What is the purpose of a dynamic cone penetration test?
Dynamic cone penetration test (DCPT) is widely used for field quality assessment of soils. Its application to predict the engineering properties of soil is globally promoted by the fact that it is difficult to obtain undisturbed soil samples, especially when loose or submerged sandy soil is encountered.

The Dynamic Cone Penetration Test provides a measure of a material’s in-situ resistance to penetration. The test is performed by driving a metal cone into the ground by repeated striking it with a 17.6 lb (8 Kg) weight dropped from a distance of 2.26 feet (575 mm). The penetration of the cone is measured after each blow and is recorded to provide a continuous measure of shearing resistance up to 5 feet below the ground surface. Test results can be correlated to California Bearing Ratios, in-situ density, resilient modulus, and bearing capacity.

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What are the limitations of a dynamic cone penetrometer test?
​1.  Surcharge Loading – The strength of a subgrade material is dependent on the confining pressure and the associated surcharge loading of the pavement structure above. Typically, when the DCP testing is undertaken, all surcharge loading is removed (i.e. in a borehole or test pit) and may not ideally represent the in-situ strength.

​2.  Seasonal Moisture Contents – The use of Dynamic Cone Penetrometer (DCP) CBR results in isolation can misrepresent the functional CBR of the subgrade, given that unless the test is undertaken periodically, the seasonal moisture fluctuation may not be represented.  Additionally, if the pavement is subjected to inundation, the in-service moisture levels may be drastically underestimated.

3.  ​Cohesive Materials – Current methods of correlating the number of blows/100mm or mm/blow has not been accurately verified for non-cohesive materials (i.e. sand and gravels) and is not considered a reliable method when these subgrade materials are encountered.

How is a dynamic cone penetration test performed?
The DCP apparatus consists of a 5/8”-inch diameter steel rod with a 60 degree conical tip. The rod is topped with an anvil that is connected to a second steel rod. This rod is used as a guide to allow an 8kg hammer to be repeatedly raised and dropped from a height of 575mm. The connection between the two rods consists of anvil to allow for quick connections between the rods and for efficient energy transfer from the falling weight to the penetrating rod.

Once the test apparatus is assembled the DCP is placed at the test location and the initial penetration of the rod is recorded to provide a zeroing scale. While holding the rod vertically, the weight is raised to the top of the rod 575 mm above the anvil and dropped. The penetration of the rod is measured after each drop. In cohesive soils the penetration rod may be rotated slightly to prevent binding of the soil and the rod influencing test results. The test shall be terminated if the desired depth is reached or if the rod penetrates less than 1/8-inch in 10 drops.
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Given the nature of the test, the Dynamic Cone Penetrometer (DCP) can be used to identify bands of weaker subgrades, higher moisture contents and changes in materials and has been used historically to identify high water tables.