Abstract
The mixing order of silica sand, clay (kaolinite), and water controls the microstructure of resulting artificial soil samples. Most homogeneous microstructures can be achieved by applying the mixing order “sand-water-clay.” The following methods were used to validate this statement: (1) optical observation, (2) X-ray tomography, (3) scanning electron microscopy, and (4) Mercury intrusion porosimetry. For all samples, clays are mainly organized in a homogeneous matrix but are also dispersed heterogeneously in micrometer-sized layers surrounding sand particles, particularly where sand grains show a greater roughness. At water contents ≥1.5 w L , the microstructures are visually similar from the mm to μm scale whatever mixing order is used. However, for water contents lower than 1.5 w L , the mixing order controls the distribution of the clay particles. This paper proposes a motivated choice of a preparation protocol of artificial clayey materials to be used in laboratory experiments. It might contribute to better understanding and modeling grain movements and arrangements in artificial muds, used for instance in underground mining, foundation settlement, hydraulic containment, road construction, soil stabilization, and in natural soils in the occurrence of soil liquefaction, industrial brick manufacturing, and in studying shear processes in tectonic fault zones.
Highlights
Understanding the rheological behavior of soils provides insights to improve the design and long-term stability of construction foundations, roads, and artificial drilling muds
Sand-clay mixtures are commonly employed as simplified and reconstituted soils in the laboratory to investigate the thermo-hydro-mechanical behavior of clayey soils [13, 19,20,21,22,23,24,25,26,27]. e macroscopic behavior of soils is usually known to be controlled by the microstructure, which was examined by several studies [28,29,30,31]
A clay matrix around sandy particles and as a discontinuous micrometer layer around the sand in humid and dry samples. is discontinuous clay layer is possibly caused by several effects of (a) the shape of sand particles, which while rotating, bring about clay particles to spread on their surface; (b) the heterogeneous roughness of sand particles: sand cavities capture clay particles during their rotation [93, 94], and (c) the desiccation process at 105°C: the viscous clay matrix shrinks while surrounding the grains [56]
Summary
Understanding the rheological behavior of soils provides insights to improve the design and long-term stability of construction foundations, roads, and artificial drilling muds. It allows a better quantification of the risks of soil liquefaction and shrinkage and swelling disorders below civil engineering structures [1,2,3,4,5,6,7]. Sand-clay mixtures are commonly employed as simplified and reconstituted soils in the laboratory to investigate the thermo-hydro-mechanical behavior of clayey soils [13, 19,20,21,22,23,24,25,26,27]. Vallejo and Mawby [21] prepared dry sand-clay mixtures by shaking samples in sealed plastic bags until visual homogeneity; Polidori [38] by Advances in Materials Science and Engineering adding deionized water into the mixture, the mixture was placed in an oven at 60°C to eliminate humidity absorbed from the atmosphere before being mixed; Bendahmane et al [39] and Marot et al [40] mixed sand and water at a water content of 8% for three minutes and clay powder was added progressively during mixing
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