中文摘要：

循环荷载作用下,饱和软黏土将发生应变软化现象.而以往的研究中往往忽略土体的各向异性固结对软黏土循环软化特性的影响,并且以往对循环软化的研究大多采用低频循环荷载方式.通过对杭州饱和软黏土进行应力控制的循环三轴试验,研究循环次数、循环应力比、固结比、频率、超固结比对土体应变软化的影响.试验结果表明,循环次数的增加,循环应力比的提高,都将加快土体软化;循环荷载作用下,软黏土存在临界循环应力比,当循环应力比较小或较大时,软化指数与lgN近似为线形关系,而当循环应力比在临界循环应力比左右时,两者表现为明显的曲线关系.随着频率的提高、土体超固结性的增强,土体软化程度降低.当土体为各向异性固结时,在循环应力比较小的情况下,随着固结比的增加,软化指数逐渐减小;当循环应力比较大时,在循环初期,土体的各向异性固结加速了士体的软化,但随着循环次数的增加,各向异性固结土体的软化指数逐渐要大于各向同性固结土体.同时,在试验的基础上推导反映土体软化规律的经验公式,利用该公式并结合修正的Iwan模型对软黏土的动应力-应变关系进行描述.

英文摘要：

Degradations of stiffness and strength will occur in soft clay under cyclic loading because of the generation of pore pressure. Unfortunately, previous work rarely incorporates the effect of anisotropic consolidation on cyclic degradation behavior of soft clay, In addition, most of the previous tests were performed with a lower cyclic frequency when considering strain softening. The strain degradation characteristics of saturated soft clay subjected to undrained cyclic triaxial loading is investigated at different cyclic numbers, cyclic stress ratios, consolidation ratios, overconsolidation ratios and frequencies of cyclic loading. It is observed that the degradation index reduces with the progressive cyclic numbers and the increase of cyclic stress ratio. There is a critical cyclic stress ratio in clay subjected to cyclic loading, When the cyclic stress ratio is much higher or lower than the critical cyclic stress ratio, the relationship between degradation index and lgN is linear. However, when the cyclic stress ratio is around critical cyclic stress ratio, a nonlinear relationship is observed. On the other hand, higher frequency and overconsolidation ratio decrease the degradation index of soft clay. For anisotropic consolidated clay, the degradation index reduces with the increase of consolidation ratio at a lower cyclic stress ratio. At a higher cyclic stress ratio, the degradation index of anisotropic consolidated clay will be greater than that of normally consolidated soils with increasing cyclic numbers. A nonlinear relationship is obtained if the degradation index is plotted against the cyclic numbers on a semi-log scale.This relatlonsnlp nas been synthesized in the form of an empirical equation. This empirical equation is further used to describe the dynamic stress-strain relationship of saturated soft clay according to modified Iwan＇s model.