CBR to Resilient Modulus Subgrade Calculator
Highway geotechnics & foundation engineering: Convert soil California Bearing Ratio (CBR) into resilient modulus ($M_R$) across standard empirical models (AASHTO, NCHRP, Powell) and evaluate subgrade strain.
Subgrade Soil Properties
Resilient Modulus & Subgrade Properties
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
Why does M_R = 1500 · CBR fail for gravelly soils?
The Heukelom & Klomp linear relation was calibrated on cohesive Dutch silts and clays. Extrapolating to a crushed aggregate with CBR = 80 would predict MR = 120,000 psi, which is physically impossible (unbound granular materials rarely exceed 35,000 to 50,000 psi due to confinement limits).
What is the physical definition of Resilient Modulus MR?
Resilient modulus is defined as repeated deviatoric axial stress divided by recoverable elastic axial strain: MR = σ_d / ε_recoverable, determined via triaxial cyclic laboratory loading (AASHTO T 307).
How does seasonal moisture alter subgrade MR?
During spring thaw or wet seasons, subgrade degree of saturation increases. Excess pore water pressure reduces effective stress, causing subgrade resilient modulus to drop by 40% to 60%, precipitating rapid alligator cracking in thin pavements.