高温冻土固化前后结构性变化对融化压缩特性影响

Structural properties changes before and after solidification and their effects on melting and compression characteristics of high warm and frozen soil

摘要:

为解决高温冻土未冻水含量高、压缩性强对冻土路基造成的不良影响.以采自青藏高原粉质黏土为研究对象,从高温冻土的结构性出发,在负温环境下配置15%掺量的普通硅酸盐水泥、高性能硫铝酸盐以及普通硅酸盐水泥+高性能硫铝酸盐水泥的固化冻土试样,并通过烘干法、TDR技术、X射线衍射、扫描电镜与融化压缩试验,分析高温冻土固化前后土体总含水量、未冻水含量变化以及固化剂加入高温冻土后土体的物相成分,对比不同固化剂的固化效果,同时利用MATLAB编程开发CURVEEXTRACT图像分析系统对SEM图像进行预处理,将其导入Image-ProPlus6.0（IPP）软件中,对比分析高温冻土固化前后微观结构孔隙分布、形态以及定向性等特征.以土体孔隙定向性分维数与固化后压缩系数为桥梁,建立高温冻土固化后宏、微观之间的关系.结果表明,固化后土体总含水量减小,未冻水含量增多,由于固化剂产物的胶结作用,土颗粒整体呈现团聚状态,固化效果越好大颗粒越多,内部孔隙面积减小且孔隙由狭长状向等轴状转化,土体孔隙更加均匀化,土体孔隙定向性分维数D_f与融化压缩系数a_v之间存在良好的线性关系,固化效果越好,土体孔隙定向性分维数D_f越小,对应的压缩系数a_v越小.

Abstract:

This paper aims to solve the negative effects of the large unfrozen water content and high compression of high warm and frozen soil on the stability of roadbed. In this study, by taking the silty clay in the permafrost regions of Qinghai-Tibet Plateau as the research object, 15% ordinary Portland cement, high-performance Sulphoaluminate cement, and (ordinary Portland cement+high-performance Sulphoaluminate cement) were prepared as samples at negative temperature. The oven drying method, TDR (time domain reflectometry) technique, X-ray diffraction, scanning electron microscopy (SEM), and thawing compression test were adopted to analyze changes of the total water content, changes of unfrozen water content, and the phase composition of the soil with the addition of soil stabilizers, as well as to compare the solidification effects of different soil stabilizers. MATLAB was used to develop CURVEEXTRACT image analysis system to deal with SEM image, which was then imported to the Image-ProPlus6.0 (IPP) software to analyze the characteristics of micro pore distribution, morphology, and directivity of high warm and frozen soil before and after solidification. The relationship between macroscopical and microcosmic before and after solidification was established based on the relationship between compression property and pore orientation fractal dimension. Results show that adding soil stabilizer could reduce the total water content and increase the unfrozen water content in the soil samples. After solidification, soil particles became closer, the pore area of the soil decreased, and the pore transformed from narrow to equiaxial. There was a good linear relationship between the pore directional fractal dimension (D_f) and the coefficient of thaw compression (a_v). The better the curing effect was, the smaller the D_f was, and the smaller the corresponding a_v was.