The California Bearing Ratio test, or CBR test, is a laboratory (or in-situ) testing method to estimate the bearing value and the mechanical strength of highway sub-bases and subgrades.
Description and test procedure
The primary purpose of theCalifornia Bearing Ratio test is to determine thebearing capacity anf the mechanical strenght of road sub-bases and subgrades. In this test, a plunger of a satandard area is pushed into the soil at a fixed rate of penetration, and the force requied to maintain thath force is measured. The CBR value is then defined as the ratio of the measured force to that required for similar penetration into a standard sample of crushed California limestone rock:
CBR=(F/Fs).100%
where F is the measured force and Fs is the force required for similar penetration into a standard sample. Higher values of CBR indicate harder surface of material. Typical values of CBR rating for different materials are (Hear 1982):
Type of soil
CBR range
Clay
1-3
Sandy clay
4-7
Well graded sand
15-40
Well graded sandy gravel
20-60
References:
Head, K. H., 1982, Manual of soil laboratory testing, Vol 2, Pentech Press, ISBN 0-7273-1305-3
Test Standards
BS 1377: 1975
ASTM D1883 procedure07e2 Standard Test Method for CBR (California Bearing Ratio) of Laboratory-Compacted Soils Link
CBR experimental results on Geotechdata.info Database:
Not available
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