Work out pavement design (cbr) instantly with clear inputs, formula shown and shareable results.
The CBR method sizes a flexible pavement from soaked subgrade strength and cumulative standard axles. Thickness grows with the logarithm of traffic and falls as CBR rises, scaled here from a 400 mm reference for 10 msa on a CBR 5 subgrade. The correlation E = 17.6 CBR^0.64 converts CBR to an elastic modulus for mechanistic checks.
Total thickness
T mm = 200 x (log10 msa + 1) x (5 / CBR)^0.4
Subgrade modulus
E MPa = 17.6 x CBR^0.64
Preliminary estimate only. Pavement design must follow the design guide adopted by the road authority and be verified by a qualified highway engineer.
T mm = 200 x (log10 msa + 1) x (5 / CBR)^0.4. The CBR method sizes a flexible pavement from soaked subgrade strength and cumulative standard axles.
Because the design condition is the worst credible moisture state. A subgrade tested at optimum moisture can show three times the soaked CBR and would produce a dangerously thin pavement.
This calculator takes 3 inputs: Soaked subgrade CBR, Cumulative design traffic, Bituminous layer thickness. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.