The factors affecting the permeability of soil are as
follows:
- 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.
- 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
- 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.
- 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.
- 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.
- Effective stress – As the effective stress on a soil mass
increases the void ratio decreases, therefore the permeability also
decreases.