California bearing ratio

The California Bearing Ratio test ( CBR test short ) is a test method by means of which the bearing capacity of soils and hydraulically bound layers (rarely) can be examined. The method was originally developed for fortifications of airfield surfaces and is now also in road construction for use. Basically the test indicates how much force a plunger needs to be forced into a soil sample to achieve a defined penetration speed up to a certain depth. The larger the necessary ram pressure, the higher the carrying capacity of the soil sample.

In addition to assessing the strength of statements with respect to the frost susceptibility of a soil and the effect of soil stabilization with lime can be made ​​on the basis of the test result.

Test methods

The test is carried out on a disturbed soil sample in a laboratory. The dolly with a circular cross-sectional area of 1963 mm ² is pressed at the constant speed of 1.25 mm / min in the soil sample. The maximum penetration depth is typically 2.5 mm. The test result is compared with a standard ground and formed a relationship. This percentage ratio is the CBR value again: