17-01-2014, 03:01 PM
PARTICLE SIZE DISTRIBUTION
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 - 2mm, 600μm, 425μm,
212μm and 75μm
ii) A set of coarse IS Sieves of sizes - 20mm, 10mm and
4.75mm
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
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
o
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
o
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 2g of sodium hexametaphosphate or 1g of
sodium hydroxide and 1g of sodium carbonate per litre of
water, which is added as a dispersive agent. The soaking of
soil is continued for 10 to 12hrs.
ii) The sample is washed through 4.75mm IS Sieve with water
till substantially clean water comes out. Retained sample on
4.75mm IS Sieve should be oven-dried for 24hrs. This dried
sample is sieved through 20mm and 10mm IS Sieves.
iii) The portion passing through 4.75mm IS Sieve should be
oven-dried for 24hrs. This oven-dried material is riffled and
about 200g taken.
iv) This sample of about 200g is washed through 75μm IS Sieve
with half litre distilled water, till substantially clear water
comes 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 (see page 12 for sample chart).