Combined SEM and computerized image analysis of clay soils microstructure: technique application

摘要

The SEM-computer system and special software techniques enabling the analysis of SEM images are being commonly used in structural studies. The software package STIMAN for the SEM-based quantitative analysis of microstructures - is an original concept developed by a team of scientists from Russia. With the application of the software package it permits a fairly precise assessment of morphometric (area, perimeter and diameter) and geometrical features (shape, anisotropy and degree of orientation) of grains and particles and pore space. Examinations in SEM require only a relatively small sample. The appropriate preparatory procedures are crucial for maintaining an undisturbed structure as well as high-quality SEM pictures which in turn are prerequisite for defining the real parameters of soil microstructure and pore space. Sampling of soils in a way as not to disturb their structure is of prime importance. Drying is one of the very important preparatory steps. During this step attention should be given to avoid soil shrinkage which can result in marked structural changes. The low temperature freeze-drying method, the basic principle of which is a rapid, simply shock freezing of a moist soil sample and successive removal of ice from the pores by vacuum sublimation. Particularly noteworthy is the procedure of vacuum impregnation of the dried soil with a luminescence polymer. A polished section is prepared from the hardened sample. Surfaces prepared in such a way can be observed in the SEM with the use of a catodoluminescence detector. To precisely examine the soil structure three sections perpendicular to each other should be analyzed. This is particularly important for soils in which an anisotropic structure can be expected. STIMAN (STructural IMage ANalysis) software is the only program which offers such full structural characteristics. The DOS version is composed of three parts: image registration, statistical data processing and data storage. Recently the same team has developed a new version under WINDOWS.