Behavior of composite granular materials and vibratory helical anchors

Composite granular materials exist in many geologic settings, such as glacial tills, riverine gravels and on the lunar surface. While these materials are widely used in Civil works, they have received little attention from the research community. Thus, little is known about the physical behavior of these materials. To examine both the strength and deformation characteristics of this broad class of materials, tests were conducted on artificial composites consisting of crushed basalt combined with 1mm and 3mm glass spheres. These experiments demonstrated that the exchange of as little as 5% of the mass of the pure crushed basalt for glass spheres significantly decreases the peak strength of the material. This change in strength can be accounted for, however, by a careful consideration of the relative density of the resulting composite as compared to the pure crushed basalt. Furthermore, the stiffness of the composites at small strains was shown to be generally unaffected by the addition of the glass spheres, provided the void ratio remained constant. Good agreement was shown between the results of the elastic testing and the behavioral trends predicted by Hertz contact theory.;The crushed basalt used in this study of composites is a lunar soil simulant. Lunar equipment in the future will most likely be very small as compared to their terrestrial counterparts. Past experiments by others have shown that vibration can assist lunar equipment in near-surface excavation. Further, given the likely small mass of lunar equipment, it would be helpful if that equipment could be rapidly anchored to the lunar surface, allowing smaller equipment to handle heavier loads. With these facts in mind, experiments were conducted to investigate the behavior of helical anchors in lunar soils, and to observe whether the vibration of these anchors during installation could decrease the installation forces and work. These anchor experiments showed that the rotational or vertical vibration of the anchors during installation did not improve the installation efficiency. These experiments also provide a significant database for performance and installation modeling of anchors in the lunar surface.