Particle size distribution curve (PSDC) is the semi log graph drawn as sieve size versus % finer of given soil sample. The PSDC is useful for grading of soil i.e. classification of soil based on its particle sizes available. Thus the outcome of sieve analysis is PSDC gives following types of soil as shown in figure above.
From above graph soil is classified based on grading curves as follows.
1. Fine grained soil: When line cuts Y-axis indicate more amount of fine particles.
2. Well graded soil: When PSDC is S-shaped indicates soil contains all particle sizes.
3. Uniformly graded soil: When line is almost vertical indicates particles of same sizes.
4. Coarse grained soil: When line cuts X-axis indicates more amount coarse particles available.
5. Gap graded soil: When graph is of wavy nature indicating particles of only specific size and deficiency of other sizes.