Evaluation Study of Subgrade Service Condition Based on Falling Weight Deflectometer

To make appropriate rehabilitation decisions, determining subgrade modulus of the existing semi-rigid asphalt pavements is a crucial task for highway engineers. Falling Weight Deflectometer (FWD), as a nondestructive testing technology, is an effective tool to determine subgrade modulus. The objective of this study was to establish a method to predict subgrade modulus of asphalt pavements based on Falling Weight Deflectometer. With the basic theory of structure dynamics, the finite element model of the asphalt pavement was established to generate a synthetic database of surface dynamic deflection basin parameter (DBP) indicators. Then, the relationship between DBP indicators and subgrade modulus was discussed and the prediction function for determining subgrade modulus was established. The analysis results demonstrate that subgrade modulus can be predicted by the direct deflection indicator d9, shape indicator F8 and structure layer thickness and the predicted precision is satisfied. The relative error between the theoretical value and the predicted values ranges from-13.2% to +15.56% according to subgrade modulus. The mean value of absolute relative error is 2.36%. The research results provide a technology supports to popularize FWD testing technology applied in performing subgrade structure performance evaluation.