Robust, quick, and cost-effective in situ testing of sub-grade materials below pavements
The Dynamic Cone Penetration (DCP) test is widely used in pavement and road infrastructure investigations. It is a valuable method for evaluating the in situ resistance of materials and determining the structural properties of sub-grade materials beneath road pavements.
Designed by the Transport Research Laboratory, and often referred to as the TRL DCP, the test offers numerous benefits. These include robustness, ease of use, speed, cost-effectiveness, and the ability to detect varying layers within the sub-grade. When results are plotted cumulatively, the DCP test can provide insights that traditional in situ tests may miss.
The equipment’s compact nature makes it suitable for use in areas with restricted access. While it typically investigates only the top strata of soil up to 3m depth, its simplicity allows for a large number of tests to be performed at closely spaced intervals over extensive linear distances. This makes it a valuable tool in road infrastructure design, particularly for identifying areas with low sub-grade strengths that may require closer attention.
The test procedure involves driving a metal cone into the ground by repeatedly striking it with an 8kg weight dropped from a height of 575mm. After each blow, the penetration depth of the cone is measured and recorded. This provides a continuous measurement of penetration resistance up to a depth of 3m. The test concludes either when the desired depth is reached, or the rod is unable to penetrate further.
Correlations have been established between DCP results and in situ California Bearing Ratio (CBR) measurements. These enable the interpretation and comparison of results with highway or pavement design specifications.
In pavement design, the DCP test helps estimate sub-grade strength. Quick penetration typically indicates poor strength or insufficient compaction, suggesting the need for thicker pavement layers or improved compaction. Conversely, a high number of blows resulting in minimal penetration indicates a competent or well-compacted sub-grade.
