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California Bearing Ratio test is done for determining the bearing capacity of soil or bitumen pavement.
The CBR is a penetration test used for determining the subgrade strength value of pavements and roads.
These results of tests are used with help of curves to determine the pavement thickness and various subgrade layers.
Purpose of California bearing ratio test:
The main purpose of the California bearing ratio test is the measurement of a soil resistance penetration before reaching its highest ultimate value of a shearing Basically, 2 California bearing ratio value is designed as a ratio in % of range 0 to 100. The important operation of conducting the California bearing ratio test are same of variations of various soil conditions and various type of construction. California bearing ratio test is used for the evaluation of subgrade strength of road and pavement California bearing ratio value used as an index of soil strength and its bearing capacity The results obtained from the CBR test are used with the Imperial curves for the determination of the thickness of pavement and various component layers of pavement.
The purpose of doing a CBR test is to find out the California Bearing Ratio (CBR) of a material which has to be used for the subgrade of flexible pavements. The actual quantity that concerns the strength of the subgrade material is Resilient Modulus though. CBR is different from it but hugely corellated. Also, in literature there are curves plotted for the CBR against the expected traffic (million axles per year) for every subgrade thickness. We can read the required thickness for which we need to design the subgrade layer if we know the CBR of our material and the design traffic. So, it is preferred not to get into the complexity of resilient modulus calculation and use CBR instead which can be easily tested on site.
By definition, CBR is the ratio of the opposing bearing stress experienced by a standard penetrator when penetrated by a distance of 2.5 cm into the rock to the actual crushing strength of the rock in percentage.
