Question

The coefficient of permeability of the two soil layers 1 and 2 in soil deposit is 9*10^-7 cm/s and 4*10^-7 cm/s respectively. The thickness of the layers is equal. The value of average permeability parallel to bedding planes is ________

(a) 4.5*10^-7 cm/s

(b) 5.5*10^-7 cm/s

(c) 6.5*10^-7 cm/s

(d) 7.5*10^-7 cm/s

The question was asked in examination.

I'm obligated to ask this question of Permeability of Stratified Soil Deposits in chapter Permeability of Geotechnical Engineering I

Answer 1

Right option is (c) 6.5*10^-7 cm/s

Easy explanation: Given,

K1=9*10^-7 cm/s

K2=4*10^-7 cm/s

Let the thickness of each layer be z,

Therefore the total thickness is 2z.

For flow parallel to the bedding plane,

\(K_x=\frac{k_1 z_1+k_2 z_2+⋯.+k_n z_n}{z} \)

\(K_x=\frac{z*9*10^{-7}+ z*4*10^{-7}}{2z} \)

∴ Kx=6.5*10^-7 cm/s.