High plasticity clay is classified as which type?

• A. Lean clay
• B. Fat clay
• C. Rich clay
• D. Dry clay

Answer: (B)

High plasticity clay is classified as fat clay. This classification is primarily based on the Atterberg limits, which are used to determine the plasticity and workability of soils. High plasticity clays exhibit a large plasticity index; they have a significant ability to deform without cracking or changing volume significantly.

Fat clays are characterized by their high clay content and moisture retention capability, which makes them very malleable and plastic. When subjected to loading or excavation, these clays can change shape significantly, which is important to consider in transportation engineering and structural applications. Understanding the properties of fat clays is crucial because they impact the stability and behavior of roads, foundations, and other civil structures.

Other classifications, such as lean clay, describe clays with lower plasticity characteristics that are stiffer and less deformable compared to fat clays. They typically have a smaller plasticity index and do not retain moisture as effectively. Rich clay refers to compositional properties rather than the plasticity status, and dry clay is a term that lacks specificity regarding plasticity in engineering terms. Thus, the designation of fat clay for high plasticity clay highlights its unique characteristics that are important for civil engineering applications.