黏-砂混合土压缩特性与微观结构特征关系研究

黏-砂混合土在吹填土地基中广泛应用,混合土地基变形与微观结构息息相关。为探讨黏-砂混合土压缩变形的微观机制,以黏土与砂不同配比的混合土为研究对象,利用压缩、扫描电镜(SEM)试验和图像处理技术(IPP)对固结前后试样的颗粒排列、孔隙分布进行定性和定量分析,从微观层面探讨了混合土微观结构随固结压力变化的演变机制。结果表明:随着含砂量的增大,混合土孔隙比呈先减小后增大的趋势,压缩系数不断减小;大、中孔隙随着含砂量增大明显增多,颗粒间接触方式从以边-面、面-面接触为主向点-点、点-面接触过渡;固结作用提高了颗粒排列的密实性和有序性,孔径分布向小孔径范围移动,大孔隙面积占比最大降幅达31.39%,中孔隙面积显著增加,对微、小孔隙影响不明显;土体颗粒的定向概率熵与和含砂量呈正线性相关,与压缩系数a_1-2呈负线性相关,含砂量越大,混合土颗粒排列越混乱,定向概率熵越大,其压缩性越低。由此可见,固结压力和配比不同引起的颗粒、孔隙微观结构参数变化是导致混合土压缩特性差异的内在原因。

Relation between Compression Characteristics and Microstructure of Clay-Sand Mixtures

Clay-sand mixture is widely used in dredger fill. The deformation of mixed soil foundation is closely related to its microstructure. To explore the microscopic mechanism of compression deformation of mixed soils, we analyzed in qualitative and quantitative scales the particle arrangement and pore distribution of clay-sand mixture samples before and after consolidation via compression tests, scanning electron microscopy (SEM) tests and Image-Pro Plus (IPP) image processing. Results revealed that with the increase of sand content, the void ratio of mixed soil reduced at first and then grew, and the compressibility decreased gradually. The sensitivity of each pore group to consolidation pressure is closely related to sand content. With the increase of sand content, the number of large and medium pores increased, and the contact mode between particles transferred from edge-face and face-face contact to point-point and point-face contact. Compression enhanced the compactness and orderliness of particle arrangement. Pore size tended to be smaller. The percentage of large pore area dropped up to 31.39%, which resulted in the expansion of middle pores; however, the impact on micro-and-small pores is not obvious. The directional probability entropy of soil particle is linearly correlated with sand content, while negatively linearly correlated with compressibility coefficient a_1-2. Lager sand content led to the more chaotic arrangement of mixed soil particles, larger directional probability entropy, and smaller compressibility. In conclusion, the change of microstructure parameters of particles and pores caused by different consolidation pressure and sand content ratio is the internal reason for the difference in the compression characteristics of mixed soil.