Investigation on Adjustment Factor of AASHTO Subgrade Resilient Modulus Prediction

AASHTO (1993) predicts the backcalculated subgrade resilient modulus on an existing flexible pavement as a function of load applied, surface deflection at a ratio of radial distance to 0.7 of radius of stress bulb at the subgrade - pavement interface least one. This paper reports the investigation on the accuracy of the predicted subgrade resilient modulus. From the investigation, the ratio of radial distance at least 1.5 is a better limit. The prediction is improved after an adjustment factor. For thick pavement structures, adjustment factors depends on the pavement structure, it is greater than 1.2. For other cases, with the ratio of radial distance greater than 4.0 the adjustment factor is more stable in a range of 1.06 to 1.10. For the ratio of radial distance in a range of 1.5 to 4 which is more practical for daily routine evaluation, the adjustment factor is in a range of 1.06 to 1.20, and the proposed adjustment factor to be used for pavement evaluation is 1.15.