What is the classification for clayey gravels and poorly graded gravel-and-clay mixes?

The classification for clayey gravels and poorly graded gravel-and-clay mixes falls under the group symbol "GC" in the Unified Soil Classification System (USCS). This designation indicates that the material is primarily gravel but contains a significant amount of clay, which influences its physical properties and behavior.

Clayey gravels (GC) are characterized by a granular skeleton made up of gravel-sized particles with a notable presence of clay fine particles. The presence of clay impacts the soil's cohesion and plasticity. This classification helps geotechnical engineers determine how the material will behave under various loading conditions and environmental changes, as well as its suitability for construction projects.

The other classifications do not accurately describe clayey gravels. For instance, "SM" represents silty sands, "SC" refers to clayey sands, and "ML" denotes low plasticity silts—none of which specifically capture the characteristics of gravel mixed with clay. Hence, GC is the appropriate classification for these types of soils due to its specific criteria relating to grain size and plasticity associated with clay content.