When earthquakes strike in sandy soil, the ground can turn to a liquid-like state that proves disastrous for buildings. The phenomenon, called liquefaction, is common around bays and near the sea. It destroyed several buildings in low-lying areas in the 1989 Loma Prieta earthquake in San Francisco.
Now scientists hope to turn such sandy soils into solid rock by injecting live bacteria into the ground.
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Civil engineers already know they can inject chemicals into loose soil to bind grains together. But the chemicals are toxic.
A natural culture of Bacillus pasteurii along with oxygen and other nutrients causes calcium carbonate to form around sand grains, cementing them together. The structure of the soil is not changed; the gaps are simply filled in.
"Starting from a sand pile, you turn it back into sandstone," said Jason DeJong, an assistant professor of civil and environmental engineering at the University of California at Davis.
The culture is not toxic, DeJong and colleagues said. And it could be applied during or after construction.
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The process has been tested only in a lab setting, however. A similar technique has been used to repair cracks in statues.
The researchers plan to test the process on a larger scale if funding is provided. The scheme is detailed in the Journal of Geotechnical and Geoenvironmental Engineering and was funded by the National Science Foundation.
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