Evaluation of microfabric of clay using atomic force microscopy

The term 'microfabric' (geometric arrangements of particles) was first used in the late 1960s to study features of the soil that cannot be seen with the naked eye; which includes the orientation of particles, particle size and shape, stratification and voids. It is generally believed that electron microscopy (SEM, TEM) is the only technique that can reveal particle arrangements directly. In the present study, a novel and more advanced technique, atomic force microscopy (AFM) is introduced to evaluate the microfabric of cohesive soil which is an important parameter to decide the shear strength behaviour of the soil. AFM has several advantages over SEM/TEM for characterizing particles at the sub-micron range: (i) AFM gives 3D images and 2D images with Z information, providing quantitative measurements of the soil microfabric using SPIP software; (ii) AFM images can be obtained in all environments - ambient air, liquid and vacuum. This article focuses on the use of AFM for evaluating the variation in particle size distribution, angle of orientation of particles, particle size and shape, and aspect ratio of particles due to the change in the microfabric of clay.