Numerical and experimental studies of gravity effect on the mechanism of lunar excavations

In this paper, the mechanism of soil excavation in partial gravity conditions is investigated by experimental model and numerical study. Experiments were conducted in a parabolic flight, which generated different gravity conditions, focusing on the bearing capacity problem using two soil samples: Toyoura sand and Japanese lunar soil simulant (FJS-1). Corresponding numerical studies were performed by the discrete element method (DEM) for reduced gravity conditions. Herein, the DEM method was modified to include the apparent cohesion that was found in the lunar soil simulant. Two case studies were investigated by the numerical simulations: bearing capacity and soil pushing (as by a bulldozer), and for the former case comparison was made with experiment. Results show that the gravity greatly affects the ultimate bearing capacity of the Toyoura sand; however, such effect becomes insignificant in the lunar soil when the gravity is small or the soil was densely packed. By using the numerical model, this paper suggests that the ultimate bearing capacity observed in the lunar soil simulant was dominated by the apparent cohesive component, rather than gravity or friction. However, gravity causes similar effects oil both soil models ill the Soil Pushing problem. (C) 2009 ISTVS. Published by Elsevier Ltd. All rights reserved.