Rigid layer depth setting method based on the uniformity of the backcalculated subgrade modulus

Abstract

Modulus backcalculation using falling weight deflectomer (FWD) non-destructive testing data is an important technique for evaluating the structural bearing capacity of pavements. During the backcalculation process, the rigid layer setting depth has a great influence on the results. Hence, the rigid layer depth should be accurately set. In this study, a new rigid layer depth setting model was established by layer-by-layer detected deflections from a full-scale testing road. First, the reason for the inconsistency in the backcalculated subgrade modulus based on the detected deflections was determined by analyzing the surface deflections of the subgrade layer under different load levels. Then, a new rigid layer depth setting model named equivalent thickness method was established on this basis. Finally, a comparative analysis with other rigid layer depth setting methods was carried out. It was found that the inconsistency of the backcalculated subgrade modulus was due to the unreasonable rigid layer setting depth, and the rigid layer depth could be determined by setting the total equivalent thickness of the pavement as a certain value. The comparative analysis revealed that the equivalent thickness method significantly reduced the variability and improved the conformance of the backcalculated subgrade modulus rely on the layer-by-layer deflections.