In soil classification, what is the composition of a material with 30% clay, 45% silt, 18% sand, and 7% gravel?

• A. Clayey silt, some sand, and gravel
• B. Clayey sand with some silt
• C. Sandy loam with trace gravel
• D. Gravelly clay with some silt

Answer: (A)

The classification of soil is based on its particle size distribution, which includes percentages of clay, silt, sand, and gravel. In this case, with a composition of 30% clay, 45% silt, 18% sand, and 7% gravel, the dominant component is silt, followed by clay, sand, and a minor portion of gravel.

The term "clayey silt" is appropriate here as the principal component is silt (45%), and clay (30%) is also present in significant quantity compared to sand and gravel. The inclusion of “some sand” acknowledges the 18% sand content, which, while not the dominant particle size, still contributes to the overall texture of the soil. The mention of gravel is accurate but emphasizes its minor role with only 7%.

This classification aligns with the Unified Soil Classification System (USCS), which emphasizes the dominant textures and provides a clear and accurate descriptive term based on the percentages of each type of soil particle present. Thus, identifying it as "clayey silt, some sand, and gravel" succinctly conveys the material's characteristics in a classification that is widely recognized in soil science.