Abstract: The microstructure of soil is an important internal factor that determines its engineering properties. However, preparing suitable samples for microstructure analysis and quantifying structural parameters have always been challenging. A method of vacuum freeze drying-glue injection for preparing sandy soil samples is introduced. This method can remove water and maintain the samples’ original structure for further processing. A series of sample images with different grain sizes were taken by SEM and optical microscope, respectively. Based on the self-developed soil microstructure quantitative analysis system SMAS, the images were quantitatively analyzed. A quantitative index system composed of soil particle number, particle perimeter, apparent porosity, shape factor, equivalent diameter, fractal dimension and shape ratio were proposed and used to quantitatively evaluate the microstructure characteristics of sand soil samples. The results show that the vacuum freeze drying-glue injection method for preparing samples has the advantages of convenient operation and reliable results, which can effectively maintain original structured sand. In comparison, SEM is more suitable for the microstructure analysis of fine sand, while optical microscopy is more suitable for medium/coarse sand. SMAS can effectively identify soil particles and pores in microstructure images, providing an efficient tool for quantitative analysis of the microstructure characteristics of sand or other soils.

Key words: sandy soil, sample preparation, digital image processing, microstructure, quantitative method