A STUDY ON DETERIORATION OF DEFORMATION AND STRENGTH CHARACTERISTICS OF SATURATED CLAYS SUBJECTED TO CYCLIC LOADING BASED ON DAMEGE MECHANICS

本研究基于损伤力学的概念，研究了饱和粘土在循环荷载作用下的强度和变形特性的劣化。在两年的工程期内，对正常固结粘土和超固结粘土进行了一系列不排水循环三轴试验。第一年，通过正常固结粘土的试验结果，研究了饱和粘土在循环荷载作用下的力学性能劣化特征，并用劣化指标(损伤变量)描述了饱和粘土的劣化特征。第二年，对超固结粘土进行了不排水循环三轴试验，并考察了该方法在超固结粘土情况下的适用性。本研究的主要结论如下：(1)饱和粘土的变形特性恶化最显著的是…更巧妙地在循环加载期间和之后。因此，选择变形系数作为饱和粘土的劣化指标是合理的。(2)在循环荷载作用下，应变速率对饱和粘土的变形特性劣化有显著影响。(3)在相同的有效应力状态下，循环荷载作用下的粘土和具有静应力历史的超固结粘土的不排水强度是相同的。因此，可以用预测饱和粘土不排水强度的方法来估计前者不排水强度的劣化程度。(4)饱和粘土的变形特性劣化不仅受平均有效应力的影响，而且还受循环荷载扰动的影响。为了评价与应变历史相关的扰动对循环荷载的影响，基于损伤力学的概念，提出了一种劣化指标。(5)根据试验知识，提出了一种预测具有循环荷载历史的饱和粘土应力-应变关系的方法，并验证了该方法对随机循环荷载情况的适用性。较少

In this research, investigated was the deterioration of strength and deformation characteristics of saturated clays subjected to cyclic loading, being based on the concept in damage mechanics. For two-year periods of project, a series of undrained cyclic triaxial tests was carried out for normally consolidated clays and over-consolidated clays. In the first year, the deteriorative characteristics of mechanical properties of saturated clays subjected to cyclic loading were investigated through experimental results of normally consolidated clays, and the characteristics of deterioration were formulated in term of an index of deterioration (damage variable). In the second year, undrained cyclic triaxial tests for over-consolidated clays were performed, and the applicability of the proposed method to the cases of over-consolidated clays was examined.The main conclusions in this research are summerized as follows:(1) The deformation characteristics of saturated clays deteriorate most remark … More ably during and after cyclic loading. Therefore, it is reasonable to choose the coefficient of deformation as an index of deterioration for saturated clays.(2) The deterioration of deformation characteristics of saturated clays is influenced significantly by the strain rate on cyclic loading.(3) The undrained strengths of the clay subjected to cyclic loading and the over-consolidated clay with static stress history are the same if they are in the same effective stress state. Therefore, the deterioration of the undrained strength of the former can be estimated with the procedure to predict the undrained strength of the latter.(4) The deterioration of deformation characteristics of saturated clays is influenced not only by the decrease of mean effective stress but also by the disturbance due to cyclic loading. To evaluate the effect of the disturbance which is dependent of strain history on cyclic loading, an index of deterioration is proposed newly in this study on the basis of the concept in damage mechanics.(5) A method for predicting the stress-strain relations of saturated clays with cyclic loading history is derived through experimental knowledges, and its applicability to the cases of random cyclic loading is confirmed. Less