Investigation into measuring low levels of cohesion of regolith simulants

Lunar and Martian regoliths are similar to terrestrial soils in that they appear granular but are expected to contain a small amount of cohesion. As such, cohesion in extraterrestrial regoliths pose challenges for future space operations such as In-situ Resource Utilization (ISRU). As part of preparing for human or robotic missions, it would be necessary to perform geotechnical activities similar to those typical of resource extraction on earth. ISRU requires a better understanding of mechanical properties of regoliths and to recreate those conditions for physical modeling on earth. The specific goal of this study was to evaluate two methods -- vertical cut and simple direct shear testing – and assess their efficacy in reliably measuring small amounts of cohesion in lunar simulants; JSC-1A and GRC-3. Findings indicate that vertical cut testing cohesion estimates for JSC-1A at relative densities 0-80% ranged between 0.115 kPa and 0.971 kPa and cohesion estimates for GRC-3 at relative densities 0-80% ranged between 0.190 kPa and 1.872 kPa. Additionally, results show vertical cut testing provides monotonically increasing cohesion estimates with increased relative density, but simple direct shear testing did not establish any particular trend in cohesion measurements