Question

A stratum of soil consists of three layers of equal thickness. The permeability of both the top and the bottom layers is 10${}^{-4}$cm/s; and that of the middle layer is 10${}^{-3}$ cm/s; then the value of the horizontal coefficient of permeability for the entire composite of the soil layers is

• A. $2\times {10}^{-4}cm/s$
• B. $3\times {10}^{-4}cm/s$
• C. $4\times {10}^{-4}cm/s$
• D. $5\times {10}^{-4}cm/s$

Answer 1

The correct option is C $4\times {10}^{-4}cm/s$

$k_H=\frac{k_{1}H+k_{2}H+k_{3}H}{3H}$

$=\frac{{10}^{-4}+{10}^{-3}+{10}^{-4}}{3}$

$=\frac{12\times {10}^{-4}}{3}=4\times {10}^{-4}cm/s$