Table of Contents
Definition of sieve analysis
sieve analysis is the ratio of the mass of dry soil particles of the same sizes with a total mass of specimen in percentage measure by using the sieve of different standard sizes.
Introduction to sieve analysis of soil
Soils consist of particles with various sizes and shapes. sieve analysis is used to separate particles into size ranges and to determine quantitatively the mass of particles in each range. These data are combined to determine the particle-size distribution (gradation).
This test method uses a square opening sieve criterion in determining the gradation of soil between the 3 inches (75-mm) and No. 200 (75-m) sieves.
In cases where the gradation of particles larger than 3 inches (75 mm) sieve is required, Test Method ASTM D 5519 may be used.
In cases where the gradation of particles smaller than No. 200 (75-m) sieve is required, Test Method ASTM D 422 may be used.
Typically, if the maximum particle size is equal to or less than the 4.75 mm (No. 4 sieves), then single-set sieving is applicable.
Furthermore, if the maximum particle size is greater than the 4.75 mm (No. 4 sieves) and equal to or less than the 9.5 mm (3/ 8″ sieve), then either single-set sieving or composite sieving is applicable.
Finally, if the maximum particle size is equal to or greater than 19.0 mm (3/4 inch sieve), composite sieving is applicable. Sieving is carried out with wet or dry materials and the sieves are usually shacked manually or automatically.
Manual sieving: Suitable for coarser particles greater than 0.038 mm (No.400 sieve). Sieves are used one by one starting from the largest size.
Automatic sieving: Most often Practised for particle sizes ranged between 6.3 mm (1/4 inch) to 0.038mm (No.400 sieve). A standard series of 6 sieves are put together and shacked on a Ro-Tap automatic sieve shaker device for 5 to 20 minutes.
Dry sieving: Suitable for non-sticky and non-clay samples.
Wet sieving: Practised for finer size particles containing clay that have hard nature for dry screening.
Methods of sieve analysis
There are three (3) methods of sieve analysis
1. sieve analysis of soil by dry method
- Take a representative sample about 500 gm of soil, when soil contain larger particles (gravels), bigger soil sample will be required.
- If soil particles are lumped or conglomerated crush the lumped and not the particles using the pestle and mortar.
- Determine the mass of the sample accurately.
- Carefully check all the sieves and remove any particles sticking to the sieve mesh.
- Sieves are arranged in the descending order of their sizes with a pan at the bottom.
2.sieve analysis of soil by wet method
In case silt and clay particles are present in considerable amount in the soil sample the analysis of the soil may be done by wet sieving method more
3.sieve analysis of aggregate or gradation of fine and coarse aggregates
This test method is used to determine the grading of materials proposed for use as aggregates. The results are compared with applicable specification requirements and provide necessary data for control of the production of various aggregate products and mixtures containing aggregates. The gradation data may be used to calculate relationships between various aggregate or aggregate blends, to check compliance with such blends, and to predict trends during production by plotting gradation curves graphically.
Precaution of sieve analysis
- Sieve should be clean with a fine brush before and after use, should not be scrap with anything else.
- Sieves should be arranged in a proper manner i.e smaller (finer) sieve at the bottom and larger (coarser) sieve at the top.
- Sieve must be free of dust before use.
- after shaking, remove the sieves immediately.
Importance of sieve analysis
we can classify the soil into groups on the basis of results of the sieve analysis test and plastic index.
if passing % is wrong then the material group will be automatically wrong because we classify the material on the basis of sieve analysis.
if sieve analysis is wrong then liquid limit and plastic limit will also go wrong.
Gradation curve of sieve analysis
The gradation curve is obtained by plotting percentage passing on the y-axis and log of sieve sizes on the x-axis using a semi-log paper. Gradation curves are the best representation of soil nature i.e well-graded, uniformly graded or poorly graded soil.
Uniformity coefficient (Cu) and Coefficient of curvature (Cc) can also give us an idea of soil nature. They are calculated as follows:
Cc= (D30)2/ (D10)x(D60)
Where,D10, D30, or D60 are diameters for 10%, 30% and 60% passing respectively.
COEFFICIENT OF UNIFORMITY AND CURVATURE
A coefficient related to the size distribution of granular material, obtained by dividing the size of the sieve (in mm) of which 60% of the sample weight passes by the size (in mm) of the sieve of which 10% of the sample weight passes.
The coefficient of uniformity, Cu is a crude shape parameter and is calculated using the following equation:
Cu=D60/D10 Where D60 is the grain diameter at 60% passing, and D10 is the grain diameter at 10% passing.
The coefficient of curvature, Cc is a shape parameter and is calculated using the following equation:
Cc= (D30)2/ (D10)x(D60)
Where D60 is the grain diameter at 60% passing, D30 is the grain diameter at 30% passing, and D10 is the grain diameter at 10% passing. Calculate the coefficients of uniformity and curvature grain diameters in millimeters is required. Grain diameter is calculated from a known distance and time of the fall of the particle. This is used to classify fine-grained soils. This means that if 40% of the sample is retained on the No. 20 sieve then there is 60%
passing the No. 20 sieve.
Gradation of a soil can also be determined by calculating the coefficient of uniformity, Cu, and the coefficient of curvature, Cc, of the soil and comparing the calculated values with published gradation limits.