Grain Size Distribution - Geotechnical Properties of Soil

In any soil mass, the sizes of the grains vary greatly. To classify a soil properly, you must
know its grain-size distribution. The grain-size distribution of coarse-grained soil is generally
determined by means of sieve analysis. For a fine-grained soil, the grain-size distribution
can be obtained by means of hydrometer analysis. The fundamental features of
these analyses are presented in this section. For detailed descriptions, see any soil mechanics
laboratory manual (e.g., Das, 2009).
Sieve Analysis
A sieve analysis is conducted by taking a measured amount of dry, well-pulverized soil and
passing it through a stack of progressively finer sieves with a pan at the bottom. The
amount of soil retained on each sieve is measured, and the cumulative percentage of soil
passing through each is determined. This percentage is generally referred to as percent
finer. Table 1.1 contains a list of U.S. sieve numbers and the corresponding size of their
openings. These sieves are commonly used for the analysis of soil for classification
purposes.

the logarithmic scale and the percent finer is plotted on the arithmetic scale.
Two parameters can be determined from the grain-size distribution curves of coarsegrained
soils: (1) the uniformity coefficient (Cu) and (2) the coefficient of gradation, or
coefficient of curvature (Cc).These coefficients are

Cu= D60/D10