Question

briefly explain the factors affecting permeability

Answer 1

The factors affecting the permeability of soil are as follows:

1. The shape and size of soil particle – The permeability of fine soil particle is less than the coarse soil particles. So we can say that the permeability of soil decreases as the soil particles become finer.
2. Void ratio – The permeability of soil increases with an increase in the void ratio. If the soil has more voids then the water will have more path to flow hence permeability increases with the increase in void ration
3. The degree of saturation – the permeability of soil increases with increase in the degree of saturation of the soil. If the soil is not fully saturated it will contain air in the voids which reduces the permeability of the soil. As the degree of saturation increases, the entrapped air reduces and the permeability of the soil increases. The permeability of partially saturated soil is much less than the permeability of fully saturated soil.
4. Soil structure – Soil structure is particularly important in the case of permeability clay. Fine grain soil with a flocculated structure has higher permeability than those having a dispersed soil structure. With the increase of moisture content in clayey soil the particles become more and more dispersed and so the permeability decreases with an increase in dispersion.
5. The viscosity of the following liquid (permeant) – The higher the viscosity of permeant lower is its permeability. Since with the rise in temperature, the viscosity of a fluid decreases so temperature also affects viscosity.
6. Effective stress – As the effective stress on a soil mass increases the void ratio decreases, therefore the permeability also decreases.