Landslide prediction tool uses fibre-optic sensors

New technology may be able to predict when a landslide is imminent by detecting small shifts in soil, researchers in Italy say.

Fibre-opticsensorsembedded inshallow trenches within slopes couldhelp detect and monitor both large landslides and slow slope movements.

Usually, electrical sensors have been used for monitoring the risk of landslides, but these sensors can be easily damaged. Fibre-optic sensors are more robust, economical and sensitive, say researchers at the department of industrial and information engineering at the Second University of Naples.

A widely used monitoring technique used around the world involves installing an inclinometer inside a borehole. The instrument measures angles of slope, elevation, or depression of an object with respect to gravity. The new technology, however, has a few advantages over electrical sensors.

The fibre-optic sensors placed in the ground bendwith any shift in the land mass and registerthe movement as a loss of light.

'Nervous system' of a slope

"Distributed optical fibre sensors can act as a nervous system' of slopes by measuring the tensile strain of the soil they're embedded within," said Prof.Luigi Zeni, whose team will be presenting the new tool on Oct. 21 at a conference in Tucson, Ariz., held by the American Physical Society Division of Laser Science and the Washington-based Optical Society

Taking it a step further, Zeni and his colleagues worked out a way of combining several types of fibre-optic sensors into a plastic tube that twists and moves under the forces of pre-failure strains. Researchers are then able to monitor the movement and bending of the optical fibre remotely to determine if a landslide is imminent.

The use of fibre-optic sensors "allows us to overcome some limitations of traditional inclinometers, because fibre-based ones have no moving parts and can withstand larger soil deformations," Zeni said.

These sensors can be used to cover large areas several square kilometres to pinpoint slope failures or early deformations.

The cables can identify locations where something anomalous occurs with the precision of a few metres and detect a change in length of one centimetre over one kilometre," Dr. Zeni told CBC News.

"Furthermore, they can be interrogated from a remote point with no need of inspections of the monitored area," he said, adding that the data can be transmitted via wireless networks or optical fibre networks.

Zeni said large-scale installations of the system could be put in place within one year at locations that have yet to be determined.

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Its estimated that every yearlandslides kill more than 4,500 people and injure thousands of others around the world. They are stark examples of how nature can wipe out entire communities within seconds.

The landslide that struck Vargas state in Venezuela in December 1999, for example, killed as many as 30,000 people and erased entire towns from the map without warning. Two weeks of non-stop rain had weakened one side of the Avila mountain, causing the slide.