The DCP is a practical test used for onsite measuring of road material strength.
The test provides an indication of a material’s in-situ resistance to penetration. Therefore, no samples need to be taken to a laboratory. It is often used to determine subgrade strength. The test is carried out by driving an approximately 2 metre steel rod with a metal cone tip with a 60 degree angle into the ground. It is repeatedly struck with an 8 kg (17.6 lb) weight, and making sure that the dropping distance is always 575 mm (2.26 feet). The penetration is measured after each blow and the results plotted. The slower the penetration into the soil, the stronger the penetration resistance of the material. This also indicates that the material will be able to withstand higher wheel and axle loads before penetration into the surface occurs. If the cone penetrates quickly into the soil, it indicates that the material has poor strength or insufficient compaction has been achieved. Either thicker pavement layers might be necessary or compaction needs to be improved.
The test results can be correlated with the California Bearing Ration (CBR – discussed in the January issue of Logging-on) by applying a formula. The cost of the test apparatus is relatively low (usually less than US$ 3,000 for hand-operated equipment) and the test only takes five to ten minutes to complete. However, it can save much time and money later by ensuring that the road is designed properly.
Source: http://pavementinteractive.org/index.php?title=Dynamic_cone_penetration_test