Bearing capacity of shallow foundations in a low gravity environment

As a basic study for future lunar/planetary explorations and the in-situ resource utilization missions, bearing capacity characteristics of shallow footing systems in a low gravity environment were investigated. A series of model loading tests on a simulated lunar soil (lunar soil simulant) and Toyoura sand were conducted on an aircraft that flew in parabolic paths to generate partial gravity fields. As a result of the model tests, it became clear that bearing characteristics, including the coefficient of subgrade reaction and ultimate bearing capacity of the lunar soil simulant in a low gravity environment is hardly influenced by the gravity levels, while Toyoura sand exhibits a high dependence on gravity. From the observation of the failure mechanisms, it was found that the gravity dependence seems to correlate well with soil compressibility. To rationally explain the dependence of ultimate bearing capacity on gravity, theoretical evaluations were attempted in the framework of the upper bound method. The proposed calculation method not only makes it possible to correlate quantitatively the failure mode with dependence on gravity, but also may allow us to predict the ultimate bearing capacity in the lunar surface environment.