California bearing ratio CBR California bearing ratio is a test method to evaluate the bearing capacity of base materials proposed by California, USA. The bearing capacity is characterized by the material's ability to resist local load indentation deformation, and the bearing capacity of standard macadam is taken as the standard, and the CBR value is expressed as a percentage of the relative value. This method was later used to evaluate the strength of foundation. CBR is widely used in many countries because of its simple testing method and low equipment cost. The CBR method is used to determine the thickness of asphalt pavement, which has supporting charts and is very convenient to apply and is welcomed by engineers and technicians.
California bearing ratio tester consists of frame, loading device, force measuring device, penetration pressure head, dial indicator and so on.
In the highway test, there are records of CBR. After filling in the basic data, we can get a series of results: the result of penetration L and the result of unit pressure P. According to this series of results, these points are marked on the rectangular coordinate system with penetration L as the ordinate and unit pressure P as the abscissa. Then, according to the positions of these points, the formula of the curve is deduced by using the theory of fuzzy mathematics (linear regression). Then according to the curve, we can get the value of unit pressure P when the penetration l=2.5 and the penetration l=5.0.