CALIFORNIA BEARING RATIO (CBR) METHOD Typical Testing Machine
Introduction • The California Bearing Ratio devised by engineers of the California Division of Highways in nine years period to 1938. • Most universally accepted pavement design methods. • A standard penetration-type load-deformation test is carried out, and using the values obtained from the test from an empirical design chart, the pavement thickness are calculated.
CBR LABORATORY TEST Specimen may be • Prepared • In-situ Mould • 150mm diameter • 127.3mm height • Separate base plate • A collar
The specimen is soaked and the expansion is measured. • Load is applied by the loading frame through a cylinder plunger of 50mm diameter and penetration is measured. • Rate of penetration is maintained at 1.25mm/minute. • Loads are recorded for 2.5 and 5.0mm. • Load is expressed as a percentage of the standard load at the respective deformation level, and is known as the CBR value.
CBR Equipment Soaking Samples Typical Testing Machine
CBR Equipment CBR Test – Sample Preparation CBR Test – Load-Penetration Measurement
Load a piston at a constant rate See what load it takes to make it penetrate a known amount California Bearing Ratio (CBR)
California Bearing Ratio Vs Moisture content California Bearing Ratio Equipment
CBR DESIGN METHOD • In this method, the CBR values are used to determine the total thickness of the flexible pavement and its various layers. • Following are the graphs used in the design of the pavement thickness.