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Properties of Sand under Low Effective Stresses
The presentation focuses on different sets of drained and undrained cyclic triaxial experiments on loose and dense cylindrical specimens of subangular quartz sand, which were conducted under displacement control at very low effective stress levels. The experiments were motivated by the need to enhance our understanding of low-stress phenomena and mechanical properties of both terrestrial soils and regolith on the Moon and Mars subjected to low gravity conditions. The first two sets of experiments were conducted under drained conditions on NASA Space Shuttle (STS-79, 1996; and STS-89, 1998) under microgravity conditions, and the last set was recently conducted on Columbia (STS-107) in January, 2003. In the case of the drained experiments, the effective confinement pressures were held constant throughout the experiments, and they were in the range of 0.05 to 1.30 kPa, which in the case of the undrained experiments these same effective stress levels comprised the initial states. The initial relative densities of the specimens were in the range of 35% to 85%. In the drained experiments we observed peak friction angles as high as 72°±2° together with dilatancy angles in the range of 30° ±1°. Constant-volume friction angles of 34 ±1 degrees were recorded at relatively high strain levels in all the drained experiments. Transitions from a stable solid to a viscous liquid state (liquefaction) were observed in several undrained experiments at very low initial density states, however, in several cases dilative behavior was observed at very low effective stresses as well as low initial relative densities (35–45%). For several of the specimens extensive computed tomography records were obtained, which show complex patterns of shear band formation, which usually emerged at levels of 2–3% axial strain after peak strength had been reached. The presentation will focus on experimental technique, observations and data, as well as computed tomography data, and modeling results.
Properties of Sand under Low Effective Stresses
The presentation focuses on different sets of drained and undrained cyclic triaxial experiments on loose and dense cylindrical specimens of subangular quartz sand, which were conducted under displacement control at very low effective stress levels. The experiments were motivated by the need to enhance our understanding of low-stress phenomena and mechanical properties of both terrestrial soils and regolith on the Moon and Mars subjected to low gravity conditions. The first two sets of experiments were conducted under drained conditions on NASA Space Shuttle (STS-79, 1996; and STS-89, 1998) under microgravity conditions, and the last set was recently conducted on Columbia (STS-107) in January, 2003. In the case of the drained experiments, the effective confinement pressures were held constant throughout the experiments, and they were in the range of 0.05 to 1.30 kPa, which in the case of the undrained experiments these same effective stress levels comprised the initial states. The initial relative densities of the specimens were in the range of 35% to 85%. In the drained experiments we observed peak friction angles as high as 72°±2° together with dilatancy angles in the range of 30° ±1°. Constant-volume friction angles of 34 ±1 degrees were recorded at relatively high strain levels in all the drained experiments. Transitions from a stable solid to a viscous liquid state (liquefaction) were observed in several undrained experiments at very low initial density states, however, in several cases dilative behavior was observed at very low effective stresses as well as low initial relative densities (35–45%). For several of the specimens extensive computed tomography records were obtained, which show complex patterns of shear band formation, which usually emerged at levels of 2–3% axial strain after peak strength had been reached. The presentation will focus on experimental technique, observations and data, as well as computed tomography data, and modeling results.
Properties of Sand under Low Effective Stresses
Sture, Stein (author) / Batiste, Susan N. (author) / Lankton, Mark (author) / Parisi, Jill (author)
Ninth Biennial Conference on Engineering, Construction, and Operations in Challenging Environments ; 2004 ; League City, Houston, Texas, United States
2004-03-03
Conference paper
Electronic Resource
English
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