饱和黄河岸滩粉土循环荷载后的变形强度特性

摘要

A number of triaxial compression tests with stress-controlled monotonic loading and post-cyclic monotonic loading were carried out on saturated silt in the Yellow River floodplain under the condition of consolidated undrained. The influence of cyclic stress amplitude, confining pressure and cyclic loading-in-duced pore-water pressure ratio on post-cyclic mechanical behavior of silt are investigated. A post-cyclic monotonic loading stress-strain model of silt has been established, in which the confining pressure and cy-clic loading-induced pore-water pressure ratio can be considered synthetically. It was found that the effect of cyclic stress amplitude on post-liquefaction mechanical behavior is little for the same cyclic loading-in-duced pore-water pressure ratio. The effective stress critical state lines are unique under monotonic and post-cyclic monotonic loading independent of cyclic loading history. Both the post-cyclic undrained shear strength and initial tangent modulus degrade compared to that under the monotonic loading. The degradation of initial tangent modulus is more marked than that of strength. The degradation level increases with increas-ing pore-water pressure ratio caused by cyclic loading. The post-cyclic undrained strength ratio and initial tangent modulus ratio as well as failure stress ratio are only function of pore-water pressure ratio generated by cyclic loading for different confining pressure. The post-cyclic stress-strain relationship can be described by hyperbolic model. The results predicted by the model are in good agreement with the experimental data.%对黄河岸滩饱和粉土在固结不排水条件下进行了一系列单调加载、循环荷载后单调加载的三轴试验，研究了动应力幅值、围压及动孔压比对循环荷载后力学特性的影响，提出了可考虑围压及动孔压比影响的粉土循环荷载后单调加载应力应变关系的变形模式。试验结果表明：循环荷载作用完全液化时，动应力幅值变化对液化后力学特性的影响很小；循环荷载后单调加载的有效应力临界状态线与单调加载时相同，不受循环荷载作用历史的影响。与单调加载时相比，循环荷载后的不排水强度及初始切线模量皆产生衰化，衰化程度随动孔压比的增大而增大，初始切线模量的衰化程度更明显；不同围压下循环荷载后的不排水强度比、初始切线模量比及破坏比，皆与动孔压比之间有良好的归一化关系；粉土循环荷载后的应力应变关系可以用双曲线模型来描述，模型计算值与试验实测值基本吻合。