Sieve Analysis - Soil Classification Gradation Curve
Sieve analysis is a procedure to assess the particle size distribution. Different sizes of sieves are used to classify the soil as uniformly graded, well graded, poorly graded or gap graded.
Sieve analysis is performed to assess the particle size distribution of granular material by allowing the fabric to undergo a series of sieves of progressively smaller mesh size and weighing the quantity of fabric that's stopped by each sieve as a fraction of the entire mass.
Boulders: grain size > 300 mm
Cobbler: grain size- 80 to 300 mm
Gravel: grain size- 4.75 to 80 mm
Coarse sand: grain size- 2 to 4.75 mm
Medium sand: grain size- 0.425 to 2 mm
Fine sand: grain size- 0.0075 to 0.425 mm
Silt: grain size- 2 micron to 75 micron
Clay: grain size < 2 micron
Boulders and Cobblers are not considered as soils. Silt and Clay are fine-grained soils. Sieve analysis is done by mechanical shaking (10-15 minutes) or manual shaking.
Cumulative percentage retained = sum of percentage retained on all the sieves of larger size and that of a particular size.
Percentage finer than the sieve under consideration = 100 - cumulative percentage retained.
Gradation from Sieve Analysis
The gradation is as follows
Well graded: All particle sizes are included
Uniformly graded: Most of the particles are of same size
Gap graded: Some of the particle sizes are missing
For the soils passing through 75 micron sedimentation analysis would be done, deflocculating agents are used to deflocculate the soil retained on 75 micron, then they may pass through 75 micron sieve.
Parameters - D10, D30 and D60
D60 = 60% particles are finer than the dia D60, similarly, D30 and D10 are also used.
D10 = Effective particle size
If all the soil particles are of D10 size then the soil will produce the same effect of original soil.
These parameters play an important role in soil characteristics like permeability, consistency limits and so on.