Determine the percentage of different grain sizes contained within a soil (Particle Size Analysis)

Particle Size 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.

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.

Observation And Calculation

Total Weight of soil sample = 500

Group No.	Sieve No.	Dia (mm)	WT. Defined (gm)	%age Retained %	Commulative % age WT. Retained	% Passing
G R O U P No 1	4	4.75	30	6	6	94
	8	2.36	60	12	18	82
	10	2.00	28	5.6	23.6	76.4
	16	1.18	46	9.2	32.8	67.2
	30	0.6	44	8.8	41.6	58.4
	40	0.425	20	4	45.6	54.4
	50	0.3	64	12.8	58.4	41.6
	80	0.18	104	20.8	79.2	20.8
	100	0.15	0	0	79.2	20.8
	200	0.075	100	20	99.2	0.8
	Pan	0	0	0	0	0