Which major group of the Unified Soil Classification System includes coarse-grained soils?

• A. Fine-grained Soils
• B. Cohesive Soils
• C. Cohesionless Soils
• D. Organic Soils

Answer: (C)

The correct answer identifies coarse-grained soils within the Unified Soil Classification System (USCS). Coarse-grained soils, which primarily consist of particles larger than 0.075 mm, are categorized as cohesionless, meaning they do not exhibit significant cohesion or adhesive forces between particles. This group generally includes gravel and sand.

Cohesionless soils typically have high permeability and drainage characteristics, making them suitable for a variety of engineering applications. Understanding this classification is crucial for geotechnical engineers when assessing material properties for construction projects and predicting behaviors under stress and loading conditions.

Fine-grained soils contain smaller particles and typically include silts and clays, which possess cohesive properties. Cohesive soils are a subset of fine-grained soils characterized by their ability to retain water and support structural loads through cohesion. Organic soils consist of decomposed plant material and generally have differing mechanical properties that can complicate engineering applications.

Recognizing these distinctions helps in understanding the appropriate use and handling of the different soil types in practical engineering scenarios, particularly when surface drainage, stability, and strength are concerned.