Asphalt pavement response analysis using in-situ subgrade modulus estimated from moisture contents and field deflections

The in-situ subgrade modulus at various moisture content is important for evaluating pavement performance, particularly considering seasonal variations and climate change. This study conducted a comparative analysis of in-situ subgrade modulus derived from a falling weight deflectometer (FWD) and groundwater table (GWT) and their impacts on asphalt pavement responses. The modulus derived from the measured moisture contents was used as a benchmark. Field data was collected from the long-term pavement performance (LTPP) database for comprehensive analysis. Finite element models were built for pavement response analysis. Results indicate that the GWT-predicted modulus is generally lower than or comparable with that derived from measured moisture. On the other hand, FWD-derived modulus is typically higher than the moisture-based values and the full-depth backcalculation yields the highest subgrade modulus overall. Under traffic loading, the compressive strain on top of the subgrade was greatly affected by the subgrade modulus evaluation approaches. The compressive strains calculated using GWT-predicted subgrade modulus has moderate consistency with those using subgrade modulus derived from the moisture contents (either the average modulus or modulus gradient). When using average modulus derived from FWD deflections, the resulting compressive strains varied by backcalculation method but were consistently smaller than those obtained using moisture-based modulus.