An experimental micromechanical study of sand grain contacts behavior from different geological environments

Grain scale tests can provide useful information about geological materials interface properties and to understand the possible role of geological environments on their behavior. This paper presents an experimental micromechanical study investigating the behavior of two quartz sands at the grain scale, namely River sand and Beach sand which are obtained from two different geological environments. The results of the study are compared with Leighton Buzzard sand (LBS) quartz grains, with the latter material being extensively examined in previous research works. Basic characterization of the grains is conducted in terms of chemical composition, particle shape and roughness. It was observed that the grains of the Beach sand are relatively rougher and less rounded compared to the River sand grains. A custom-built new generation micromechanical apparatus was used to quantify the micromechanical behavior of the sand grains at their contacts from the two different materials. It was observed that both materials showed a similar range of Young's moduli, which are obtained from Hertzian fitting. The River sand grains showed fairly steady state behavior during shearing, which was not very obvious for the grains of the Beach sand. This different observation in steady state was attributed, partly, to grain morphology effects. The stiffness degradation of both sands followed similar trends. The average value of the inter-particle coefficient of friction for River sand and Beach sand grains are about 0.15 and 0.22, respectively, whereas for LBS grains the inter-particle coefficient of friction lies in between that of River sand and Beach sand. The high roughness and morphology of the Beach sand grains are factors which have contributed to the observed trends and the differences between the variable types of sands.