Research on the determination of subgrade gravimetric moisture content under different compactness based on the ground penetrating radar

It is essential for improving the accuracy of subgrade compactness detection to realize the real-time determination of gravimetric moisture content during subgrade compaction. In this study, a subgrade gravimetric moisture content semi-empirical model is established to evaluate the influence of subgrade filling materials types and compactness on the subgrade gravimetric moisture content. The laboratory and field tests for different subgrade types are carried out to collect the subgrade dielectric constant under different compactness. The proposed semi-empirical model is fitted based on the experimental results and the data from the literature. The Ground Penetrating Radar (GPR) technique is then employed to obtain gravimetric moisture content by collecting the dielectric constant of the subgrade in the field test based on the proposed semi-empirical model. The results after removing anomalous data are compared with the results from the time domain reflectometry (TDR) technique. The results show that the subgrade dielectric constant subgrade increases with the gravimetric moisture content growth. And the higher compactness, the higher the dielectric constant with the same gravimetric moisture content. It can be explained that the higher compactness of the subgrade means better water retention. The proposed semi-empirical model obtains the subgrade gravimetric moisture content satisfactorily considering the types and the compactness of the subgrade, as illustrated in comparison with other models in the literature. Based on this, the GPR technique measures subgrade gravimetric moisture content more accurately compared to the TDR technique after removing anomalies. It has the advantages of not disturbing the subgrade, a wide range of applications, and high measurement accuracy, and can realize real-time non-destructive testing. This study provides a basis for determining subgrade gravimetric moisture content in real-time and non-destructive and it is important to improve the accuracy of subgrade quality evaluation.