Geotechnical Aspects of Extraterrestrial Regolith Simulants

Geotechnical engineering has been crucial to the success of construction projects on Earth, and now it is time to extend this expertise to other celestial bodies. As NASA planned the Apollo missions, geotechnical engineers conducted extensive studies to understand the properties of lunar soil, using analogs like volcanic ash and other terrestrial materials to simulate the moon's surface. Nevertheless, it was not until the inception of the year 1968 that the Surveyor landers were able to give the first actual estimates of the moon soil geotechnical characteristics such as bearing capacity, void ratio, etc. With the development of more refined regolith simulants based on samples returned from the Apollo 11 Mission in 1969, geotechnical engineers managed to assess further and more complex varieties of properties indoors in earthbound laboratories. The objective of this doctoral work is to mechanistically characterize the physical and mechanical properties of twelve lunar and one Martian regolith simulant provided by NASA. In order to do so, a comprehensive experimental program was designed to mimic unbound granular material compacted states behavior in the laboratory. The focus was on determining the resilient properties, strength parameters, and deformation potential of these materials. Different from prior studies, this dissertation undertook a large set of interrelated geotechnical tests demonstrating significant variability based on factors such as load application rates and magnitudes, density state, and compaction methods. The experimental work demonstrated the existence of the noticeable strain rate dependency on the strength parameters for the simulants tested at various relative compaction levels. Further, it was found that the strength degradation was also greatly dependent on breakage of these simulantsâ?? particles. This underscores the importance of nonlinear and anisotropic regolith modeling for accurately determining orthogonal strength characteristics, settlement potential, and the stability of platforms for planetary construction. These results are of high relevance to lunar and Martian missions and infrastructure expansion since they equip engineers with knowledge of how to build structures that will survive the moon and mars conditions thereby promoting safety and sustainability of future missions. Finally, a series of numerical analyses employing finite and discrete element methods were performed to model the behavior of lunar and Martian surfaces subjected to dynamic loading from planetary rovers. The main aim of these simulation series was to predict dust emission and to characterize the anisotropic nature of the surface regolith using the geotechnical properties tested in the laboratory as input parameters.