A curve which is plotted between the water content as abscissa and the corresponding dry density as ordinate is known as compaction curve.

Salient features of compaction curves are:

i) The curve is usually of a hyperbolic form when the points obtained from the tests are smoothly joined.

ii) The peak point of compaction curve is the point with the maximum dry density, corresponding to maximum dry density is water content is known as optimum water content.

iii) At water content lower the O.M.C. the soil is rather stiff and has lot of void spaces and therefore dry density is low.

iv) Water content beyond the O.M.C. reduces the dry density because the extra water start occupying the space which otherwise could have been occupied by soil grains under compaction.