PARTICLE SIZE DISTRIBUTION of Soil

Updated: Jul 16, 2020

AIM

To determine the particle size distribution of soil as per IS: 2720

(Part 4) - 1985.

APPARATUS

i) A set of fine IS Sieves of sizes - 2 mm, 600µm, 425µm,

212µm and 75µm

ii) A set of coarse IS Sieves of sizes - 20 mm, 10 mm and

4.75 mm

iii) Weighing balance, with an accuracy of 0.1% of the weight of

sample

iv) Oven

v) Mechanical shaker

vi) Mortar with rubber pestle

vii) Brushes

viii) Trays

PREPARATION OF SAMPLE

i) Soil sample, as received from the field, should be dried in air

or in the sun. In wet weather, the drying apparatus may be

used in which case the temperature of the sample should

not exceed 60 °C. The clod may be broken with wooden

mallet to hasten drying. Tree roots and pieces of bark

should be removed from the sample.

ii) The big clods may be broken with the help of wooden

mallet. Care should be taken not to break the individual soil

particles.

iii) A representative soil sample of required quantity as given

below is taken and dried in the oven at 105 to 120 °C.


PROCEDURE

i) The dried sample is taken in a tray, soaked in water and

mixed with either 2 g of sodium hexametaphosphate or 1 g of

sodium hydroxide and 1 g of sodium carbonate per litre of

water, which is added as a dispersive agent. The soaking of

soil is continued for 10 to 12 hrs.

ii) The sample is washed through 4.75 mm IS Sieve with water

till substantially clean water comes out. Retained sample on

4.75 mm IS Sieve should be oven-dried for 24 hrs. This dried

sample is sieved through 20 mm and 10 mm IS Sieves.

iii) The portion passing through 4.75 mm IS Sieve should be

oven-dried for 24 hrs. This oven-dried material is riffled and

about 200 g taken.

iv) This sample of about 200 g is washed through 75µm IS Sieve

with half litre distilled water, till substantially clear water

comes out.

v) The material retained on 75µm IS Sieve is collected and

dried in oven at a temperature of 105 to 120 °C for 24 hrs. The

dried soil sample is sieved through 2 mm, 600µm, 425µm

and 212µm IS Sieves. Soil retained on each sieve is

weighed.

vi) If the soil passing 75µm is 10% or more, hydrometer method

is used to analyse soil particle size.

HYDROMETER ANALYSIS

i) Particles passed through 75µm IS Sieve alongwith water are

collected and put into a 1000 ml jar for hydrometer analysis.

More water, if required, is added to make the soil water

suspension just 1000ml. The suspension in the jar is

vigorously shaken horizontally by keeping the jar in-between

the palms of the two hands. The jar is put on the table.

ii) A graduated hydrometer is carefully inserted into the

suspension with minimum disturbance.

iii) At different time intervals, the density of the suspension at

the centre of gravity of the hydrometer is noted by seeing

the depth of sinking of the stem. The temperature of the

suspension is noted for each recording of the hydrometer

reading.

iv) Hydrometer readings are taken at a time interval of

0.5 minute, 1.0 minute, 2.0 minutes, 4.0 minutes, 15.0

minutes, 45.0 minutes, 90.0 minutes, 3hrs., 6hrs., 24hrs.

and 48hrs.

v) By using the nomogram given in IS: 2720 (Part 4) - 1985,

the diameter of the particles for different hydrometer readings

is found out.

REPORTING OF RESULTS

After completing mechanical analysis and hydrometer analysis,

the results are plotted on a semi-log graph with particle size as

abscissa (log scale) and the percentage smaller than the

specified diameter as ordinate.

15 views0 comments

Recent Posts

See All