Permeability of Soil

 

Permiability is the process of passage of water through the soil. Permeability is very high in coarse grain soil than the fine grain soil, because in fine grain soil, The soil particles are very closely  situated to each other hence, the water find it hard to pass through the soil.

The coefficient of permeability depends on the soil property, void ratio and temperature. The coefficient of permeability can be determined by conducting two tests in laboratory. These tests are i) Constant head permeability test and ii) variable head permeability test.

Constant head permeability test :

In this test a constant head of water is maintained .This test is done for coarse grain soil. The soil sample is placed between two porous stones . The soil is saturated completely before conducting the test. The coefficient of permeability is calculated by the following formula

K=QL/Aht

Where, Q= Discharge

L= Length of the specimen

A= cross section area of the  specimen

h= head causing flow

t= time

Variable head permeability test :

This test is performed for fine grain soils. In this test constant head of water is not maintained but instead two heads are measured at two different time.  In this test the coefficient of permeability is calculated by the given formula.

K= 2.303aL/At Log (h1/h2)