What does 'GM' represent in soil classification?

• A. Silty-gravels
• B. Clayey-gravels
• C. Clayey-sands
• D. Gravels

Answer: (A)

In soil classification, 'GM' stands for "Silty Gravels." This designation is part of the Unified Soil Classification System (USCS), which categorizes soils based on their grain size and plasticity. The 'G' in 'GM' indicates that the soil contains a significant proportion of gravel, while the 'M' denotes the presence of silt within that gravel matrix.

Understanding this classification is important for geotechnical engineers and soil scientists, as it informs decisions regarding the soil's engineering properties, drainage capabilities, and suitability for construction projects. Silty gravels are characterized by having a texture that is primarily composed of gravel-sized particles, with enough silt to influence their compaction and stability.

The other classifications like "Clayey-gravels," "Clayey-sands," and "Gravels" refer to different soil types that do not specifically include silt in their composition, which is why these options do not appropriately define 'GM' in the context of soil classification.