a soil bacterium that helps deposit calcium carbonate (calcite) on sandy soil could hold the key to protect buildings against earthquakes. Researchers at the University of California unravelled the wonder property of the bacteria, Bacillus pasteurii, while trying to precipitate calcite on sandy soil.
They found that calcite precipitation in sand cemented with the help of the bacteria was similar in strength to the sand cemented with the conventional chemical gypsum (hydrated calcium sulphate). Their study was published in the November 2006 issue of the Journal of Geotechnical and Geoenvironmental Engineering (Vol 132, No 11).
"The microbes, which are anaerobic bacteria found in soil, can convert loose, sandy soil into rock and hence minimise earthquake disaster," the study said. In conventional building practice, chemicals like gypsum are injected in the soil to bind loose grains of sand together.But these chemicals have toxic effects on soil and water, prompting scientists to look for an alternative.
"If sufficient native bacteria exist in the soil, they would just need to be stimulated. Alternatively, the bacteria could be injected in a solution," said Jason DeJong, a researcher.
"The treatment time will depend on the application. In the lab, it can be completed within a day. In the field, it could take between few days to few months," DeJong added.
By injecting bacterial cultures, additional nutrients and oxygen, the researchers found that they could turn loose sand into a solid cylinder.
"The method has several advantages. There are no toxicity problems. The treatment could be done after construction or on an existing building, and the structure of the soil is not changed. Only some of the void spaces between grains are filled in," the researchers said.
"It may also have applications in tunnelling, embankment and dam stabilisation, groundwater protection and aquifer storage," DeJong added.
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