Which soil property is most relevant for understanding elastic settlement?

Compressibility is the soil property most relevant for understanding elastic settlement because it directly relates to how much a soil volume decreases when stress is applied. Elastic settlement occurs when a load is applied to the ground, causing the soil to deform elastically and return to its original shape once the load is removed, provided the load is not sufficient to exceed the soil's yield point.

Soil compressibility is quantified by parameters such as the modulus of elasticity or the coefficient of volumetric compressibility. These parameters help engineers predict how much a soil will settle under a given load and are critical for designing foundations and other structures. A more compressible soil will experience greater elastic deformation for the same load compared to less compressible soils.

While the other properties like permeability, plasticity index, and granular size can influence various aspects of soil behavior, they do not directly measure the elastic deformation response to applied loads in the same way that compressibility does. Permeability relates to the soil's ability to drain water, plasticity index relates to the soil's behavior when wet or dry, and granular size impacts the soil's density and compaction but is less significant for understanding elastic settlement specifically.