**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 (D**cm/s where

_{10})^{2}**D**= effective grain size of sand in cm.

_{10}Different relationships between void ratio and permeability, such as

**k µ**

**e**, and

^{3}/(1+e)**k µ e**. The value have been obtained from the Kozeny-Carman equation for laminar flow in saturated soil sample.

^{2}where **k _{o}** and

**k**are the key factors depending on the shape and tortuosity of the pores respectively also,

_{T}**S**is the outer surface area of the solid particles per unit volume of solid material, and

_{S}**g**and h are the unit weight and viscosity of the pore water content. The equation can be reduced to a simpler form as below

_{w}**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 **C _{k}** is the soil permeability change index and

**e**is a reference void ratio factor of soil.

_{k }