Influence of sample preparation on the multi scale structure of sand-clay mixtures

Abstract

This paper focuses on the influence of sample preparation on the multi scale structure of sand-clay mixtures. Three different protocols to mix silica and kaolinite were tested in the laboratory to identify the one providing the most homogeneous microstructure. From the macroscopic to the microscopic scales, optical observation, 3D X-ray tomography, 2D scanning electron microscopy (SEM) and 2D environmental scanning electron microscopy (ESEM) were carried out on wet and dry samples. This paper provides a first insight on the mechanisms of sand clay mixing from the cm to μm scale. Preliminary results demonstrate that the microstructures of the samples prepared by the three procedures have similar macroporosities based on imaging techniques. However, the preparation which consists in mixing the sand firstly, followed by water and clay provides a more homogeneous microstructure with silica grains well-surrounded by an oriented clay layering, probably due to a geometrical effect. Understanding the formation of the oriented clay layering brings microstructural features that will help to better explain the grain displacements and rotations during direct shear tests, the behaviour at the pile sand-clay soil interfaces and to formulate sand clay microstructure models.