A FIELD STUDY OF IN SITU CALIFORNIA BEARING RATIO AND DYNAMIC CONE PENETROMETER TESTING FOR ROAD SUBGRADE INVESTIGATIONS

Field tests were carried out to determine the repeatability of results obtained from both the in situ California bearing ratio (CBR) test and the Scala dynamic cone penetrometer, and the correlation between results of both tests. Testing was carried out under field conditions so results are those expected under such conditions rather than under ideal laboratory-type conditions. The materials tested consisted of a subgrade of mottled clay in which iron nodules had developed and an imported subgrade of yellow clay with sandstone nodules. Results indicated that the coefficient of variation of a CBR for the particular material at one test location could be of the order of 60 per cent whilst that of the cone penetrometer could be of the order of 40 per cent. The correlation between the two tests was found to be best represented by an inverse relationship. It was also found that, for the material tested, in situ results were generally lower than those obtained in the laboratory from samples compacted at field moisture content and density. (Author/TRRL)