The laboratory and field compaction methods are not identical, however, comparative tests indicate that reasonable correlation of results can be obtained from field compact materials and samples compacted under similar conditions in the laboratory.
Because added strength to highly stabilized surfaces such as asphaltic concrete is neglected, the assumption of a completely saturated subgrade condition sometimes results in a too conservative factor of safety.
Because many of the procedures are of an arbitrary nature, you must run the test to exact standards in order for the design tables to be valid.
Conclusion:
beside all the limitations it is easy to perform and still does not need any big instruments etc. The value of the CBR test is then compared with the following table to get the quality of material from which the required thicknesses and other parameters are decided.