What classifies soils that have less than 50% passing the No. 200 sieve?

Soils classified as coarse-grained are those in which less than 50% of the material passes through a No. 200 sieve. This sieve size is significant as it separates finer particles from coarser ones. In coarse-grained soils, the presence of larger particles such as sand and gravel is predominant, leading to distinct physical characteristics like higher permeability and lower plasticity compared to finer soils.

The classification is important in engineering and construction, as coarse-grained soils generally offer better drainage and are less prone to issues associated with shrink-swell behavior, which is common in finer soils. This classification helps engineers determine the appropriate applications for such soils in various construction projects. Understanding the grain size distribution is crucial for effective soil management in civil engineering.

In contrast, fine-grained soils, such as those that would fall into the categories of clayey or organic, predominantly have more than 50% passing through the No. 200 sieve and exhibit different properties related to water retention, compaction, and plasticity.