The factors affecting permeability are given below.

1. Shape of particles
2. Void ratio of soil
3. Particle size
4. Structure of soil mass
5. Degree of saturation
6. Impurities in the water

7. Properties of water.

   1. Shape of particles: Angular particles have a greater specific surface area as compared to rounded particles the permeability is inversely proportional to the specific surface has for same word rescue that soil with angular particles is less permeable than those with the rounded particle.

   2. Void ratio of soil: The coefficient of permeability as $\frac{e_a}{(1+a)}$ . Thus the greater the void ratio higher is the coefficient of permeability.

   3. Particle size: The coefficient of permeability of soil is proportional to the square of the particle size. Thus, the permeability of coarse grained soil is more than that of fine grained soil.

   $K = CD_{10}^2$

   If $D_{10}$ is in mm and K is in $ms^{-1}$, the values of $C = \frac{1}{100}$.

   4. Structure of soil mass: For some void ratio the permeability is more for flocculant structure as compared to that in dispersed structure.

   5. Degree of saturation: The permeability of partially saturated soil is smaller than that of a fully saturated soil. Thus, this is due to the air pockets formed in the partially saturated soil

   6. Impurities in the water: The permeability may get reduced to the presence of foreign impurities in the water flowing through the soil mass.

   7. Properties of water: The coefficient of permeability is proportional to the Unit Weight of water $(\gamma_w)$ and inversely proportional to the viscosity $(\eta)$. There is no such variation in the unit weight but there is the large variation in viscosity $(\eta)$ with the variation in temperature. Thus the coefficient of permeability decreases with an increase in temperature due to the reduction in viscosity. The permeability (K) measured at temperature (T) in the laboratory can be corrected for standard temperature of 28 degree Celsius as followes:

   $K_{(28)} = \frac{k(\frac{\gamma_w}{\eta})_{28}}{(\frac{\gamma_w}{\eta})_{T}} \cong K. \frac{\eta_T}{\eta_{28}}$