Sieve Analysis and Sedimentation Analysis
The percentage of various size of particles in a dry soil sample is determined by particle size analysis or mechanical analysis. The mechanical analysis is carried out in two stages:
- Sieve analysis
- Sedimentation analysis or wet mechanical analysis
The sieve analysis is carried out for coarse-grained soil only, While sedimentation analysis is carried out for fine-grained soils.
Sieve analysis is carried out by using a set of stander sieves are designated by the size of the mesh in mm. Sieving is performed by arranging the various sieves one over the other in the order of their mesh openings.
The largest opening sieve is kept the top and the smallest opening sieve is kept the bottom. A receiver is kept at the bottom and a cover is kept at the top of the whole assembly.
The soil sample is put on the top sieve. Then shaking is given to the whole assembly for at least 10 minutes with the help of a shaking machine or by hand.
The portion of the soil sample retained on each sieve is weighed. The percentage of soil retained on each sieve is calculated. From these results, percentage passing through each sieve is calculated.
The results may be plotted on a semi-log graph paper with the percentage finer on the arithmetic scale and particle diameter on the log scale. A smooth curve can be drawn through them. This curve can indicate the type of soil.
Sedimentation analysis or wet mechanical analysis
Wet mechanical analysis is used for the analysis of soil finer than 75 microns in size. The analysis is based on Stoke’s law. The sedimentation analysis can be done either by a hydrometer or by a pipette. Both methods are based on the following assumption:
a) The particles are the perfect sphere.
b) The liquid through which the particles fall must be of indefinite extent.
c) The particle reaches constant terminal velocity within a few seconds and is maintained indefinitely.