Which soil types are classified as cohesionless?

• A. Clay and silt
• B. Sand and clay
• C. Gravel, sand, silt
• D. Clay and gravel

Answer: (C)

Cohesionless soils are defined by their inability to stick together due to a lack of cohesive forces, which are typically present in finer-grained soils like clay. The correct answer encompasses gravel, sand, and silt, as these soils primarily rely on friction rather than cohesion for their strength and stability.

Gravel and sand, being coarse-grained, have larger particle sizes that do not exhibit significant cohesion, allowing them to drain readily and create a free-draining environment. Silt, while finer and somewhat cohesive, can still be classified in this context as it does not adhere in the same manner as clay.

This grouping of gravel, sand, and silt highlights their similar characteristics, primarily their non-cohesive nature, which contrast sharply with clay, a cohesive soil type that binds particles together due to its plasticity and water retention capabilities. As a result, understanding the classifications of these soil types is crucial for applications in geotechnical engineering and construction, where soil behavior under load is a critical factor in design.