Organic clays and silt clays are classified with which designation?

Organic clays and silt clays are classified with the designation "OH." This classification indicates that the soil contains a significant amount of organic matter, which can influence its physical and engineering properties. Organic soils, or soils with a high organic content, typically exhibit distinctive characteristics such as lower density and compressibility compared to inorganic soils. The "O" in the designation signifies that these soils have organic content, while the "H" denotes high plasticity. This classification is important in geotechnical engineering as it helps predict the behavior of the soil under different environmental and load conditions.

The other classifications represent different types of inorganic clays and silts, and do not pertain to organic content or the unique behavior associated with organic soils.