What type of soil is classified as having particle sizes smaller than 0.074 mm?

Soil that is classified as having particle sizes smaller than 0.074 mm is classified as clay. Clay particles are the finest among soil grades and exhibit unique properties due to their small size, which contributes to their plasticity and cohesion. This finer texture enables clay soils to retain water and nutrients more effectively than coarser soils, making them essential in many agricultural applications.

In this context, silt, while also fine, has particle sizes that range from 0.002 mm to 0.074 mm, which means it is not classified under the size of clay. Additionally, sand and gravel have much larger particle sizes and do not fall under the category of fine soils. Sand particles range from 0.074 mm to 2 mm, and gravel consists of larger particles typically above 2 mm. Understanding these classifications helps in identifying soil types for various applications in geotechnical engineering and hydraulic structures.