Dynamic compaction of a thick soil-stone fill: Dynamic response and strengthening mechanisms

A large-scale field test to investigate vibration velocities from dynamic compaction of soil-aggregate mixture in a fill at a Chengde airport construction site, China, was carried out. The propagation and evolution of the vibration waveforms, wave amplitudes, and wave frequencies were analyzed and the mechanism by which the strength of the soil-aggregate fill was reinforced by the tamping energy was studied. The results show that there are only two vibration forms, shock waves and vibration waves, in the soil-aggregate mixture under dynamic compaction. The dominant vibration frequency and optimum frequency band for dynamic compaction are determined and the concept of critical elastic vibration velocity for soil-aggregate mixtures is proposed. A method for determining the magnitude of this vibration is demonstrated. During and after compaction, the fill could be divided into three zones, an impact reinforced zone, plastic stress wave reinforced zone, and elastic area in which the soil is not reinforced. These zones are defined by the spatial distribution of the vibration velocities and the correspondingly increased soil densities. Finally, the dynamic compaction reinforcement mechanism for a coarse-grained soil-aggregate mixture is explained and the reinforcement process is divided into two stages. In addition, a suggestion for the best layer thickness for dynamic compaction of fill is proposed.