How to Determine Particle Size Distribution Of Soil

This test is done to determine the particle size distribution of soil as per IS: 2720 (Part 4) – 1985. The appratus required to do this test :-
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
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^oC. 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^oC.

Procedure to determine Particle Size Distribution Of Soil
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.

v) The material retained on 75µm IS Sieve is collected and dried in oven at a temperature of 105 to 120^oC for 24hrs. The dried soil sample is sieved through 2mm, 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 along with water are collected and put into a 1000ml 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

What About Hydraulic Jump

The abrupt increase in depth of rapidly flowing water is called hydraulic depth.Flow at the jump changes from a supercritical to a subcritical stage with an accompanying loss of kinetic energy. The change in depth occurs over a finite distance, known as the length of jump. The upstream surface of the jump, known as the roller, is a turbulent mass of water.

The depth before a jump is the initial depth, and the depth after a jump is the sequent depth. The specific energy for the sequent depth is less than that for the initial depth because of the energy dissipation within the jump.

F=[ d₂²- d₁²]w/2

where d₁ =depth before jump, ft (m)

d₂ =depth after jump, ft (m)

w=unit weight of water, lb/ft³ (kg/m³)

What is Sieve Analysis of Aggregates

SIEVE ANALYSIS
Sieve analysis helps to determine the particle size distribution of the coarse and fine aggregates.This is done by sieving the aggregates as per IS: 2386 (Part I) – 1963. In this we use different sieves as standardized by the IS code and then pass aggregates through them and thus collect different sized particles left over different sieves.

The apparatus used are -
i) A set of IS Sieves of sizes – 80mm, 63mm, 50mm, 40mm,31.5mm, 25mm, 20mm, 16mm, 12.5mm, 10mm, 6.3mm,4.75mm, 3.35mm, 2.36mm, 1.18mm, 600µm, 300µm, 150µm and 75µm.

ii) Balance or scale with an accuracy to measure 0.1 percent of the weight of the test sample.
The weight of sample available should not be less than the weight given below:-

The sample for sieving should be prepared from the larger sample either by quartering or by means of a sample divider.

Procedure to determine particle size distribution of Aggregates.
i) The test sample is dried to a constant weight at a temperature of 110 + 5^oC and weighed.
ii) The sample is sieved by using a set of IS Sieves.
iii) On completion of sieving, the material on each sieve is weighed.
iv) Cumulative weight passing through each sieve is calculated as a percentage of the total sample weight.
v) Fineness modulus is obtained by adding cumulative percentage of aggregates retained on each sieve and dividing the sum by 100.

Determining Water Content In Soil – Oven Drying Method

This test is done to determine the water content in soil by oven drying method as per IS: 2720 (Part II) – 1973. The water content (w) of a soil sample is equal to the mass of water divided by the mass of solids.
Apparatus required :-
i) Thermostatically controlled oven maintained at a temperature of 110 ± 5^oC
ii) Weighing balance, with an accuracy of 0.04% of the weight of the soil taken
iii) Air-tight container made of non-corrodible material with lid
iv) Tongs

PREPARATION OF SAMPLE
The soil specimen should be representative of the soil mass. The quantity of the specimen taken would depend upon the gradation and the maximum size of particles as under:

Procedure to determine Water Content In Soil By Oven Drying Method
i) Clean the container, dry it and weigh it with the lid (Weight ‘W₁‘).

ii) Take the required quantity of the wet soil specimen in the container and weigh it with the lid (Weight ‘W₂‘).

iii) Place the container, with its lid removed, in the oven till its weight becomes constant (Normally for 24hrs.).

iv) When the soil has dried, remove the container from the oven, using tongs.

v) Find the weight ‘W₃‘ of the container with the lid and the dry soil sample.

