CBR test Calculation

 

CALCULATIONS

Stress-Strain Curve –Plot the stress (resistance to penetration-depth of penetration) curve for each specimen as shown in Figure2. In Some instances, the initial penetration takes place without a proportional increase in the resistance to penetration and the curve may be concave upward. To obtain the true stress-strain relationships, correct the curve having concave upward shape near the origin by adjusting the location of the origin by extending the straight-line portion of the stress-strain curve downward until it intersect the abscissa (see dashed lines)

California Bearing Ratio- The corrected load values shall be determines for each specimen at 2.54 and 5.08 mm (0.10 and 0.20 in.) Penetration. California Bearing Ratio values are obtained in percent by dividing the corrected load values at 2.54 and 5.08 mm by the standard loads of 6.9 and 10.3 MPa (100 and 500 psi), respectively, and multiplying these ratios by 100.

 

 

CBR = corrected load value x100/

Standard Load

 

The CBR is generally selected at 2.54 mm (0.10 in.) penetration. If the ratio at 5.08 mm (0.20 in.) penetration is greater, the test shall be rerun. If the check test gives a similar result, the ratio at 5.08 mm (0.02 in.) penetration shall be used.