济南浅层地基微观结构及分形特征研究

Study on Microstructure and Fractal Features of Shallow Ground in Jinan

天然沉积土的宏观力学特性与微观结构紧密相关,研究土体微观结构对深入揭示土的宏观力学特性具有重要意义。首先研究济南地区深度在50 m以内黄河冲积地层天然沉积土的物理力学参数分布特征,再采用场发射扫描电镜试验,分析各土层不同方向土样的微观结构特征,最后应用分形理论,研究各层土分形维数的演化规律及其与物理特性参数间的相关性。结果表明:第(7)层黄土是以粗粉粒为主体骨架的蜂窝状大孔隙结构,第(8)层粉质黏土是碎屑粉粒为骨架的蜂窝结构,第(9)、(10)和(11)层粉质黏土是以黏粒集合体为基本单元的薄层状絮凝结构。不同土层土体土粒和孔隙的分形行为明显,随着地基深度增大,土粒和孔隙的分布分维数均逐渐加大,形态分维数均逐渐减小,土粒的粒径变化比孔隙的孔径变化明显,而孔隙的形态变化比土粒复杂。土体的分维数与含水率、孔隙比、液塑限、黏聚力和内摩擦角之间存在较强的相关性。

The macroscopic characteristics of rock and soil are closely related to the microstructure. Therefore,study on the microstructure of soil to reveal the macroscopic mechanical properties of soil has extremely importance. Firstly,the distribution characteristics of physical and mechanical parameters of 50 m shallow natural sedimentary soils in Jinan area were studied and then microstructure of different soil layers in different directions were examined by FESEM tests. According to fractal theory,the microstructures of soil samples were quantitatively analyzed to explore the evolution law of fractal dimension and the relevance between basic physics parameters and fractal dimension. The results show that the 7thloess is a honeycomb-like large pore structure with coarse particles as the main skeleton; the microstructure of 8thsilty clay is a honeycomb-like pore structure with clastic particles as skeleton and the 9thto 11 thsilty clay is a thin layer of flocculation structure with the clay aggregate as the basic element. The fractal behavior of soil particles and pores is obvious. With the increase of the depth of shallow ground,the distribution fractal dimension of the particles and the pores gradually increases and the shape fractal dimension decreases. Compared with the pores,the change of diameter of particles is significant,but the pore shape is more complex than that of the particles. The soil fractal dimension has strong correlation with water content,pore ratio,liquid and plastic limit,cohesion and internal friction angle.