Sieve analysis of soil

 

 

Sieve analysis of coarse and fine grained soil                           

Objective and Scope: The objective of the experiment to determine the grain size distribution of coarse grain soil by sieving.

Material and equipment

·         Balance accurate to 1gm

·         Set of is sieves

·         Thermostatically controlled oven

·         Water tight trays

·         Mechanical sieve shaker

·         Riffler

Theory:

In order to classify a soil for engineering purpose, one needs to knows the distributions of the size of grains in soil sample. Sieve analysis is a method to determine the grain size distribution of soils. Sieves are made of woven wires with square openings.

The soil is sieved through the set of sieve. The material is retained on the different sieve is determined. The percentage of material retained in sieve is given by

                                  

Where, M_n=Mass of soil retained on sieve “

           M=Total Mass of soil sample 

 

The results of the mechanical analysis are plotted to get a particle size distribution curve with the percentage finer N as the ordinate and the particle diameter as the abscissa, the dia1neter being plotted on a logarithmic scale. Figure shows some typical curves for various soils. A particle size distribution curve gives us an idea about the type and gradation of the soil. A curve situated higher up or to the left represents a relatively fine grained soil while a curve situated to the right represents a coarse grained soil.

A soil sample may be either well graded or poorly graded (uniformly graded). A soil is said to be well graded when it has good representation of particles of all sizes. On the other hand, a soil is said to be poorly graded if it has an excess of certain particles and deficiency of other, or if it has 1nost of the particles of about the sa1ne size; in the latter case it is known as a uniformly graded soil. Thus, soil A (Fig) is well graded while soil B is uniformly graded. A curve with a flat portion represents a soil in which some intermediate size particles are 1nissing (soil E in Fig.). Such a soil is known as gap graded or skip graded.

For coarse grained soil, certain particle sizes such as D₁₀ D₃₀ and D₆₀ are important. The D₁₀ represents a size, in mm such that 10% of the particle les are finer than this size. Similarly, the soil particle less finer than D₆₀ size are 60 per cent of the total mass of the sample. The size D 10 is sometimes called the effective size or effective diameter. The unifbm1ity coefficient Cu (or coefficient of uniformity) is a measure of particle size range and is given by the ratio of D₆₀ and D₁₀ sizes:

                                   

 

Similarly the shape of particles size curve is represented by the coefficient of curvature is given by ,

 

                       

 

For uniformly graded soil C_U is equal to unity. For a well graded soil C_C must be equal to 1to 3 in additional C_U must be greater than 4 for gravel and 6 for sands (USBR1960)

Procedure:

For coarse sieve analysis

·        Take the required quantity of sample. Sieve it through a 4.75mm IS sieve. Take the soil fraction retained on 4.75mm IS sieve for the coarse sieve analysis and that passing through the sieve for the fine sieve analysis.

·        Sieve the sample through the set of coarse sieve in mechanical sieve.

·        Determine the mass of the materials retained in each sieve.

·        Calculate the percentage retained through each sieve on the basis of total mass of the sample taken.

·        Determine the percentage passing through each sieve.

For Fine sieve analysis

·        Take the portion of the soil sample passing 4.75mm IS sieve. Oven dry it at 105 to 110⁰C. weight it to 0.1% of the soil mass.

·        Sieve the sample through the set of coarse sieve in mechanical sieve.

·        Take the material retained on various sieves in a mortar. Rub it with rubber pestle, but do not try to break individual particles.

·        Revise the materials through the nest of sieve.(minimum 1o minute od shaking)

·        Collect the soil fraction retained on each sieve in a separate container. Take the mass

·        Determine the percentage retained, cumulative percentage retained and percentage finer based on the total mass of sample taken.

Observation and calculations:

Total mass of Dry soil= 400gm

Mass of soil retained on 4.75mm sieve= 200gm

Mass of soil passing through 4.75mm sieve= 200gm

S.N
	IS sieve(mm)	Mass of soil retained (gm)	Percentage retained (%)	Cumulative % retained	% finer
Coarse fraction
1	100	-
2	80	-
3	40	-
4	20	30gm	7.50	7.50	92.50
5	10	62gm	15.50	23.00	77.00
6	4.75	108gm	27	50.00	50.00
Fine fraction
7	2	30.5gm	7.62	57.62	42.38
8	1	24.0gm	6.0	63.62	36.38
9	600µ	17.5gm	4.38	68.00	32.00
10	425µ	16.0gm	4.0	72.00	28.00
11	300µ	14.0gm	3.50	75.50	24.50
12	212µ	18.0gm	4.50	80.00	20.00
13	125µ	22.0gm	5.50	85.50	14.50
14	75µ	36.0gm	9.0	94.50	5.50
15	Pan	22.0gm	5.50	100.00

 

 

 

Result:

Percentage finer given in the last column can be used to plot the particle size distribution curve with particle size as abscissa on log scale and the percentage finer and ordinate. [Note. If the fine fraction contains as appreciable amount of clay particles, the wet sieve analysis is required]

Conclusion

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