Bacteria Stabilizing Buildings Against Earthquakes

Bacteria Stabilizing Buildings Against Earthquakes



Feb 2007 - Soil bacteria 
could be used to help steady buildings against earthquakes, 
according to researchers at the University of 
California-Davis. The microbes can literally convert loose, 
sandy soil into rock, the scientists say. 
Jason DeJong, an assistant professor of civil and 
environmental engineering at UC Davis, says that when a major 
earthquake strikes, deep, sandy soils can turn to liquid, with 
disastrous consequences for buildings sitting on them. 
Currently, civil engineers can inject chemicals into the soil 
to bind loose grains together. But these epoxy chemicals may 
have toxic effects on soil and water, DeJong said. 
The new process, so far tested only at a laboratory scale, 
takes advantage of a natural soil bacterium, Bacillus 
pasteurii. The microbe causes calcite, or calcium carbonate, 
to be deposited around sand grains, cementing them together. 
By injecting bacterial cultures, additional nutrients and 
oxygen, DeJong and his colleagues found that 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, for example, to repair cracks in statues, but not to 
reinforce soil. 
The new method has several advantages, DeJong said. There are 
no toxicity problems, compared with chemical methods. 
The treatment could be done after construction or on an 
existing building, and the structure of the soil is not 
changed - some of the void spaces between grains are just 
filled in. 
DeJong and his team are working on scaling the method up to a 
practical size, and applying for funds to test the method in 
the earthquake-simulating centrifuge at UC Davis' Center for 
Geotechnical Modeling. The centrifuge is part of the national 
Network for Earthquake Engineering Simulation, funded by the 
National Science Foundation. 
A paper describing the work has been published in the "Journal 
of Geotechnical and Geoenvironmental Engineering." 
The other authors are Michael Fritzges, a senior engineer at 
Langan Engineering, Philadelphia; and Klaus Nüsslein, 
associate professor of microbiology at the University of 
Massachusetts, Amherst. The research was supported by the 
National Science Foundation. 

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