PROPERTY EVOLUTION AND LIQUEFACTION STAGE CHARACTERISTICS OF SATURATED SAND UNDER CYCLIC LOADING
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摘要: 正确认识饱和砂土在液化过程中的性质演变规律是解决可液化土层大变形问题的关键。通过饱和砂土不排水三轴试验，研究了饱和砂土液化过程中剪应力-剪应变关系、孔压增长速率和流动性的演化规律。发现饱和砂土由固态向液态的转变过程存在显著的阶段性特征，饱和砂土的液化过程可根据孔压比增长速率特征点划分为固态、固-液过渡、触变性流体及稳定流体四个阶段，而土体的孔压比增长速率与其产生的残余剪应变相关；围压和循环应力比会影响土体液化过程中各阶段的持续时间，围压越低、循环应力比越高，饱和砂土越容易从固体阶段转变为流体阶段；饱和南京细砂从一个阶段进入另一个阶段的所需振次与对应的孔压比之间呈线性关系。Abstract: Correctly evaluating the property evolution of saturated sand in the liquefaction process is the key to solving the problem of large deformation of liquefiable soil. The undrained triaxial tests of saturated sand were conducted to study the relationship between shear stress and shear strain, the excess pore water pressure development rate and, the growth of liquidity during the liquefaction. The investigation results showed that the transformation process of saturated sand from solid phase to liquid phase displayed a significant stage characteristic. The liquefaction process of saturated sand could be divided into four stages: solid stage, solid-liquid transition stage, thixotropic fluid stage and, stable fluid stage according to pore pressure ratio development rate which is related to the residual shear strain of soil. Confining pressure and cyclic stress ratio would affect the duration of each stage in the process of soil liquefaction. The lower the confining pressure and the higher the cyclic stress ratio, the easier for saturated sand to transform from solid stage to fluid stage. A linear relationship between the required cycles of saturated Nanjing fine sand from one stage to another and the corresponding pore pressure ratio was found in this study.
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图 2
$ {\overline \kappa _N} $ 的物理意义Figure 2. Physical meaning of
$ {\overline \kappa _N} $ 
图 5 剪应变与孔压比关系曲线
Figure 5. The relationship between shear strain and pore pressure ratio
图 6 孔压增长速率、单周残余剪应变及累计残余剪应变的关系
注：①—第1阶段；②—第2阶段； ③—第3阶段；④—第4阶段
Figure 6. The relationship between pore pressure growth rate, cyclic residual shear strain and cumulative residual shear strain
图 8 表观黏度与剪应变率随振次发展
注：①—固态土体阶段；②—固液相变阶段； ③—触变性流体阶段；④—稳定性流体阶段
Figure 8. The development of apparent viscosity and shear strain rate
图 9 各工况液化前阶段性划分
注：①—固态土体阶段；②—固-液过渡阶段；③—触变性流体阶段
Figure 9. Stage division of different cases before liquefaction
图 10 孔压比增长速率与归一化振次的关系
Figure 10. Relationship between excess pore pressure ratio growth rate and normalized cycles
图 11 循环应力比和有效围压对阶段临界点及对应孔压比的影响
Figure 11. Influence of cyclic stress ratio and effective confining pressure on stage critical point and corresponding pore pressure ratio
图 12 阶段临界点振次与孔压比的关系
Figure 12. Relationship between critical cycles and pore water pressure ratio
表 1 试验工况
Table 1. Test conditions
工况 围压
$ \sigma _{ {\rm{c} }}' /{\rm{kPa} } $循环应力比
CSR工况 围压
$ \sigma _{ {\rm{c} }}' /{\rm{kPa} } $循环应力比
CSRT1 50 0.18 T4 100 0.21 T2 100 0.15 T5 150 0.18 T3 100 0.18 T6 150 0.21 
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