Question

What are the factors affecting coefficients of the permeability?

Answer 1

In order to answer this question, first we will discuss the coefficients of the permeability and then we will mention the factors that affect the coefficients of the permeability. And then we will discuss each mentioned factor separately.

Complete answer:
Under a unit hydraulic gradient, the coefficient of permeability is defined as the average velocity of flow over the total cross-sectional area of the soil mass. The letter $k$ stands for it. It has the same unit as velocities, such as $Cm.{\sec ^{ - 1}},{\text{ }}m.{\sec ^{ - 1}},{\text{ }}m.h{r^{ - 1}}$ , and so on.
The following are the factors that influence the coefficient of permeability:
(1) Size of particles:- The size of the soil particle affects permeability. Permeability is higher in coarse-grained soils, while it is lower in fine-grained soils.
(2) Shape of particles:- Particles with a rounded shape will have more permeability than those with an angular shape. It's because angular particles have a larger specific surface area than rounded particles.
(3) Void ratio:- Permeability rises with void ratio in general. However, it is not appropriate to all soil types. Clay, for example, has a higher vacancy ratio than any other form of soil, although it has a very low permeability. This is because, in the case of clays, the flow channel through voids is so narrow that water cannot easily pass through it.
(4) Degree of saturation:- Air gaps arise in partially wet soil due to entrapped air or gas released by the percolating fluid or water. This air will obstruct the flow channel, lowering permeability. Dirt that is fully saturated is more permeable than soil that is partially saturated.
(5) Water properties:- Permeability is also affected by other qualities of water or fluid, such as unit weight and viscosity. The unit weight of water, on the other hand, will have little effect because it does not change much with temperature.

Note: The permeability coefficient is proportional to water density and inversely proportional to its viscosity. The density of water does not change greatly as a function of temperature, but viscosity does.