Explain three phase system of soil.
As natural soil contains solid soil particles and water and air present in its voids such complex nature of soil sample is difficult to analyze its physical properties hence it is simplify and presented in its equivalent three phase diagram as shown in figure above. Depending upon three phase diagram of soil is classified in three categories. 1. Dry soil 2. Partially saturated soil 3. Fully saturated soil. However if we take a dry soil mass, the voids are filled with air only. In case of perfectly saturated soil the voids are filled completely with water. In case of partially saturated soil, both air and water are present in the voids.