Modeling of regolith structure interaction in extraterrestrial constructed facilities.

摘要

In the near future, construction on the surface of Earth's Moon is proposed to facilitate space travel and exploration. Construction on the lunar surface will differ most notably from terrestrial-based construction in that designs of lunar constructed facilities will need to be highly exact in order to avoid excessive use of materials and on-site workmanship. This requirement creates a need for a thorough understanding of lunar soil (regolith) properties and behavior and how their variation influences the performance of extraterrestrial structures, where performance reflects the overall strength (stability) as well as the load-settlement characteristics of the foundation.;The lunar landing missions of the 1960's and 1970's (Surveyor, Apollo and Soviet-Luna) have provided a base-level knowledge of lunar regolith mechanical properties. A terrestrial-based lunar soil simulant has been developed to mimic these known properties. This simulant is used in a series of strength and deformation experiments to further investigate the nature of lunar regolith. These experiments include conventional triaxial compression (CTC), unconfined compression, reduced triaxial extension, isotropic compression, direct shear, direct tension, and self-weight unconfined tension. These experiments are used to calibrate a plasticity-based analytical model which was designed particularly for highly-dilatant granular materials under low levels of confining stress. This model, in conjunction with a finite element computer code, is used to predict the behavior of several boundary value problems. The CTC experiment is treated as a soil structure subject to end-displacement conditions, material self-weight body forces, and radially induced membrane confinement. The direct tension experiment is also analyzed as a soil-structure. It is shown that the behavior of this lunar regolith simulant is unusual in that it contains a small amount of cohesion, and markedly smaller levels of tensile strength, in the absence of water, possesses quite high angles of internal friction, and exhibits dilatant behavior for even loose material packings. Furthermore, it is demonstrated that particular care must be taken in constitutive model calibration for ultra-low levels of mean stress where the values of the small, but finite, tensile strength and cohesion become crucial.;A proposed lunar structure, used to house crew and supplies, is studied using geotechnical centrifuge principles and finite element numerical simulations. This structure consists of a very stiff hollow cylinder covered by approximately 2 m of lunar regolith in the form of a regolith-embankment used for radiation shielding. A modeling-of models approach is taken to verify centrifuge scaling relationships. The finite element simulations are found to match experiments well by providing suitable displacement boundary conditions for the bottom of the embankment.