Vibration Mechanism and Energy Transfer Analysis of Dynamic Compaction Method on Ground with High Groundwater Level

The dynamic compaction mechanism of high-groundwater-level (HGL) foundations is still unclear, which seriously affects the engineering application of dynamic compaction in the riverbed and land reclamation. In this study, a dynamic compaction model test was established to analyze the vibration acceleration of the tamper, the soil surface, and the soil interior under different depths of groundwater level. Meanwhile, the propagation of the vibration wave was also analyzed, and the energy dissipation of dynamic compaction under the HGL foundation was studied combined with the modal damping ratio (zeta). The results showed that HGL resulted in poor foundation improvement. The main effects were the energy consumption and the friction reduction between the particles when the tamper was in contact with the water, which resulted in vibration acceleration and a sharp decrease in crater depth. The crater will not maintain its cylindrical shape, and further tamping will negatively affect the reinforcement. Vibration analysis showed that dynamic compaction results in dense soil with an increased damping ratio, but when the soil is tamped at the HGL foundation, the soil tends to oscillate, and the damping ratio decreases. In terms of energy, more than 70% of energy was dissipated directly under the tamping point of the high-groundwater-level foundation. Dynamic compaction has been extended from land foundation reinforcement to artificial reclamation foundation as an economical and environmentally friendly foundation treatment technique. The groundwater level in the coastal area is usually higher than that on land, which plays a decisive role in the success of dynamic compaction. However, there are few theoretical and experimental studies on the dynamic compaction of high-groundwater-level foundations. This paper analyzed the energy transfer and consumption of the dynamic compaction method for high-groundwater-level foundations from the perspective of vibration waves. The results showed that compared with dry sand, dynamic compaction of high-groundwater-level foundations will obviously consume reinforcement energy. Dynamic compaction causes groundwater levels to rise around the tamping point. The higher the tamping energy level, the more obvious the groundwater level rise. The results can provide a reference for expanding the treatment range of the dynamic compaction method and applying the dynamic compaction method to high groundwater foundations.