The standard loads used for calculation of CBR are:

Explanation:

California Bearing Ratio (CBR):

• The California bearing ratio test is used to evaluate the suitability of subgrade and the material used in sub-base and base course.
• It is measured to indicate the relative strength of paving materials and not the absolute strength.
• CBR test is a strength test conducted on the soil by introducing surcharge load at the compaction rate of 1.25 mm per minute on a completely soaked soil sample passing through 20 mm sieve size.
• The test results have been correlated with the thickness of the various materials required for the flexible pavement.

\({\rm{CB}}{{\rm{R}}_{\rm{\delta }}} = \frac{{{{\rm{P}}_{\rm{\delta }}}{\rm{\;of\;soil}}}}{{{{\rm{P}}_{\rm{\delta }}}{\rm{\;of\;standard\;crushed\;aggregate}}}} \times 100\)

δ = displacement in mm

Pδ = Load corresponding to ‘δ’ settlement

Ps = Load for standard crushed aggregate:

At 5 mm penetration Standard load Ps = 2055 kg  

At 2.5 mm penetration standard load Ps = 1370 kg