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Soil mechanics make clean sweep

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Soil mechanics experiment makes clean sweep

 

February 4, 1998: All six test cells were processed in an experiment to study the movement of powders, grains, and dirt in the low-gravity conditions of space. The science team is hopeful that the success of this mission, and its anticipated data, will lead to a third mission to explore soil mechanics further. (Post-flight images are available, below.)

The Mechanics of Granular Materials (MGM) experiment made its second space flight aboard the recent STS-89 mission, Jan. 22-31, 1998 (the first MGM flight was STS-79 in 1996). Three of the experiments run used quasi-static loads, which gradually compressed a column of sand contained in a latex sleeve. This built on fundamental studies started with the STS-79 mission. The other three test cells used cyclic loading and unloading which more closely resembles the vibrations experienced in soil during an earthquake. (Note that this has nothing to do plate tectonics, which happen deep underground, but with soil at or near the Earth's surface.)


Earlier stories: [MGM main story] [Mission update],

both with print-quality images


Scientists working on MGM said that the experiments went virtually without a hitch. The only problem was a pressure sensor that failed during the fourth run. A work around procedure had already been developed, so no science was lost. A quick inspection of the data cards used in the MGM experiments shows that a complete set of data was recorded for each experiment.

Following the landing, the six test cells were unloaded from Endeavour. They - plus two additional cells that were not flown or used - will be put through computer tomography (CT) scans at the facilities of EG&G Corp. at Kennedy Space Center. One of the flight test cells already was scanned before the flight."

"Follow-on experiments would allow the performance of tests with loosely-packed, saturated and undrained specimens, subjected to cyclic loading," said Dr. Nicholas C. Costes, the MGM Project Scientist and co-investigator at NASA's Marshall Space Flight Center. "This testing mode will more closely simulate soil behavior, especially during earthquakes. The specimens would have to be saturated in space. No additional hardware is anticipated at this time, only changes in the software. The experiments flown to date have been dry, medium-dense to dense, and drainage of the interstitial fluid [i.e., air between grains] was allowed to take place."

In the picture gallery below, each image links to a 576x678-pixel, 130K JPG image of the MGM test cells. These are snapshots taken after the samples were unloaded from shuttle Endeavour after landing. The top row of cells was processed through a series of five compression-relaxation cycles to extend on fundamental data collected on the first MGM mission (STS-79). The bottom row was processed through a series of compression cycles that more closely resemble the effects of an earthquake. While the bottom row was not as compressed as the top row, valuable data will be gathered from the CT scans and optical microscope examination of the sand, and from analyses of fluid pressures as the experiment was under way. (Photos by Ron Cantrell)




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Author: Dave Dooling
Curator: Bryan Walls
NASA Official: John M. Horack