Evaluation of Instability and Residual Deformation of Soft Cohesive Soils under Earthquake-induced Cyclic Lording

基于粘性土循环和直-单剪切试验的室内试验结果，以及软土地基上路堤性状数值分析模型的考虑，指出：(L)三轴不排水循环加载引起的粘性土的刚度和强度退化与循环加载时观测到的剪切应变的大小唯一相关。2)利用SADAP动力响应分析程序进行了数值分析，得到了以最大加速度和超固结比(OCR)为参数的地震沉降量预测设计图。通过与软基河堤离心机试验结果的对比，验证了设计图版的实用性。3)数值分析结果也以设计图版的形式给出，以预测地震时堤坝或地基是否失稳。4)通过数值分析和离心机试验的结果，认为预压或堆载是提高软基河堤稳定性的有效措施。

Based on the results from laboratory investigation using cyclic and direct-simple shear tests on clays and their consideration into modeling for numerical analysis of behavior of embankments on soft ground, the following is pointed out :l) Degradation of stiffness and strength of cohesive soils triggered by undrained cyclic loading in triaxial conditions can be uniquely correlated to the magnitude of shear strain observed during cyclic loading. This is common with normally consolidated and overconsolidated specimens.2) Numerical analysis using a computer program for dynamic response analysis called SADAP incorporating the above-mentioned finding was carried out to obtain the design chart for predicting the earthquake-induced settlements as a parameter of the maximum acceleration and the overconsolidation ratio (OCR). A practical availability of the design chart was proved by comparing with the settlements observed in the results of centrifuge tests on the river dyke founded on soft clay.3) The results from numerical analysis were also given in the from of the design chart to forecast whether the dyke or the ground leads to instability during earthquakes.4) Through the results not only from the numerical analysis but also from the centrifuge tests, the effectiveness of preloading or surcharging was recognized as a countermeasure for increasing the stability of river dykes founded on soft clay.