The 2011 Civil Engineering Winner - Slope ALARMS

Slope Alarms

Loughborough University, Geotechnical Observations, British Geological Survey

Landslides are a hazard all over the world, killing thousands of people every year and causing expensive damage to critical infrastructure. And, worryingly, partly down to the growing frequency of extreme weather events and uncontrolled development in some of the world’s most populous areas, they are becoming more common.

In many countries, it’s rare for slopes to be routinely monitored due to the high cost of instrumentation. But, in response to calls from the UN for the development of early-warning systems that could be deployed in low-income economies, a group led by Loughborough University has developed a low-cost sensor system that is able to predict whether a landslide is likely to occur.

Working alongside the British Geological Survey and Geotechnical Observations, the Loughborough-led team has developed the Slope Acoustic Landslide Real-time Monitoring System (ALARMS), a sensor-based technology that can be embedded in the soil and that is able to detect the high-frequency acoustic emissions (AE) generated by deforming materials. All materials emit noise when they deform. A significant part of the noise emitted by deforming materials is at a frequency higher than can be detected by the human ear. The Slope ALARMS sensors monitor AE generated as soil grains move against each other. As there is always some initial movement before a landslide occurs, this can be used to provide an early warning. The sensors only detect the high-frequency AE – this reduces false warnings, because everyday noise is excluded. The system is able to compare the frequency of this noise with a set of trigger values and generates an alarm if they are exceeded.

The development of the system has had to overcome a number of key challenges. A slope monitoring system must be able to provide warning of a landslide early enough to enable action to be taken. It must also be robust, so that there are no false warnings, as these increase the possibility that real warnings will be ignored.

The sensor comprises a transducer, amplifier, filters, signal processing, data storage, communication and power components. The sensor quantifies detected AE and converts it into displacement rates, so that it can be compared with trigger values and an alarm raised if these are exceeded. The sensor is located on an active waveguide. This comprises a steel tube surrounded by granular soil backfill and is installed in a borehole that penetrates an existing or potential shear surface beneath a slope. Deformation of the slope strains the waveguide (i.e. the granular backfill), generating AE. Relationships between AE and displacement rates are derived through laboratory calibration. If trigger values are exceeded, an alert message is sent to nominated persons to enable relevant action to be taken. Further collaboration between Loughborough University, the British Geological Survey and Geotechnical Observations has attracted Knowledge Transfer Account and EPSRC/Finance South East Collaboration funding to undertake proof-of-concept field trials of the sensor and to develop a commercialisation strategy.

This has the potential to save thousands of lives and to improve the quality of life of millions of people

The work is underpinned by research carried out by Prof Neil Dixon and Dr Matthew Spriggs from Loughborough University, who carried out the first field trials of an acoustic real-time slope monitoring system and established the principles of operation for a low-cost unitary sensor. A UK patent has been granted for the unitary sensor.

Phil Meldrum and Edward Haslam, of the British Geological Survey, designed and built the first research unitary battery-operated, low-cost Slope ALARMS sensors with wireless communication capability. Their expertise in the design of geophysical instrumentation for use in extreme weather and at remote sites was crucial to the production of robust sensors that could operate for many months. Key challenges included power consumption, wireless communication and continuous operation. The research sensors have been deployed at several sites where slope instability was anticipated. They have operated continuously at sites for periods in excess of 12 months and these trials are continuing. Meldrum and Haslam are currently re-engineering the sensor to reduce power consumption and reduce cost of manufacture. These sensors will be trialled on sites over the 2011-12 winter.

Geotechnical Observations, said to be an expert in the use of instrumentation to analyse slope stability through installation of instrumentation, also played a key role in the project and actively supported the selection of trial sites, installation of Slope ALARMS sensors and evaluation of performance.

Proof-of-concept field trials of the sensors, where they are being compared with traditional techniques, are currently in progress on a Network Rail cutting, a large rock slide in the Italian Alps, a coastal landslide on the Yorkshire coast, a natural landslide in Yorkshire and the BIONICS research embankment at Newcastle University. Plans are also well advanced to instrument a landslide on the M25 and a road cutting in Northern Ireland.

The group plans to commercialise the sensors and is looking at ways of further reducing the cost of the technology so that it can be widely deployed in the developing world. This has the potential to save thousands of lives and to improve the quality of life and standard of living of millions of people whose social and economic wellbeing is compromised by the dangers presented by the extreme environments in which they live and work.