On seismic behavior of unsaturated fill dam models

A series of centrifuge shaking table tests was conducted to investigate the seismic behavior of unsaturated fill dam models. Two models consisted of different materials were used in centrifuge model tests: one with No. 6 silica sand and the other with a mixture of No. 6 silica sand and artificial silt with a dry mass ratio of 2:1. The effect of soil wetness on the seismic behavior was evaluated by changing the initial water content. In the tests, accelerations, surface deformations, pore water pressures (PWP), pore air pressures (PAP), and displacements within the models by using PIV method were measured. For the models constructed with silica sand only, when the water content was low, deformation with slip failure was observed. Large PWP oscillation occurred during shaking regardless of the water content against our expectations. Such behavior has not been monitored. The magnitude of the oscillation was slightly greater in the silica sand model than in the mixed soil model and positive PWPs remained only in the silica sand models after the tests. The oscillation of PAP during shaking was fairly smaller than that of PWP and therefore appeared to have little effect on the behavior of the dam. When a mixed soil model with varied water contents, 12% in upstream and 5% in downstream of the dam model, was used, vertical downward displacement occurred in the low-water-content region near the dam axis. Displacements occurred within the upstream side were larger than those within the downstream. The dam model moved toward upstream in the upstream region, while it moved toward downstream side with dominant downward movements in the downstream region. Compression occurred at the bottom of the dam model and was particularly high near the slope toe of the downstream side. Thus, the behavior of the mixed soil model depended on the difference of water contents.