The 'California Bearing Ratio' (CBR) test is used to design:
Choose the correct answer
Rigid concrete pavement thickness only
Flexible bituminous pavement thickness — lower subgrade CBR requires thicker pavement (IRC:37)
Bridge and culvert design
Only for airport runway pavements
Correct Answer
B. Flexible bituminous pavement thickness — lower subgrade CBR requires thicker pavement (IRC:37)
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CBR (IS 2720 Part 16): penetration test on compacted subgrade/sub-base material (cylindrical mould, 50 mm/min loading). CBR = (test load/standard load)×100% at 2.5 or 5 mm penetration. Standard: 13.2 kN at 2.5 mm. Used for: flexible pavement thickness design (IRC:37) — higher CBR = thinner pavement. Typical values: soft subgrade 2–5%, good subgrade 10–20%, WBM sub-base 80–100%, GSB 80–120%.
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