Online

Worley II, Robert Lee

Civil and Environmental Engineering

2022

Ph. D.

Space exploration and plans for establishing extraterrestrial habitats pose new challenges from the lack of immediate access to supplies on the Moon and Mars. In-situ resource utilization (ISRU) programs of space agencies are investigating the potential to use or augment extraterrestrial resources in support of these missions. This has expanded geotechnical interest in utilizing regolith not only to provide geotechnical functions such as foundation support and excavations, but also as a building material. This research contributes to evaluating extraterrestrial regolith as a resource through three broad themes: 1) exploring simple, non-standardized test methods for measuring low levels of soil cohesion and tensile strength in extraterrestrial regolith simulants; 2) assessing microbially induced calcite precipitation (MICP) as a technique for inducing soil improvement in terrestrial and extraterrestrial soil simulants; and (3) developing potentiometric ion-selective sensors to monitor the MICP treatment process in real-time through continuous measurements of ammonium and calcium. Lunar regolith is expected to possess small cohesive and tensile strength, under low stress conditions, which are likely to exist at the 1/6th gravity conditions of the lunar surface; the small cohesive and tensile strengths may significantly influence the regolith behavior as well as the interpretation of physical modeling experiments of ISRU processes performed on earth using regolith simulants. Therefore, cohesion and tensile strengths of lunar simulants JSC-1A and GRC-3 were evaluated using simple direct shear, vertical cut, and split box non-standardized test methods. The results provided additional insights into the yield surface in the tensile region of dry granular soils such as these lunar simulants and indicated that the yield surface is likely non-linear in the tensile range. Microbially induced calcite precipitation (MICP) is a biomineralization process which can bond otherwise loose soil particles, thereby increasing the shear strength and stiffness of the soil while decreasing its permeability and compressibility. Lunar regolith simulants were treated using a surface applied MICP treatment method. Test specimens were evaluated post-treatment via penetration testing and surface gas permeability testing. Although an increase in penetration resistance and decrease in surface gas permeability was observed as expected, the calcite distribution was stratified and skewed toward the specimen tops as the simulants contained significant fines. This result therefore indicates that MICP may work for surface erosion mitigation and dust control for soils and regoliths with fines. In addition, the MICP process was monitored during treatment in real-time using potentiometric ion-selective sensors. Although sensor calibrations indicate a strong correlation between potential and target ion concentration, fouling due to both calcite precipitation and to some extent biofouling of the sensor surfaces was observed in the highly dynamic, biomineralization environment which should be considered during data analysis.