So, you must check if the final SN3 is similar to the assumed SN. Higher SN means stronger pavement, thus the impact of traffic on pavement deteriorations is less. Roadbed soils (Subgrade material) CBR (California Bearing Ratio), R-value (Resistance), and Mr (Resilient modulus) are used to describe the property of the subgrade material.Materials of construction (Base course), a2Base!Structural number of the base course, a2Use CBR, R-value, or Mr to find a2 values Materials of construction (Subbase), a3 Charts are available to convert the properties of pavement construction materials to structural numbers: a3, a2, and a1Structural number of the subbase, a3Use CBR, R-value, or Mr to find a3 values The following conversion formulas are used if either CBR or R-values are given.Mr (lb/in2) = 1500 x CBR for fine-grain soils with soaked CBR of 10 or less.Mr (lb/in2) = 1000 + 555 x (R-value) for R During the structural design, only Mr values are used. Materials of construction (AC surface), a1= Resilient modulus, MrStructural number of the AC surface, a10.44Įnvironment Temperature and rainfall affect the level of strength of the subgrade, reflected on the value of resilient modulus. AASHTO developed a chart that helps you to estimate the effective roadbed soil resilient modulus using the serviceability criteria (in terms of relative damage, uf.) Determine the average uf.

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