CBR test (California bearing ratio test).

Описание: 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.

procedure-

The CBR test is a penetration test in which a standard piston, with a diameter of 50 mm (1.969 in), is used to penetrate the soil at a standard rate of 1.25 mm/minute.

Although the force increases with the depth of penetration, in most cases, it does not increase as quickly as it does for the standard crushed rock, so the ratio decreases. In some cases, the ratio at 5 mm may be greater than that at 2.5 mm.

If this occurs, the ratio at 5 mm should be used. The CBR is a measure of resistance of a material to penetration of a standard plunger under controlled density and moisture conditions.

The test procedure should be strictly adhered to if a high degree of reproducibility is desired.

The CBR test may be conducted on a remouldes or undisturbed specimen in the laboratory.

The test is simple and has been extensively investigated for field correlations of flexible pavement thickness requirement.


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.

If a soaked (wet) measurement is desired, the specimen in the mould is soaked in water for four days and the swelling and water absorption values are noted.

The surcharge weight is placed on the top of the specimen in the mould and the assembly is placed under the plunger of the loading frame.