A curve that is plotted between the water content as abscissa and the corresponding dry density as ordinate is the compaction curve.
The salient feature of compaction curves are:
- The curve is usually of a hyperbolic form when the points obtained from the tests are smoothly joined.
- The peak point of the compaction curve is the point with the maximum dry density, corresponding to maximum dry density is water content is known as optimum water content.
- At the water, content lower the O.M.C. the soil is rather stiff and has a lot of void spaces, and therefore dry density is low.
- Water content beyond the O.M.C. reduces the dry density because the extra water starts occupying the space which otherwise could have been occupied by soil grains under compaction.