Proctor compaction test

The Proctor compaction test is used to obtain the compressibility of soils and to determine the optimum moisture content at which the highest compaction can be achieved. The test is conducted for several different moisture contents. When loss of water occurs during compaction the maximum density is achieved. Furthermore, beyond a certain moisture content excess water within sample will result in an increase of pore water pressures, subsequently pushing the particles apart.
The results of all tests are subsequently plotted against water content and a Proctor-curve can be drawn to identify the maximum compaction and corresponding moisture content.

To verify the in-situ compaction, the bulk and dry density (and moisture content) of the soil in-situ is determined using a steel cutting ring (with known volume). The results are then compared to the achieved results of the Proctor test (at a 100% Proctor density), and used to assess the density of the compacted layer in-situ.