Professor Dixon has been carrying out research on acoustic emission generated by deforming soil since the late 1980s. The focus of activity has been detecting slope movements and specifically with providing an early warning of instability.
The first major field study was ‘Assessment of acoustic emission (AE) techniques for monitoring the stability of slopes’ carried out 1992 to 1995 funded by EPSRC (project GR/H80156). A novel approach was developed using AE monitoring of active waveguides. Deformation of the soil slope resulted in straining of the active waveguide system (steel tube with granular backfill surround) leading to generation of AE. Initial field trials monitoring AE over discrete time periods proved that slope deformations can be detected using active waveguides (Kavanagh 1997, Dixon et al. 2003), and can detect ground movements before traditional techniques (e.g. using inclinometers). However, monitoring was carried out over short time periods during site visits, data was post-processed and it was not possible to use AE rates to quantify displacement rates. Following this initial study, an extensive laboratory investigation was undertaken to develop AE processing and interpretation strategies that can be used to provide information on the relationships between AE and slope deformation rates (Kousteni 2002, Spriggs 2005, Dixon and Spriggs 2007).
This research led to an EPSRC funded project on ‘Assessment of Landslides using an Acoustic Real-time Monitoring System (ALARMS)’ (project EP/D035325). The ALARMS project was the logical next step to develop existing laboratory instrumentation to enable real-time field monitoring with the aim of producing a rigorous practical early warning system. The project was carried out November 2005 to May 2009. It developed and deployed a real-time AE monitoring system at the Newcastle University EPSRC funded BIONICS test facility (project GR/S87430). Nine active waveguides were installed in the slopes of the BIONICS embankment. Monitoring demonstrated the robustness of the measuring system (i.e. minimal false alarms). The embankment slopes did not deform during the monitoring period and therefore validated through comparison of measured AE and measured displacement rates using inclinometers could not be achieved. The system used at BIONICS employed a high cost multi-channel A to D board in conjunction with a PC, which allowed central monitoring of all nine waveguides.
The promising field results obtained from the BIONICS project led to development of the concept of using relatively low cost, unitary, battery operated sensors for acoustic emission slope monitoring. A UK patent application was submitted ‘Apparatus and method for monitoring soil slope displacement rate by detecting acoustic emission’ (GB 2467419) and this was granted 18th May 2011.
EPSRC Follow-on Funding was obtained to develop the unitary low cost sensor concept. The project started in July 2009 and was completed in June 2010. Funding was awarded jointly to Loughborough University (project EP/H007261/1) and the British Geological Survey (project EP/H00730X/1). A formal collaboration agreement was formed between Loughborough University and the British Geological Survey (BGS) in order to benefit from BGS expertise in the development of geophysical sensors and instrumentation systems for robust field applications. The follow-on fund project designed and built unitary acoustic slope displacement rate sensors and demonstrated their performance in a field trial. Waveguides were installed through the active natural landslide at Hollin Hill in North Yorkshire and the sensors used to monitor AE generated by the deforming slope over the winter period 2009/10. AE rates were compared to displacement rates measured using traditional instrumentation and clear correlations obtained. The results of this trial demonstrated the sensitivity of AE sensors to rapid changes in slope displacement rate, which is the primary requirement of a monitoring system if timely warnings are to be given.
Funding from the EPSRC Knowledge Transfer Account funded the production of additional sensors by the BGS in 2011 and the establishment of a field trial in a rail way cutting landslide, supported by Geotechnical Observations Ltd and Network Rail. EPSRC/Finance South East Collaboration Funding (project EP/1502041/1) in 2011/12 extended the collaboration with BGS to allow re-engineering of the sensors to improve performance and to establish a field trial on the Yorkshire coast at Flat Cliffs supported by Halcrow (CH2M) and Scarborough Borough Council. Extension of the field monitoring was made possible by award of an Innovation Fellowship to Professor Dixon in 2013 from the East Midlands Development Agency European Regional Development Fund. Since 2013, field monitoring has been supported by the Loughborough University Enterprise Project Group and a number of stakeholder collaborators in the UK, Austria, Italy and Canada, including funding from Monmouthshire County Council, Austrian Research Council, OeBB (Austrian Railway), Canadian Pacific and Canadian National Railways (see the Case Study and Collaborators pages).