Clayey sands and poorly graded sand-clay mixes are categorized as which type?

Clayey sands and poorly graded sand-clay mixes fall into the category identified by the letters SC in the Unified Soil Classification System (USCS). The SC classification specifically refers to "Clayey Sands," which are characterized by their mixture of fine particles (clay) and coarse particles (sand).

This classification indicates that the material is primarily sandy in nature but has enough clay content to influence its engineering and physical properties significantly. The presence of clay contributes to increased plasticity and cohesion compared to clean sands, which can be essential when evaluating soil stability, drainage, and compaction behaviors in engineering applications.

In contrast, materials classified under other designations such as GC (Clayey Gravels), GM (Silty Gravels), or SM (Silty Sands) would exhibit different soil particle compositions or behaviors that do not apply to clayey sands or poorly graded sand-clay mixes. Thus, SC is the correct choice for identifying the type of soil in question.