Ionuţ Vasiliniuc Almost as many particle size techniques that are out there (~ 300) have been used in the determination of soils and sediments' particle size. The most popular over the years have been screens/sieves and (for clays especially) sedimentation. In the last 15 to 25 years then light scattering methods (e.g. laser diffraction) have come to the fore. For an overview of popular methods and what the numbers mean see the attached. More on soils and sediments in general (including references and chapter pointers) in this webinar (free registration required):
Size and shape characterization in soils and sediments