22 February 2007
Bacteria Used To Reinforce Buildings
by Kate Melville
Natural soil bacteria could be used to stabilize buildings against earthquakes, turning loose sand around the building's foundations into sandstone, say researchers at University of California - Davis. An article describing their work appears in the Journal of Geotechnical and Geoenvironmental Engineering.
Soils behave very differently during an earthquake, with sandy soils adopting characteristics more akin to a liquid, with disastrous consequences for any building that might be perched above. Currently, engineers can inject glue-like chemicals into the soil to bind loose grains together, but these epoxy chemicals could have toxic effects on the soil and may leech into groundwater.
Jason DeJong, of UC Davis, explained that the new process uses Bacillus pasteurii, a natural soil bacterium that causes calcite (calcium carbonate) to be deposited around sand grains, cementing them together. In the laboratory, DeJong and his co-researchers found that with the addition of bacterial cultures, nutrients and oxygen, they could turn loose, liquefiable sand into a solid cylinder.
"Starting from a sand pile, you turn it back into sandstone," DeJong said. Similar techniques have been used on a smaller scale in the past to repair cracks in statues.
The new method could offer advantages over existing chemical methods as there are no toxicity problems and the structure of the soil is not changed. DeJong's team are working on scaling the method up to a practical size and testing it in the earthquake-simulating centrifuge at UC Davis' Center for Geotechnical Modeling.
Source: University of California - Davis