SIMPLE DRY SIEVING

Dry sieving is the simplest of all methods of particle size analysis. According to the British Standard dry sieving may be carried out only on materials for which this procedure gives the same results as the wet seiving procedure. This means that is applicable only to clean gramiliar materials, which usually imples clean sandy or gravely soils that is, soils containing negligible amouns of particle of silt or clay sixe. If in doubt about the validity of the dry-sieving procedure should be followed instead.

If particles of medium gravel size or larger are present in significant amounts, the initial size of the sample required may be such that riffling is necessary at some stage to reduce the sample to a manageable size for fine sieving. The procedure is then referred to as “composite sieving”.

SAMPLE PREPARATION

The specimen to be used for the test is obtained from the original sample by riffling, or by subdivision using the cone-and-quarter method. The appropirate minimum quantity of material depends upon the maximum size of particles present, and is indicated in Table 1.

·         The specimen is placed on a tray is allowed to dry, preferably overnight, in an oven maintance at 105-110 ⁰C.

·         After drying to constant weight, the whole specimen is allowed to cool, and is weighted to an accuracy within 0,1 % or less of it is total mass.

Maximum size of material present in substantial proportion retained on BS sieve (mm).	Minimum mass of sample to be taken for seiving
Pass 2 mm or smaller	100 g
6,3	200 g
10	500 g
14	1 Kg
20	2 Kg
28	6 Kg
37,5	15 Kg
50	35 Kg
63	50 Kg
75	70 Kg
100	150 Kg
150	500 Kg
200	1000 Kg

Table 1 Minimum quantities for particle size test

EXECUITION OF THE TEST

Selection of sieves.

The complete range of sieves specified by the British Standard is given in table 2. It is not necessary to use all sieves for every test, but the sieves used should adequately cover the range of aperture size for each particular soil. For classification purpose we can use a shot set. The sieves to be used are selected to suit the size of sample and type of material.

Sieve frames must not be out of true, and should fit snugly one inside the other, to prevent escape of dust. Sieves are nested together with the largest aperture sieve at the top, and a receiving pan under the smallest aperture sieve at the bottom.

Construction	Aperture size full set	Standard set	Short set	Suitable sieve diameters
	A	B	C	450 mm	300 mm	200 mm
Preforated Steel Plated ( Square Holes)	75 mm 63 50 37,5 28 20 14 10 6,3 5	+ + + + + +	+ + +	+ + + + + +	+ + + + + + +
Woves Wire	3,35 2 1,18 600µm 425 300 212 150 63	+ + + + + + +	+ + + +	+ + +	+ + + +	+ + + + + + + + +
Lid and Receiver	+	+	+
	19 sieves	13 sieves	7 sieves

Table 2

Test Procedure

·         The dried soil sample is placed in the topmost sieve and is shaken long enough that all particles smaller than each aperture size can pass through. This can be achieved most conveniently by using a mechanical sieve shaker.

·         The shaker, he whole nest of sieves with receiving pan is placed in the dried soil is placed in the top sieve, which is then fitted with the lid, and the sieves are securely fastened down in the machine.

·         Agitation in the shaker should be for a minimum period of 10 min. Some shaker have a built-in timing device which can be pre-set to switch off the motor automatically after the desired period.

·         The maximum mass of sample, which can be sieved in one cycle, is depending on the used sieves and the particle size of the sample.

·         Weighting, the material retained on each sieve is tranferred to a container. Any particles lodged in the apertures of the sieve should be carefully removed with a sieve brush, the sieve being first placed upside-down an a tray or a clean sheet of paper. These particles are added to those retained on the sieve. Weighting of each size fraction should be to an accuracy of at least 0,1 % of the total initial test sample mass. The masses retained ( Ms^­­­­₁, Ms₂,--) are recorded.