华中粉砂岩粗粒土粒径级配分形特性研究

研究不同应力状态下颗粒粒径级配演化规律是分析土体应力状态、评价其工后变形的关键。基于质量-粒径分形模型从分形角度阐述了粗粒土粒径级配曲线探究依据,设计了5种不同分形维数的粒径级配,分析了土体颗粒空间分布特性;通过三轴剪切试验及颗粒筛分试验,探究了不同分形维数粗粒土偏应力峰值前后应力应变曲线性态分布及剪应力峰值、内摩擦角、分形维数因子等参数变化规律。结果表明,土体粒径范围随分形维数越大而更宽泛;应力应变曲线随分形维数及围压增大而存在应变软化向应变硬化过渡的趋势,偏应力峰值随分形维数增加而增大,内摩擦角呈先减小后增大的变化规律。粗粒土分形维数变化因子与相对围压呈线性函数关系,方程斜率及截距仍与相对围压呈线性函数关系,据此建立了考虑围压及初始分形维数的经验方程,为从分形角度来设计与优化粗粒土粒径级配而达到提高其力学强度等提供了参考依据。

Research of Fractal Feature on Siltstone Coarse-grained Soil Gradation in Central China

Studying the evolution law of particle size distribution under different stress states is the key to analyze the stress change of soil and evaluate its post-construction deformation. Based on the fractal model of mass-size particle, research basis of gradation curves for coarse-grained soil was expounded from the aspect of fractal. Then 5 kinds of gradation curves with different fractal dimensions were designed, which were used to analyze the distribution characteristics of soil particles. Conventional triaxial compression and particle sieving test were taken to study the qualitative change of stress-strain curves before and after the peak of deviatoric stress and to explore the evolutional regulation of deviatoric stress, internal friction angle and fractal dimension index by means of those samples made of coarse-grained soil with different fractal dimensions. The test results show that the wider the size range of soil particle is, the larger the fractal dimension is. Thus stress-strain curves have the trend of transition from strain softening to strain hardening with the increase of fractal dimension and confining pressure. The peak of deviatoric stress increases with the increase of fractal dimension, but the internal friction angle decreases first and then increases and then increases. The rule of fractal dimension index and relative confining pressure for coarse-grained soil can be described by linear functions, and those rake ratios and nodal increments are still the linear relationship with relative confining pressure. Therefore, the empirical equation depicted the relationship of that three factors was established. All of those exploration can be as reference basis for improve mechanical strength through design and optimize grading curves of coarse-grained soil on the point of fractal.