GRAIN SIZE ANALYSIS
(Detailed Procedure given in IS 2720 (Part-IV)
(a). Select sieves as per I.S. specifications and perform sieving.
(b). Obtain percentage of soil retained on each sieve.
(c). Draw graph between log grain size of soil and % finer/passing.
NEED AND SCOPE OF EXPERIMENT
The grain size analysis is widely used in classification of soils. The data obtained from grain size distribution curves is used in the design of filters for earth dams and to determine suitability of soil for road construction, air field etc. Information obtained from grain size analysis can be used to predict soil water movement although permeability tests are more generally used.
3.Rubber pestle and mortar.
4.mechanical Sieve Shaker
The grain size analysis is an attempt to determine the relative proportions of different grain sizes which make up a given soil mass.
Soil passing 4.75mm I.S. Sieve and retained on 75micron I.S. Sieve contains no fines.
Take 500gm of the soil sample after taking representative sample by quartering.
I.S sieves are selected and arranged in the order as shown in the data sheet.
The sieving may be done either by hand or by mechanical sieve shaker for 10 minutes.
The weight the material retained on each sieve is recorded.
The percentage retained on each sieve is calculated on the basis of the total weight of the soil sample taken.
From these results the percentage passing through each of the sieves is calculated.
The moisture content of soil if above 5% it is to be measured and recorded.
Note: No particle of soil sample shall be pushed through the sieves.
Draw graph between log sieve size vs % finer/passing. The graph is known as grading curve. Corresponding to 10%, 30% and 60% finer, obtain diameters from graph are designated as D10, D30, D60.
Grain size analysis of soils by hydrometer analysis test.
To determine the grain size distribution of soil sample containing appreciable amount of fines.
To draw a grain size distribution curve.
For determining the grain size distribution of soil sample, usually mechanical analysis (sieve analysis) is carried out in which the finer sieve used is 75 micron or the nearer opening. If a soil contains appreciable quantities of fine fractions in (less than 75 micron) wet analysis is done. One form of the analysis is hydrometer analysis. It is very much helpful to classify the soil as per ISI classification. The properties of the soil are very much influenced by the amount of clay and other fractions.
Take 40gm of the oven dry soil sample after removing soluble salts and organic matter if any.
Mix the soil sample with 4% solution of dispersing agent in water (Sodium hexametaphosphate solution) to get a known amount of suspension by volume and stirred well. This suspension should be made 24 hrs before testing.
In the measuring cylinder the suspension is turned end to end for even distribution of particles before the time ‘t’ begins to be measured.
The hydrometer readings are recorded at regular intervals as indicated in the data sheet.
From the data obtained the particle size distribution curve is plotted in the semi-logarithmic graph sheet.
Composite Correction for Dispersion Agent and Temperature, (Ct – Cd):
Insert the hydrometer in the comparison cylinder containing dispersant solution in distilled water with the same concentration as used for making the soil suspension. The Composite correction (Ct – Cd) is negative of the hydrometer reading corresponding to the top meniscus.
For Sieve Analysis [PDF 119kB]
For Hydrometer Analysis [PDF 138kB]
GSD Log Plot [PDF 43kB]