Particle-Size Analysis of Soils ASTM D422

Particle-Size Analysis of Soils ASTM D422

GRAIN SIZE ANALYSIS

SIEVE & HYDROMETER ANALYSIS

Purpose:

This test is performed to determine the percentage of different grain sizes

contained within a soil. The mechanical or sieve analysis is performed to

determine the distribution of the coarser, larger-sized particles, and the hydrometer

method is used to determine the distribution of the finer particles.

Standard Reference:

ASTM D 422 - Standard Test Method for Particle-Size Analysis of Soils

Significance:

The distribution of different grain sizes affects the engineering properties of

soil. Grain size analysis provides the grain size distribution, and it is required in

classifying the soil.

Equipment:

Balance, Set of sieves, Cleaning brush, Sieve shaker, Mixer (blender), 152H

Hydrometer, Sedimentation cylinder, Control cylinder, Thermometer, Beaker,

Timing device.

Test Procedure:

Sieve Analysis:

(1) Write down the weight of each sieve as well as the bottom pan to be used in the analysis.

(2) Record the weight of the given dry soil sample.

(3) Make sure that all the sieves are clean, and assemble them in the

ascending order of sieve numbers (#4 sieve at top and #200 sieve at

bottom). Place the pan below #200 sieve. Carefully pour the soil sample into the top sieve and place the cap over it.

(4) Place the sieve stack in the mechanical shaker and shake for 10

minutes.

(5) Remove the stack from the shaker and carefully weigh and record the

weight of each sieve with its retained soil. In addition, remember to

weigh and record the weight of the bottom pan with its retained fine soil.

Hydrometer Analysis:

(1) Take the fine soil from the bottom pan of the sieve set, place it into a

beaker, and add 125 mL of the dispersing agent (sodium hexametaphosphate (40 g/L)) solution. Stir the mixture until the soil is thoroughly wet. Let the soil soak for at least ten minutes.

(2) While the soil is soaking, add 125mL of dispersing agent into the

control cylinder and fill it with distilled water to the mark. Take the reading at the top of the meniscus formed by the hydrometer stem and

the control solution. A reading less than zero is recorded as a negative

(-) correction and a reading between zero and sixty is recorded as a

positive (+) correction. This reading is called the zero correction. The

meniscus correction is the difference between the top of the meniscus

and the level of the solution in the control jar (Usually about +1).

Shake the control cylinder in such a way that the contents are mixed

thoroughly. Insert the hydrometer and thermometer into the control

cylinder and note the zero correction and temperature respectively.

(3) Transfer the soil slurry into a mixer by adding more distilled water, if

necessary, until mixing cup is at least half full. Then mix the solution

for a period of two minutes.

(4) Immediately transfer the soil slurry into the empty sedimentation

cylinder. Add distilled water up to the mark.

(5) Cover the open end of the cylinder with a stopper and secure it with

the palm of your hand. Then turn the cylinder upside down and back

upright for a period of one minute. (The cylinder should be inverted

approximately 30 times during the minute.)

(6) Set the cylinder down and record the time. Remove the stopper from

the cylinder. After an elapsed time of one minute and forty seconds,

very slowly and carefully insert the hydrometer for the first reading.

(Note: It should take about ten seconds to insert or remove the

hydrometer to minimize any disturbance, and the release of the hydrometer should be made as close to the reading depth as possible

to avoid excessive bobbing).

(7) The reading is taken by observing the top of the meniscus formed by

the suspension and the hydrometer stem. The hydrometer is removed

slowly and placed back into the control cylinder. Very gently spin it in

control cylinder to remove any particles that may have adhered.

(8) Take hydrometer readings after elapsed time of 2 and 5, 8, 15, 30, 60

minutes and 24 hours

Data Analysis:

Sieve Analysis:

(1) Obtain the mass of soil retained on each sieve by subtracting the

weight of the empty sieve from the mass of the sieve + retained soil,

and record this mass as the weight retained on the data sheet. The

sum of these retained masses should be approximately equals the

initial mass of the soil sample. A loss of more than two percent is

unsatisfactory.

(2) Calculate the percent retained on each sieve by dividing the weight

retained on each sieve by the original sample mass.

(3) Calculate the percent passing (or percent finer) by starting with 100

percent and subtracting the percent retained on each sieve as a

cumulative procedure.

For example: Total mass = 500 g

Mass retained on No. 4 sieve = 9.7 g

Mass retained on No. 10 sieve = 39.5 g

For the No.4 sieve:

Quantity passing = Total mass - Mass retained

= 500 - 9.7 = 490.3 g

The percent retained is calculated as;

% retained = Mass retained/Total mass

= (9.7/500) X 100 = 1.9 %

From this, the % passing = 100 - 1.9 = 98.1 %

For the No. 10 sieve:

Quantity passing = Mass arriving - Mass retained

= 490.3 - 39.5 = 450.8 g

% Retained = (39.5/500) X 100 = 7.9 %

% Passing = 100 - 1.9 - 7.9 = 90.2 %

(Alternatively, use % passing = % Arriving - % Retained

For No. 10 sieve = 98.1 - 7.9 = 90.2 %)

(4) Make a semilogarithmic plot of grain size vs. percent finer.

(5) Compute Cc and Cu for the soil.

Hydrometer Analysis:

(1) Apply meniscus correction to the actual hydrometer reading.

(2) From Table 1, obtain the effective hydrometer depth L in cm (for

meniscus corrected reading).

(3) For known Gs of the soil (if not known, assume 2.65 for this lab

purpose), obtain the value of K.

(4) Calculate the equivalent particle diameter by using the following

formula:

D = K Square root L/t

Where t is in minutes, and D is given in mm.

(5) Determine the temperature correction CT from.

(6) Determine correction factor “a” from Table 4 using Gs.

(7) Calculate corrected hydrometer reading as follows:

Rc = RACTUAL - zero correction + CT

(8) Calculate percent finer as follows:

P = (Rc ×a)/ws ×100

Where WS is the weight of the soil sample in grams.

(9) Adjusted percent fines as follows:

PA = P * F200/100

F200 = % finer of #200 sieve as a percent

(10) Plot the grain size curve D versus the adjusted percent finer on the

semilogarithmic sheet.