Evaluation of the Dynamic CBR Test on Coarse-Grained Materials

Abstract

Abstract The California Bearing Ratio (CBR) test is commonly used to evaluate the quality of base courses and subbase courses, subgrades, and unsurfaced roads. It provides an empirical index value for the strength of a compacted material. However, the conventional field CBR test is time consuming. As a simple and fast alternative, a dynamic CBR test has been developed for which a falling mass is used to provide the force needed for the penetration of a piston into the tested material. The biggest advantage of the dynamic CBR test compared with the conventional CBR test is that it can be completed within very few minutes. Based on experimental data from laboratory and field tests, this article evaluates the use of the dynamic CBR test on coarse-grained materials. The laboratory program consisted of 15 materials (primary and secondary raw materials) that were compacted to different dry densities and were tested using the conventional and dynamic CBR tests. Additional field tests were performed on four of these materials. The results suggest the use of the dynamic CBR test as a valuable alternative to the static CBR test on granular materials. A general correlation formula for dynamic penetration values provided by the dynamic CBR test and conventional CBR values is presented.