Micro-destructive assessment of subgrade compaction quality using ultrasonic pulse velocity

The ultrasonic pulse velocity (UPV) correlates significantly with the density and pore size of subgrade filling materials. This research conducts numerous Proctor and UPV tests to examine how moisture and rock content affect compaction quality. The study measures the changes in UPV across dry density and compaction characteristics. The compacted specimens exhibit distinct microstructures and mechanical properties along the dry and wet sides of the compaction curve, primarily influenced by internal water molecules. The maximum dry density exhibits a positive correlation with the rock content, while the optimal moisture content demonstrates an inverse relationship. As the rock content increases, the relative error of UPV measurement rises. The UPV follows a hump-shaped pattern with the initial moisture content. Three intelligent models are established to forecast dry density. The measure of UPV and PSO-BP-NN model quickly assesses compaction quality.