Soils are often subjected to uniform loading over large areas, such as from wide foundations, fills or embankments. Under such conditions, the soil which is remote from the edges of the loaded area undergoes vertical strain, but no horizontal strain. Thus, the settlement occurs only in one-dimension.

The compressibility of soils under one-dimensional compression can be described from the decrease in the volume of voids with the increase of effective stress. This relation of void ratio and effective stress can be depicted either as an arithmetic plot or a semi-log plot.

In the arithmetic plot as shown, as the soil compresses, for the same increase of effective stress Ds', the void ratio reduces by a smaller magnitude, from De₁ to De₂. This is on account of an increasingly denser packing of the soil particles as the pore water is forced out. In fine soils, a much longer time is required for the pore water to escape, as compared to coarse soils.

It can be said that the compressibility of a soil decreases as the effective stress increases. This can be represented by the slope of the void ratio – effective stress relation, which is called the coefficient of compressibility, a_v.

For a small range of effective stress,
The -ve sign is introduced to make a_v a positive parameter.

If e₀ is the initial void ratio of the consolidating layer, another useful parameter is the coefficient of volume compressibility, m_v, which is expressed as

It represents the compression of the soil, per unit original thickness, due to a unit increase of pressure.