Analysis of Experimental Results on the Bearing Capacity of Sand in Low-Gravity Conditions

With advancements in space exploration, operations in low-gravity environments such as the lunar surface are expected to be conducted. Geotechnical engineering problems such as those associated with the foundation bearing capacity considerably influence the feasibility and safety of these operations. In this study, the findings of experiments conducted by Japan Aerospace Exploration Agency (JAXA) scientists on parabolic flight, aimed at measuring the ultimate bearing capacity of shallow foundations under 1/6 g to 2 g of gravity, are analysed. Specifically, the results are analysed to calculate the ultimate friction angle based on the classical Terzaghi limiting equilibrium solution in soil mechanics. The friction angle of foundation sand increases as the gravity level decreases. This finding is verified through advanced arbitrary Lagrangian-Eulerian (ALE) finite element simulations based on a simple Mohr-Coulomb model. Moreover, the underlying mechanism for this phenomenon is examined considering an ALE finite element simulation based on a newly developed rheological model known as the Tsinghua-MiDi sand model. The pressure-sensitive and rate-dependency constitutive behaviour of sand is clarified. Notably, this phenomenon increases the viscous shear stress and ultimate friction angles in low-gravity conditions. The coupled effects of the loading rate and low-gravity level on the bearing capacity of foundation sand are predicted. The findings can provide a novel theoretical prospective for geotechnical studies in space exploration engineering in low-gravity conditions.