A soil with a porosity of 50% would be classified as which USCS symbol?

A soil with a porosity of 50% would be classified as which USCS symbol?

• A. CH
• B. ML
• C. CL
• D. SM

Answer: (C)

A key idea here is that USCS classification uses grain size (clay vs silt) together with Atterberg limits to describe plasticity, not porosity alone. A porosity around 50% suggests a fine-grained soil, more clay-like than coarse-grained. Among the fine-grained symbols, a clay with relatively low plasticity is designated CL, while CH would indicate high plasticity clay (higher liquid limit and plasticity index). Silts would be labeled ML or SM depending on their texture. So a soil with 50% porosity that behaves like a low-plasticity clay fits best with the symbol CL.

A key idea here is that USCS classification uses grain size (clay vs silt) together with Atterberg limits to describe plasticity, not porosity alone. A porosity around 50% suggests a fine-grained soil, more clay-like than coarse-grained. Among the fine-grained symbols, a clay with relatively low plasticity is designated CL, while CH would indicate high plasticity clay (higher liquid limit and plasticity index). Silts would be labeled ML or SM depending on their texture. So a soil with 50% porosity that behaves like a low-plasticity clay fits best with the symbol CL.