REPORTING OF RESULTS
The water content
w = [W₂-W₃] / [W₃ -W₁]*100%
An average of three determinations should be taken. A sample calculation is shown below

How to Determine The Plastic Limit Of Soil

This test is done to determine the plastic limit of soil as per IS: 2720 (Part 5) – 1985.The plastic limit of fine-grained soil is the water content of the soil below which it ceases to be plastic. It begins to crumble when rolled into threads of 3mm dia. The apparatus used:

i) Porcelain evaporating dish about 120mm dia.
ii) Spatula
iii) Container to determine moisture content
iv) Balance, with an accuracy of 0.01g
v) Oven
vi) Ground glass plate – 20cm x 15cm
vii) Rod – 3mm dia. and about 10cm long

PREPARATION OF SAMPLE
Take out 30g of air-dried soil from a thoroughly mixed sample of the soil passing through 425µm IS Sieve. Mix the soil with distilled water in an evaporating dish and leave the soil mass for naturing. This period may be upto 24hrs.

Procedure to determine The Plastic Limit Of Soil
i) Take about 8g of the soil and roll it with fingers on a glass plate. The rate of rolling should be between 80 to 90 strokes per minute to form a 3mm dia.

ii) If the dia. of the threads can be reduced to less than 3mm, without any cracks appearing, it means that the water content is more than its plastic limit. Knead the soil to reduce the water content and roll it into a thread again.

iii) Repeat the process of alternate rolling and kneading until the thread crumbles.

iv) Collect and keep the pieces of crumbled soil thread in the container used to determine the moisture content.

v) Repeat the process at least twice more with fresh samples of plastic soil each time.

REPORTING OF RESULTS
The plastic limit should be determined for at least three portions of the soil passing through 425µm IS Sieve. The average water content to the nearest whole number should be reported.

How to Determine The Specific Gravity Of Soil

This test is done to determine the specific gravity of fine-grained soil by density bottle method as per IS: 2720 (Part III/Sec 1) – 1980. Specific gravity is the ratio of the weight in air of a given volume
of a material at a standard temperature to the weight in air of an equal volume of distilled water at the same stated temperature.
The apparatus used:
i) Two density bottles of approximately 50ml capacity along with stoppers
ii) Constant temperature water bath (27.0 + 0.2^oC)
iii) Vacuum desiccator
iv) Oven, capable of maintaining a temperature of 105 to 110^oC
v) Weighing balance, with an accuracy of 0.001g
vi) Spatula

PREPARATION OF SAMPLE
The soil sample (50g) should if necessary be ground to pass through a 2mm IS Sieve. A 5 to 10g sub-sample should be obtained by riffling and oven-dried at a temperature of 105 to 110^oC.
Procedure to Determine the Specific Gravity of Fine-Grained Soil
i) The density bottle along with the stopper, should be dried at a temperature of 105 to 110^oC, cooled in the desiccator and weighed to the nearest 0.001g (W₁).
ii) The sub-sample, which had been oven-dried should be transferred to the density bottle directly from the desiccator in which it was cooled. The bottles and contents together with the stopper should be weighed to the nearest 0.001g (W₂).
iii) Cover the soil with air-free distilled water from the glass wash bottle and leave for a period of 2 to 3hrs. for soaking. Add water to fill the bottle to about half.
iv) Entrapped air can be removed by heating the density bottle on a water bath or a sand bath.
v) Keep the bottle without the stopper in a vacuum desiccator for about 1 to 2hrs. until there is no further loss of air.
vi) Gently stir the soil in the density bottle with a clean glass rod, carefully wash off the adhering particles from the rod with some drops of distilled water and see that no more soil particles are lost.
vii) Repeat the process till no more air bubbles are observed in the soil-water mixture.
viii) Observe the constant temperature in the bottle and record.
ix) Insert the stopper in the density bottle, wipe and weigh(W₃).
x) Now empty the bottle, clean thoroughly and fill the density bottle with distilled water at the same temperature. Insert the stopper in the bottle, wipe dry from the outside and weigh (W₄ ).
xi) Take at least two such observations for the same soil.

REPORTING OF RESULTS
The specific gravity G of the soil = (W₂ – W₁) / [(W₄-₁)-(W₃-W₂)]
The specific gravity should be calculated at a temperature of 27^oC and reported to the nearest 0.01. If the room temperature is different from 27^oC, the following correction should be done:-
G’ = kG
where,
G’ = Corrected specific gravity at 27^oC
k = [Relative density of water at room temperature]/ Relative density of water at 27^oC.
A sample proforma for the record of the test results is given below. Relative density of water at various temperatures is taken from table here.