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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。
Based on the saturated fine sand dynamic triaxial test in Nanjing, it was found that the stress-strain rate curve of saturated sands changed gradually from “oval” to “dumbbell” under cyclic loading. The appearance of the “dumbbell” curve shows that saturated sand has low shear and fluidity. The average flow coefficient which reflects the fluidity of saturated sand under cyclic loading and the flow curve which reflects the change of fluidity with the vibration times are defined. It is found that the flow curve has obvious three-stage characteristics. The effects of relative density, effective consolidation pressure and cyclic stress ratio on the flow curve are given. It is proposed that the initial point of rapid growth of average flow coefficient be used as the critical point for the transition from solid state to liquid state of saturated sands, and the pore pressure ratio corresponding to the initial point of rapid growth of average flow coefficient is defined as the phase transition pore pressure ratio. The experimental results show that the average flow coefficient and pore pressure ratio curve of each condition are basically the same, the relative density, the effective consolidation pressure and the cyclic stress ratio have little effect on the phase-change pressure ratio, 0.8 or so.