Embankment structures in Japan have been subjected to a large number of earthquakes and as a result some of them leads to the failure of embankments. Therefore it can be unavoidable to develop the evaluation of seismic performance and the seismic design to constructed embankments. At present embankment is constructed fundamentally by managing degree of compaction Dc (%) at higher water content than the optimum water content wopt (%). However, it is pointed out that the difference of water content at compaction has some effects on mechanical characteristics of compacted soil even if the same degree of compaction is obtained. Furthermore, it has been gradually revealed that the mechanical characteristics can be remarkably improved due to achieving as the high degree of compaction as possible.
Keeping in view the above, a series of cyclic undrained triaxial tests was carried out on compacted and saturated sandy-silt soil, which was actually adopted as a dike material. The specimens were prepared by compaction at the different water content with various compaction energy Ec (kN/m3) in order to compare with effects of compaction condition such as the degree of compaction and water content on seismic characteristics. Experimental results show that the samples compacted at lower water content than the optimum water content wopt (%) are stronger than the samples compacted at higher water content than wopt under the same degree of compaction. It is also confirmed that the deformation due to cyclic loading develops rapidly at drier side of wopt rather than at wetter side of wopt. Thus, it is inferred that seismic performance of embankment greatly relies on some factors such as degree of compaction and water content.
