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UPSC Civil Service Exam Questions - Engineering

Q1:

In a three-layered soil, water flows parallel to stratification. The thickness of the middle layer is twice that of top and bottom layer. The coefficient of permeability of middle layer (2K) is twice that of top and bottom layer (K). What is the average coefficient of permeability for this flow ?

A K

B 1.33 K

C 1.5 K

D 0.66 K

ANS:C - 1.5 K

first layer=k(1)=k.
second layer=k(2)=2k(given).
third layer=k(3)=k.

first layer thickness=H.
second layer thichness=2H.
third layer thickness=H.

Average(k) = k * H+2k*2H+k*H/H+2H+H=1.5k.