Factors affecting Permeability of soil
In case of soil mass , the permeant or pore fluid content is mostly water content whose variation in properties is generally very less amount. Permeability of all type of soil mass is strongly effected by the density of packing of the entire soil particles and molecules, which can also be represented by void ratio (e) or porosity (n) factor.
For Sand sample
In case sand, permeability can be empirically fully related to the square of some representative soil grain size from its grain-size distribution analysis. For filter of sand of any type, Allen Hazen in 1911 found that k » 100 (D10)2 cm/s where D10= effective grain size of sand in cm.
Different relationships between void ratio and permeability, such as k µ e3/(1+e), and k µ e2. The value have been obtained from the Kozeny-Carman equation for laminar flow in saturated soil sample.
where ko and kT are the key factors depending on the shape and tortuosity of the pores respectively also, SS is the outer surface area of the solid particles per unit volume of solid material, and gw and h are the unit weight and viscosity of the pore water content. The equation can be reduced to a simpler form as below
For Silt and Clay type soil
For silts and clay , the Kozeny-Carman equation does not work well condition , and log k versus e plot graph has been found to indicate a linear relationship.
For clayey soil particle, it is typically found that ,
where Ck is the soil permeability change index and ek is a reference void ratio factor of soil.