Use and interpretation of the dynamic cone penetrometer (DCP) test

Abstract

During the early 1930's the California Bearing Ratio test (CBR) was developed for the testing of material strength in the laboratory for the design of pavements. The test involves the compaction of a potential road-building material into a standard mould under a standard compaction effort at predetermined moisture content, soaking the mould for 4 days and then penetration with a standard plunger at a fixed rate. The loads required to penetrate to selected depths are then compared with those necessary to penetrate a standard material and a CBR value is obtained. The procedures for the determination of the Maximum Dry Density (MDD), Optimum Moisture Content (OMC) and CBR are given in TMH11. In the test, all stones greater than 19 mm diameter are removed (sometimes replacement fines are added), the material is compacted under a dynamic impact load and the material is then soaked. In the field the coarse aggregate remains, the material is normally compacted under a vibrating force and the material seldom becomes soaked. The test results are thus really incomparable with the actual conditions, which are likely to prevail in the field. The CBR test has been adapted for the field using a portable CBR but it is difficult and time consuming and is seldom done because of the equipment needed and the fact that the moisture content changes with time.