An Investigation on Dynamic Stability of Soft Clay Improved by Sand Compaction Piles

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A series of dynamic model tests was conducted to study the dynamic response of soft clay improved by sand compaction piles(S.C.P.) by using a newly developed shaker using a linear way system. The improved ground is subjected to caisson loading. Parameters considered in this study were the area ratio and the width of S.C.P. improvement, the magnitude of horizontal seismicity and the duration of vibration.Conclusions derived from this study are as follows. 1. The ratio of the stress in a pile to that of clay in improved ground reduces when the ground is subjected to an earthquake. However, the ratio increases after the earthquake. 2.The ratio of acceleration at the bottom of a caisson to the input acceleration is closely related to the rigidity of ground. At the initial stages of an earthquake, the ratio is much higher for improved ground than that for ground without improvement. However, the difference becomes smaller with the progress of the earthquake, implying that the improved ground loses rigidity by being subjected to vibration. 3. When the static safety factor is identical for improved ground and non-improved ground, larger settlements take place for the latter when they are subjected to vibration. The settlements are greater for higher seismicity and longer vibration duration. T he correlation between the settlements and the dynamic safety factor calculated with the conventional pseudo-dynamic stability analysis is satisfactory.