160 years

Drainage path will be 4 times.
(t1/t2) = sq(d1)/sq(d2).
t1 = sq(4)*10/sq(1).
t1 = 160 yrs. Since the percentage of consolidation is same. using this formula fetches you the solution.

T1/T2=[(D2)^2] / [(D1)^2].
T=time taken to consolidate a stratum of soil of thickness D,
T1/10=[(8)^2] / [(2)^2)],
T1=10*64/4=160. .8 x 10/1 = 8.
tv = 8.
.8 x t/16 = 8.
t = 160. Time factor T = Cv*t/h^2.

T = 80*10/2^2 = 200.

For h= 8 m.

T = 80*t/8^2 => 200*64/80 = t.

=> t = 160 years.