Application of Dynamic Cone Penetrometer in Evaluation of Base and Subgrade Layers

The dynamic cone penetrometer (DCP) is one of the lowest-cost alternatives for characterization of pavement layer qualities. In addition, it is fairly easy to collect and analyze data with the DCP. The DCP is not popular in the pavement engineering community, partly because of the lack of a solid correlation between DCP results and modulus values. More than 60 DCP tests have been conducted on two test pavements used for accelerated pavement testing to assess the validities of empirical equations proposed in previous literature to compute layer moduli from data obtained with the DCP. The effect of the test procedure on the DCP test values was studied, and the moduli obtained with the DCP were compared with those obtained by falling weight deflectometer (FWD)-multidepth deflectometer (MDD) and laboratory tests. It was found that the values obtained with the DCP are dependent on the test procedure, which affects the results by at least 10 percent. If there is an asphalt concrete layer, it is preferable to conduct DCP tests through a drilled hole. A sample size of 6 is recommended for routine characterization of base and subgrade layers, because this number would achieve 95 percent confidence and an error of estimate of less than 20 percent. The moduli obtained by using the DCP and the adopted equations yielded results compatible with those obtained from FWD-MDD tests. Those equations have been recommended to the Texas Department of Transportation for further evaluation and use in routine analysis. The laboratory-determined subgrade moduli were only slightly higher than those from DCP and FWD-MDD tests. No correction factor is required for the moduli backcalculated from FWD data to match the moduli obtained in the laboratory.