What are the commonly used soil classification systems based on grain size?

The choice of the Unified Soil Classification System and AASHTO as commonly used soil classification systems is accurately aligned with the standards in the field of soil engineering and geotechnical engineering.

The Unified Soil Classification System (USCS) is widely used to categorize soils based on their physical and engineering properties. It is essential for understanding how different soil types behave under various conditions, especially when it comes to construction and building foundations. The USCS classifies soils into groups based on grain size, consistency, and plasticity, making it a practical tool for engineers and contractors.

AASHTO, which stands for the American Association of State Highway and Transportation Officials, provides another classification system often utilized for highway and road construction applications. This system is particularly valuable in characterizing soils based on their suitability for construction and subgrade performance.

Both systems focus on grain size and other physical properties, enabling professionals to determine the appropriate practices for soil management, construction methods, and design frameworks, which highlights their importance in the industry.

The other choices involve systems like Soil Taxonomy, which is primarily used for agricultural and ecological studies, and ASTM, which involves various standards but doesn't specifically focus on grain size classification like the Unified Soil Classification System and AASHTO do