The California Bearing Ratio (CBR) is a measure of the strength of the subgrade of a road or other paved area, and of the materials used in its construction.
[2] Penetration is measured by applying the bearing load on the sample using a standard plunger of diameter 50 mm at the rate of 1.25 mm/min.
The CBR measures a material's resistance to penetration of a standard plunger under controlled density and moisture conditions.
The test is simple and has been extensively investigated for field correlations of flexible pavement thickness requirements.
[3][4] The laboratory CBR apparatus consists of a mould of 150 mm diameter with a base plate and a collar, a loading frame and dial gauges for measuring the penetration values and the expansion on soaking.