Sieve Analysis and Gradation Test
One stack of sieves tells you what a soil or aggregate actually is: how much of it is gravel, sand and fines, and whether the sizes work together or fight.
| Standards | ASTM C136 for aggregate, D6913 for soil |
| Fines boundary | 75 μm, the No. 200 sieve |
| Sand and gravel boundary | 4.75 mm, the No. 4 sieve |
| Key diameters from the curve | D10, D30 and D60, the sizes 10, 30 and 60 percent pass |
| Uniformity coefficient | Cu = D60 over D10 |
| Curvature coefficient | Cc = D30 squared over D60 times D10 |
| Well graded sand | Cu of 6 or more with Cc between 1 and 3 |
| Well graded gravel | Cu of 4 or more with Cc between 1 and 3 |
How the test works
Wash the sample over the 75 μm sieve first so the fines that cling to coarser particles actually leave, dry it, then shake it through the nested stack and weigh what each sieve retains. Convert to cumulative percent passing and plot against size on a log scale. The shape of that curve is the material: a steep curve is uniform, single sized stuff, a long gentle curve is well graded, and a flat step means a missing size range, the signature of a gap graded material.
Where it goes wrong
Skipping the wash is the classic flattering error: unwashed gradations always read cleaner than the truth, and the missing fines show up later as pumping subgrade or dirty concrete aggregate. Overloaded sieves blind and stop passing what should pass, so split big samples. And remember what the test cannot say: gradation counts particles, not behaviour. The moment meaningful material passes the 200, the fines need Atterberg limits before anyone claims to have classified the soil.
Related Calculators and Reference
- Grain Size Curve Plotter: plot the curve and read D10 to D60 automatically.
- Cu and Cc Calculator: the coefficients from your diameters.
- USCS Classification Tool: gradation plus limits into a group symbol.
- Hazen Permeability Calculator: what D10 says about drainage.
- Atterberg Limits Test: the other half of classification.
- Mesh to Micron Converter: turn a sieve number into its opening in microns.
- ASTM International: publisher of C136 and D6913.