Factors affecting co-efficient of permeability of soil

Hello

There is an equation known as Poiseuille's equation, which when compared with the Darcy's law gives the value of coefficient of permeability,

  k = C.Yw/U * Ds^2 * e^3/ (1+e)

 In above equation, the factor k depends on:

(1) Grain Size: Allen Hazen found that the co-efficient of permeability can be expressed as 

                                k(in cm) = c.(D10)^2

  where, D10= effective diameter(cm)

              C = constant, approximately equal to 100.

(2) Properties of pore fluid: 

  viscosity of the fluid affects the flow, more the viscosity less is the fluidity so it is inversely proportional to the viscosity.

 k1/k2 = n2/n1

(3) Void ratio: 

Based on the mean hydraulic radius it can be written that,

k1/k2 = (e1/e2)^2

(4) Structural arrangements: Depending upon the method of compaction and condition existing during deposition, the structural arrangement of soil mass may vary at the same void ratio and consequently permeability also varies. it is defined by the factor C is the above equation.

For stratified deposits the flow is different for flow parallel and perpendicular or stratification.

(5) Degree of saturation and other foreign matter:

The permeability is affected by the partial saturation of the soil, when it has entrapped the air inside. Other foreign matter has the general tendency to flow towards the critical flow channel and thus choking it.

(6) Adsorbed water: The adsorbed water held on the surface of colloidal particles are highly cohesive and is immobile to normal hydrodynamic forces. Because of this the area of effective void space is reduced and thus permeability is reduced.

Thanks!