Seismic stability of embankment on soft soil deposit

Well-compacted embankments resting on non-liquefiable foundation soils with a level ground surface are usually considered stable even during strong earthquake ground motions. Some case histories, however, suggest that such embankments may be damaged if the foundation soil is highly compressible, such as thick soft clay and peat deposits. An increase in the thickness of the saturated zone in the embankment and reduction of stresses of embankment soil in the saturated zone, both owing to subsidence of the embankment, are surmised as underlying mechanisms. In this study, centrifuge tests were conducted to verify this hypothesis. Two types of models – embankments on a stiff foundation soil layer and embankments on a soft clay deposit – were prepared, and horizontal base shakings were imparted. Crest settlement and deformation of the embankment during shaking were larger for the embankment on the clay.