Bacterium makes buildings earthquake-proof

Microbe solidifies unstable soils by carbonate incorporation

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Soil bacteria could help to stabilize buildings against earthquakes. Californian scientists have found that certain microbes can solidify loose, unstable subsoil into rock.

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A strong earthquake can transform deep, sandy soils into a soft, fluid-like swamp within seconds. As a result, the floor under the foundations of the houses flows away, buildings sink or tilt. Engineers are tackling this today by adding chemicals to potentially dangerous substrates that bind and stabilize the loose grains of soil. However, these epoxy chemicals are toxic and contaminate soils and groundwater.

Jason DeJong, professor of environmental engineering at the University of California at Davis, has now discovered together with colleagues that a soil bacterium, the unicellular Bacillus pasteurii, could remedy this situation. The microbe causes calcium carbonate to deposit around the sand grains of the subsurface and "cement" them together. In laboratory experiments, the researchers have already tested the ability of this bacterium. Only by adding a bacterial solution, nutrients and oxygen did they convert such loose sand into a solid rock cylinder.

"Start with a pile of sand and turn it into sandstone, " explains DeJong. Similar techniques have been used in the restoration of cracks in reliefs and statues, but not for the stabilization of soils. However, according to the researcher, the new method has several advantages: First, there are no environmental problems due to the toxicity of the substances. On the other hand, this method could be used even if a foundation or building already stands, because the structure of the soil is not changed. The bacterium only fills some of the voids between the grains of calcium carbonate. display

Next, DeJong and his colleagues want to work to scale the method from laboratory to scalable.

(University of California - Davis, 22.02.2007 - NPO)