The primary purpose of conducting the CBR test is to evaluate the mechanical strength so that the wheel loads can be easily replicated.A sample of soil is taken with the help of a plunger in an area that has been predetermined by the engineers in a standard area using a spherical piston at 1.25 mm/min.
Method of Conducting CBR Test
The test of CBR is conducted with the help of measuring the pressure which is needed to effectively penetrate the sample of soil in the area that has been predetermined, as well as standardized. In general, 3 different specimens of almost equal weight (7kg in approx) are required to be compressed so that the compactness can be achieved in the range of 95% to 100%. After this, the weight of empty mould is recorded.
Out of the 3 specimens that have been used, the first specimen is termed as the primary specimen. In this, the water is added and then, it is subjected to be filled with water, so that it can be compacted into 5 different layers using 10 blows. After this process is completed on the primary specimen, its collar is removed and it is levelled to surface. This is done in order to calculate the total content of moisture that has taken place and shown its effect.
This primary specimen is then taken to the weight of the mould. Similarly, the other samples are also taken in the same pattern and the different readings are noted down. The swell readings are used so that they can tell about the amount of swell can be calculated after a duration of 3-4 days. Moreover, the mould is also removed for the water to get drained.
When a load of penetration and readings are scrutinized and the related graphs are drawn between the penetration and load penetration, then the value of CBR is determined. This leads to the drawing of the final graph in which the percentage CBR and Dry Density are evaluated. It will produce the required degree of compaction which plays a key role in the testing of CBR. One key thing that plays a major role here is the inclusion of the right kind of apparatus. Some of the popular apparatus that are used for this purpose are surcharge weight, dial gauges and penetration plunger.
