Question

Which are the factors that affect the permeability of soil?

(i) Particle size

(ii) Void ratio

(iii) Degree of saturation

(iv) Adsorbed water

1. (i) and (ii) 
2. (i), (ii) and (iii)
3. (ii) and (iv) 
4. (i), (ii), (iii) and (iv)

Answer 1

Correct Answer - Option 4 : (i), (ii), (iii) and (iv)

Explanation

Permeability depends on both soil properties and Fluid properties

The kozney – Carman equation is quite useful, it reflects the effect of factors that affect permeability

\(k = \frac{{{\gamma _w}}}{\mu } \times \frac{{{e^3}}}{{1 + e}} \times D_{10}^2\)

Where,

D10 is effective grain size

e is the void ratio

μ is viscosity , γ w is unit weight of water

a) Grain size: The coefficient of permeability includes D102, where D10 is a measure of grain size

If the void ratio is the same then permeability is more in coarse soil than in the fine soil

b) Void ratio: From the equation, it is clear that k ∝ e2

If the particle size is the same, then loose soils are more permeable than dense soils

c) Degree of saturation: Permeability is directly proportional to the degree of saturation

d) Particle shape:

It is expressed in terms of specific surface area and permeability relates to specific surface area as ‘k ∝ 1/S2 ‘

e) Adsorbed Water

Adsorbed water is the water layer formed around the soil particle especially in the case of fine-grained soils. This reduces the size of the void space by about 10%. Hence, permeability reduces.