British scientists and engineers have created a device that may save lives in Costa Rica and other countries where landslides are common. The device is a new type of sound sensor system.
Thought to be the first system of its kind in the world, it works by measuring and analyzing the acoustic behavior of soil to establish when a landslide is imminent so preventative action can be taken, said the Engineering and Physical Sciences Research Council.
Noise created by movement under the surface builds to a crescendo as the slope becomes unstable and so gauging the increased rate of generated sound enables accurate prediction of a catastrophic soil collapse, the council said.
Costa Rica has had six months of rain-soaked hillsides collapsing, sometimes with fatal results. Such slides are typical of the country’s rainy season. And they come without warning.
The new device has been developed by researchers at Loughborough University, in collaboration with the British Geological Survey, through two projects funded by the Engineering and Physical Sciences Research Council.
The detection system consists of a network of sensors buried across the hillside or embankment that presents a risk of collapse. The sensors, acting as microphones in the subsoil, record the acoustic activity of the soil across the slope and each transmits a signal to a central computer for analysis, the council said.
Noise rates, created by inter-particle friction, are proportional to rates of soil movement and so increased acoustic emissions mean a slope is closer to failure, the council noted. Once a certain noise rate is recorded, the system can send a warning, via a text message, to the authorities responsible for safety in the area. An early warning allows them to evacuate an area, close transport routes that cross the slope or carry out works to stabilize the soil, the council said.
The system is now being developed further to produce low cost, self-contained sensors that do not require a central computer. This work is focused on manufacture of very low cost sensors with integrated visual and/or audible alarms, for use in developing countries, the council said. Ongoing work includes field trials, market research and planning commercial exploitation of the technology.
Materials undergoing deformation underground create acoustic stress waves, known as acoustic emissions. Gathering data on the emissions will provide information on the presence and location of straining, according to the council, adding:
The project team’s sensor, for which Loughborough University has submitted a patent application, was developed to capture these acoustic emissions below the surface. It consists of a piezo-electric transducer that sits on top of a steel tube, called a wave guide, buried in the slope. The transducer converts the energy in the acoustic emissions into an electrical signal which is recorded by computer.
The wave guide sits within a borehole filled with gravel which moves in response to any strain or deformation within the slope. Movement of the gravel creates noise which is transmitted to the surface, and the transducer, via the steel tube.
The length of the wave guide is determined by the distance of the unstable subsoil under the surface and so can be tens of meters long, if necessary.
Monitoring is conducted at frequencies too high for the human ear to detect, which ensures background noise does not lead to false alarms, the council said.