Correlation between the dynamic cone penetration index and the Falling Weight Deflectometer-determined subgrade resilient modulus

Modern pavement design characterizes the subgrade soil in terms of the resilient modulus. This parameter is determined in a non-destructive in-situ method using the falling weight deflectometer (FWD) and in the laboratory from the repeated load triaxial test. These methods however are both expensive and time consuming and are not readily available in most highway departments in developing countries. On the other hand, the simple and inexpensive dynamic cone penetrometer has been extensively used for pavement in-situ subgrade characterization. This paper reports on an attempt at a correlation between the results of the Dynamic Cone Penetrometer test and the output of the Falling Weight Deflectometer (FWD) test for purposes of estimating the subgrade resilient modulus. Fifty-two FWD deflections and Dynamic Cone Penetrometer field tests were conducted on sections of an urban arterial road in Accra, with varying terrain. Soil samples were also recovered from trial pits sunk at selected locations and subjected to standard laboratory tests for purposes of identification and classification. The results of the output of the FWD sensors were analyzed and correlated with the DCP penetration index. The results suggest that the DCPI may be used to predict the subgrade resilient modulus.