What is the term for the distribution of different size groups within a soil sample?

The term that denotes the distribution of different size groups within a soil sample is "gradation." Gradation refers specifically to the range of particle sizes present in a soil sample and the way these particles are distributed. Understanding gradation is important because it influences the soil's physical properties, such as its permeability, compaction, and drainage capabilities.

Granulation typically refers to the process of forming granules, which is more about the behavior of soil particles rather than their size distribution. Texture describes the specific composition of the soil, such as the percentages of sand, silt, and clay, without necessarily focusing on the distribution among those sizes. Lastly, soil structure pertains to how soil particles aggregate and arrange into larger units, which does not directly relate to the size distribution of individual particles. Therefore, gradation is the most accurate term for describing the distribution of different size groups within a soil sample.