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

通过一系列动力模型试验研究了挤密砂桩加固软土地基的动力响应。通过使用新开发的使用线性方式系统的振动器。改良地基承受沉箱荷载。本研究所考虑的参数为S.C.P.改善的面积比和宽度、水平地震活动的震级和振动的持续时间。1.当地基经受地震时，桩中的应力与改良地基中的粘土中的应力的比率减小。但是，地震发生后，这一比例有所上升。2.沉箱底部加速度与输入加速度的比值与地基刚度密切相关。在地震发生初期，加固地基的地震反应比未加固地基的地震反应比大得多。但是，随着地震的进行，这种差异变得越来越小，这意味着加固后的地基由于受到振动而失去了刚度。3.当加固地基与未加固地基的静力安全系数相同时，未加固地基在振动作用下发生较大的沉降。地震活动性越高，振动持续时间越长，沉降越大。用常规拟动力稳定分析方法计算的动力安全系数与沉降之间的相关性令人满意。

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.