CL clay class is described as which combination?

• A. Low porosity sand, high permeability
• B. Low plastic clay, high porosity but low permeability
• C. High plasticity clay with high permeability
• D. Gravelly sand with moderate permeability

Answer: (B)

In this soil-classification idea, the letters describe a soil’s grain makeup and plasticity behavior. CL means a clay with low plasticity: the “C” marks clay and the “L” signals low plasticity. Clays tend to have lots of tiny pore spaces (high porosity), but water moves through them very slowly because those pores are so small and tortuous, giving very low permeability. So a CL soil is best described as low plastic clay with relatively high porosity but low permeability. The other options don’t fit because they describe sands or clays with high plasticity, or combinations that aren’t characteristic of a clay with low plasticity.