Classification of Soil- Sieve Analysis

1. Introduction: As we know the soil is constituted of the three main phases, the solid phase, liquid phase, and the Air phase. The properties of the soil depends on some properties of these constituents and the composition of these three.

2. Index properties: There are some properties of the soil which are not of much importance for the Engineers but the knowledge of these properties can tell us about the Engineering properties like permeability, shear strength and earth pressure etc. These properties are known as the Index properties of the soil. Now according to these index properties we can classify the soil into different classes. The important index properties of the soil is the size and shape of the particles, Atterberg's limits, and the relative density.

1. Particle size and Shape: The soil particles can be of different diameter sizes, from 0.001mm to 300mm that of a clay to that of a cobble. The size of the particles affect its properties a lot. A fine grained soil is affected by the variation in the moisture content, but the coarse grained soil are not much affected by its moisture content. A fine grained soil become plastic when a moisture of some definite amount is put into it and it may also start to flow when the moisture content is increased to certain limit. Also the fine grained soil has the property of swelling and shrinking when we add or remove the moisture respectively. The permeability of the coarse grained soil is more as compared to fine grained soil because it compacts very less.
   The shape of the particles again affect the properties of the soil mass. The shape of the aggregates can be angular, sub-angular, sub-rounded, rounded, well rounded and flaky. The angular aggregates mass can have the e interlocking property so they can compact well to a denser mass. The rounded aggregates on the other hand have good strength but they have less, interlocking property. Rounded aggregates have a good workability too, but the flaky particles possess very less strength and also they have very less interlocking property too.

3.Soil Classification: The soil can be classified according to some index properties, and this classification becomes a mode of communication between the soil engineers. The classication of the soil into different groups having the similar properties, is known as the soil classification. From the above discussion one can assume that the fine grained soils behave in a similar way with the variation in the moisture content, so we can classify the soil according to their size.

1. Particle size classification of the Soil :
   The soil can be classified into various categories, as a fine grained soil or a coarse grained soil according to the size of the particles. There are various six froups created by the BIS:1498:1970, into which we can classify the soil according to the size of the present particles in it. Now to know the size of the particles, we can analyze the soil using the following techniques of the analysis:
   3.1.1. Mechanical Analysis(Sieve Analysis):
   In the mechanical analysis or the Sieve analysis, we take the soil sample and analyse it for its size with the help of the sets of the IS Sieve. The soil sample is divided into two sample by sieving it with the 4.36mm IS Sieve. It divides into coarse grained aggregates and another the fine sand. We can use the IS Sieves of the diameter, 80mm, 40mm, 20mm, 10mm, 4.36mm for the classification of the coarse grained soil. For the Fine grained soil we have to use the Sieve set of different sizes, 2mm, 1mm, 600mic, 425mic, 212mic, 150mic and 75mic.
   The sample is dried initially, and then it is put into the respective set of the IS Sieves, and it is shaked with the help of the sieve shaker. The particles of different sizes are retained on the different sieves according to their size. The sieves are shaken for a sufficient time and then the weight of the sample retained on the different IS Sieve is taken. The percentage of the weight retained on each sieve is calculated.