Coating effects of nano-sized particles onto sand surfaces: Small strain stiffness and contact mode of iron oxide-coated sands

The presence of nano-sized particles on the surface of sand grains can significantly influence the mechanical, physical, and chemical behavior of the sand because of the effects of contacts between particles. This study quantified the change in small strain stiffness caused by the presence of iron oxide particles (hematite and goethite) that were chemically sorbed onto uncemented silica sand. Particularly, the change in contact mode between sand particles, caused by the presence of the nanoparticles, was studied. The iron oxide coating density of coated sands was controlled by changing the substrate sand particle size, ranging from 0.11 to 0.72 mm in diameter, with corresponding iron contents ranging from 0:13 mg iron oxide/g sand (goethite) to 6.4mg iron oxide/g sand (hematite). The presence of the iron oxide nanoparticles altered the contact mode between particles and, correspondingly, the small strain stiffness as a function of the initial relative density, applied stress, iron content, and substrate particle size. The macroscale experimental results were analyzed via contact mechanics (i.e., Hertz and Mindlin contacts) to gain a more fundamental understanding of changes that iron oxide coatings make on the behavior of sand.