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Consider the following statements:

1. Soil with high void ratio has always more coefficient of permeability than the soil with lower void ratio.

2. Constant head permeability test is used for fine grained soil.

3. As temperature increases, the coefficient of permeability of soil also increases.

4. As the specific surface area of soil particle increases, the coefficient of permeability decreases

Which of these statements are correct?


1. 1 and 2
2. 2 and 3
3. 1, 3 and 4 
4. 4 and 1

1 Answer

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Best answer
Correct Answer - Option 3 : 1, 3 and 4 

Explanation:

Permeability is defined as the property of a porous material that permits the passage or seepage of water (or other fluids) through its interconnecting voids.

Factors affecting the permeability of soil can be studied using the following equation.

\(K = \frac{1}{Z}\frac{{{e^3}}}{{1 + e}}\;\frac{{{\gamma _w}}}{\mu }\;\frac{1}{{{S^2}}}\)

Where, Z = constant; μ = dynamic viscosity of water;

S = specific surface;  γw = unit weight of water.

The factors affecting the permeability of soil can be summarised in the below-tabulated form:

Parameter

Description

Size of particle

Higher the size of particle higher will be the permeability

Specific surface area

Higher the specific surface area lower will be the permeability

Void Ratio

Higher the void ratio higher the permeability

Viscosity of water

Higher the viscosity lower will be the permeability and we know that the viscosity of liquids (water) increases with a decrease in temperature and hence, permeability reduces.

Degree of saturation

Higher the degree of saturation higher the permeability

Entrapped gases

Higher the amount of entrapped gasses in soil mass lower will be the permeability

Temperature:

  • As we know, with an increase in temperature viscosity of fluid decreases (Soil contains water inside its pores), so the overall viscosity of soil reduces. Further, the viscosity of soil is inversely proportional to its permeability from the above relation. Therefore, with a decrease in viscosity of soil, permeability increases.

 Tests for Permeability

  • In constant head permeameter, flow is allowed to take place from the medium under constant head in order to find the permeability of the medium.
  • This method is suitable for coarse-grained soil in which substantial discharge could be obtained from the given time because the permeability of coarse-grained soil is very high.
  • But in fine-grained soil, the time required to compute the discharge is high, so permeability comes out to be very less.

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