The micromechanical behaviour oa a Mars stimulant soil

The overall aim of the present work is to investigate the micromechanical behaviour of a Mars Simulant granular soil, by means of grain-scale laboratory tests, and provide useful input data for future DEM analyses. Although an eye observation would suggest that the MS soil is composed of five different types of minerals, based on their colour, Energy-dispersive X-ray spectroscopy analyses have highlighted that quartz and other generic silica sand particles are the main components found within the sample. A geometrical and morphological particle characterisation was done, in order to obtain values of size, sphericity, roundness and surface roughness of the grains tested, with a reasonable accuracy. A first set of experiments was performed by means of a new custom-built inter-particle loading apparatus a the City University of Hong Kong, which allows mechanical tests at the contact between two sand particles in order to measure both the contact stiffness and the inter-particle friction coefficient. Comparisons between the curves from normal and shear loading tests and the responses modelled by means of the theories proposed by Hertz (1882) and Mindlin & Deresiewicz (1953) respectively, typically used in DEM programs, were carried out. Finally, uniaxial compression tests were carried out using a modified CBR apparatus, obtaining values of particle strength and the force-displacement curves. Weibull statistics have been applied to calculate the probability of surviving of grain splitting.