中文摘要：

基于南京饱和细砂动三轴试验发现，循环荷载下饱和砂土应力-应变率曲线形状随孔压累积由“椭圆形”渐变为“哑铃形”。“哑铃形”关系曲线的出现表明饱和砂土具有低抗剪性和流动性。定义了反映循环荷载下饱和砂土流动性的平均流动系数以及反映流动性随振次变化的流动曲线，发现流动曲线具有明显的三阶段特征。给出了相对密度、有效固结压力和循环应力比对流动曲线的影响规律。提出以平均流动系数急速增长初始点作为饱和砂土由固态向液态转变的临界点，据此定义平均流动系数急速增长初始点对应的孔压比为相变孔压比。试验发现，各工况的平均流动系数与孔压比关系曲线基本一致，相对密度、有效固结压力和循环应力比对相变孔压比几乎无影响，各工况相变孔压比均在0．8左右。

英文摘要：

Based on the dynamic triaxial tests on the saturated Nanjing fine sand, an obvious phenomenon is discovered that the relationship curves of the shear stress-strain rate are altered from an elliptical shape to a dumbbell one with the build-up of the pore water pressure. The relationship curve with the dumbbell shape demonstrates that the saturated sand possesses low shear resistance and fluidity. The average flow coefficient and the flow curve describing the fluidity of the saturated sand under cyclic loading are defined. It can be found apparently that the three-phase characteristics exist in the flow curves. The influences of the relative dense, effective consolidation pressure and cyclic stress ratio on the flow curves are discussed. It is presented that the initial sharply-increasing point for the average flow coefficient is taken as the critical point of the saturated sand changing from the solid state to the fluid one. The pore water pressure ratio corresponding to the initial sharply-increasing point is defined as the pore water pressure ratio of phase change. The tests show that the relationship curves of the average flow coefficient and the pore water pressure ratio under various loading conditions are similar in shape. In addition, the pore water pressure ratios of phase change for the saturated Nanjing fine sand under various test conditions are about 0.8. The relative dense, effective consolidation pressure and cyclic stress ratio have few influences on the pore water pressure ratios of phase change.