Engineering Propeties of Simulated Lunar Soils

To provide basic engineering data on the behavior of soils under lunar environmental conditions, experiments were performed to determine the properties of soils believed to be representative of the lunar surface materials under vacuum levels to the 10^-10 torr range. Experiments consisted of the determination of the porosity attained by the soil when deposited under various vacuum levels and the effect of vacuum on the shear strenth parameters. It was observed that under low vacuum levels the porosity that the soil attained was less than in atmosphere, after which it increased for higher vacuum levels. Direct shear tests showed the internal friction to increase under vacuum whereas the effect on the apparant cohesion depended on the mineralogical compostion. These effects of vacuum were attributed to the development of interparticle forces resulting from the removal of adsorbed gas layers from the surfaces of the soil grains.