Living Reference Work Entry

Encyclopedia of Engineering Geology

Part of the series Encyclopedia of Earth Sciences Series pp 1-2

Date: Latest Version

California Bearing Ratio


The California bearing ratio (CBR) is an index that compares penetration resistance of laboratory-compacted soil material to that of a durable, well-graded (poorly sorted), crushed rock material.


The test was developed by the California Department of Highways in the late 1920s with the intention to characterize cohesive soil in the subbase and subgrade of pavement sections. It is a standard test with procedures specified by American Association of State Highway and Transportation Officials (AASHTO 2013) and American Society for Testing and Materials (ASTM 2016) in North America. The test uses a standard compaction mold with a diameter of 152.4 mm and a height of 177.8 mm. The degree of compaction and range of moisture content are specified for the test depending on project requirements. In most cases, the sample is compacted into the mold and then submerged in water for 4 days prior to testing. The sample and mold are removed ...

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