TO DETERMINE THE PARTICLE SIZE DISTRIBUTION OF A SOIL BY SEIVING

Theory:

The soil is sieved through a set of sieves. The material retained on different sieves is determined. The percentage of material retained on any sieve is given by

clip_image001

Where clip_image002= mass of soil retained on sieve ‘n’

M= total mass of the sample.

The cumulative percentage of the material retained

clip_image003

Whereclip_image004, clip_image005 etc are the percentages retained on sieve 1, 2 etc which are coarser than sieve ‘n’. The percentage finer than the sieve ‘n’

clip_image006

Equipment:

1. Set of fine sieves, 2mm, 1mm, 600micron, 425, 212, 150, and 75 micron.

2. Set of coarse sieves, 100mm, 80mm, 40mm, 10mm, and 4.75mm.

3. Weighing balance with accuracy of 0.1% of the mass of the sample.

4. Oven

5. Mechanical shaker

6. Trays

7. Mortar with a rubber covered pestle.

8. Brushes

9. Riffler

Part-I: Coarse Sieve Analysis

Procedure:

1. Take the required quantity of the sample. Sieve it through a 4.75mm Is sieve. Take the soil fraction retained on 4.75mm IS sieve for the coarse sieve analysis (Part-I) and that passing through the sieve for the fine sieve analysis (Part-II).

2. Sieve the sample through the set of coarse sieves by hand. While sieving through each sieve, the sieve should be agitated such that the sample rolls in irregular motion over the sieve, the material retained on the sieve may be rubbed with the rubber pestle in the mortar, if necessary. Care shall be taken so as not to break the individual particles. The quantity of the material taken for sieving on each sieve shall be such that the maximum mass of material retained on each sieve does not exceed the specified value.

3. Determine the mass of the material retained on each sieve.

4. Calculate the percentage of soil retained on each sieve on the basis of the total mass of the sample, taken in step (1).

5. Determine the percentage passing through each sieve.

Part-II: Fine Sieve Analysis.

6. Take the portion of the soil passing 4.75 mm IS sieve. Oven dry it at 105 to 1100C. Weigh it to 0.1% of the total mass.

7. Sieve the soil trough the nest of fine sieves, the sieves should be agitated so that the sample rolls in irregular motion over the sieves. However, no particles should be pushed through the sieve.

8. Take the material retained on various sieves in a mortar. Rub it with rubble pestle, but do not try to break individual particles.

9. Reserve the material through the nest of sieves. A minimum of 10min of shaking is required if a mechanical shaker is used.

10. Collect the soil fraction retained on each sieve in a separate container. Take the mass.

11. Determine the percentage retained, cumulative percentage retained, and the percentage finer, based on the total mass taken in step (1).

Data Sheet for Sieve Analysis

Total mass of dry soil=­­­­­­­­­­______g

Mass of soil retained on 4.75mm sieve = ________g

Mass of soil passing 4.75mm sieve = _______g

 

S.No.

OBSERVATIONS

CALCULATIONS

IS Sieve

Size of opening

Mass of soil retained

Percentage retained

Cumulative % retained

% finer

 

Coarse Fraction (Part-I)

 

100 m

100 mm

 

 

 

 

 

80 mm

80 mm

 

 

 

 

 

40 mm

40 mm

 

 

 

 

 

20 mm

20 mm

 

 

 

 

 

10 mm

10 mm

 

 

 

 

 

4.75 mm

4.75 mm

 

 

 

 

 

Fine Fraction (Part-II)

 

2 mm

2 mm

 

 

 

 

 

1 mm

1 mm

 

 

 

 

6

600 clip_image001

0.600 mm

 

 

 

 

 

425 clip_image001

0.425 mm

 

 

 

 

 

300 clip_image001

0.300 mm

 

 

 

 

 

212 clip_image001

0.212 mm

 

 

 

 

 

150 clip_image001

0.150 mm

 

 

 

 

 

75 clip_image001

0.075 mm

 

 

 

 

 

clip_image002

-         

 

 

 

 

 

 

Result:

Percentage finer given in the last column can be used to plot the particle size distribution curve with particle size as abscissa on log scale and the percentage finer as ordinate.

Particle size distribution on semi log graph

Fig: Particle size distribution on semi log graph

 

Grading of soils

Fig: Grading of soils

[Note: If the fraction contains an appreciable amount of clay particles, the wet sieve analysis is required. Alternatively following method may be used.

Before conducting step (7), add the water containing sodium hexa-mataphosphate at the rate of 2g per litre of water to the soil fraction. Stir the mix thoroughly and leave for soaking. Wash the soaked specimen on a 75clip_image003[4] IS sieve until the water passing the sieve is clear. Take the fraction retained on the sieve and dry it in an oven. Sieve the oven dried soil through the nest of sieves as discussed in step (7). Perform further steps as before.

Obviously the mass of material which would have been retained on pan is equal to the original mass of the soil before washing minus the dry mass of the soil retained on 75clip_image003[5]sieve after washing.]