3 February 2023

Soil microbes are a valuable resource. Including in case of earthquake

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Nitrogen gas emitted by microbes helps stabilize soil by preventing building collapse during seismic events, US research shows. Encouraging this process means avoiding concrete injections while reducing damage to the environment

by Matteo Cavallito

 

The importance of microbes in maintaining soil balance is widely known. Microorganisms, in fact, contribute to the protection of soil fertility and regulation of the carbon cycle in addition to shaping several other aspects that characterize the ecosystem as a whole. A list of essential functions, in short, which, according to some researchers, also include an additional and surprising ability: the protection of buildings during earthquakes.

The hypothesis is advanced by a group of scientists from the University of California Davis and the University of Arizona. Microbes, explains a study conducted by the two universities, are able to counteract soil instability. Exploiting this property, the researchers say, allow for new methods of securing that are significantly less damaging than traditional methods.

Soil liquefaction

During earthquakes, experts recall, shaking causes what is known as “soil liquefaction.” The soil, in other words, takes on liquid-like behavior by losing strength and rigidity, making buildings and other structures likely to collapse. The most widely used technique to counter this phenomenon to date is permeation grouting, which involves injecting concrete into the ground. However, this method has several shortcomings.

The system, in fact, requires the use of a lot of water, a scarce resource in some seismic areas such as California, for example. And it indirectly releases a significant amount of carbon dioxide through the production of concrete.

Scientists have thus hypothesized the use of an alternative method: microbial desaturation. Whenever it is consumed by soil bacteria, the authors explain in a statement from the California university, nitrogen is released in a gaseous state and ends up filling the space between sediment grains, acting as a shock absorber when earthquakes occur. This process can be accelerated by specially injecting nitrate into the soil.

The effectiveness of desaturation by microbes

Microbe-induced desaturation, the study notes, “is an appealing alternative to current ground improvement technologies since it can be employed underneath existing structures with minimal disturbance, is expected to be less resource intensive than current techniques and does not significantly alter soil properties.”

This technique, in particular, represents “an attractive alternative to permeation grouting considering environmental metrics (e.g., global warming potential, disturbance) and cost.”

The use of desaturation, in fact, “reduces the global warming potential of the ground improvement project by 15 times and the life cycle cost of MID is less than half of permeation grouting.” Previous studies, conducted through field trials and modeling, the authors say, have finally shown that the method is effective in stabilizing soil for up to 20 years.

Environmental benefits

“Microbially induced desaturation is a more sustainable alternative to hazard mitigation: it outperforms permeation grouting across various impacts, including global warming potential and cost,” said Aisha Faruqi, a researcher in the Department of Civil and Environmental Engineering at the University of California Davis. The gas emissions released by microbes, in fact, “aare less than four percent of what is produced from permeation grouting because of grouting’s heavy use of carbon- and water-intensive cement.”

Unlike grouting, finally, induced desaturation uses on-site groundwater without requiring additional water resources. Concrete production, Faruqi says, requires twice the amount of water used in the microbial process and subtracts potable water resources.