Automated time lapse electrical resistivity tomography for monitoring embankments (ALERT-ME) is a two-year project undertaken by the BGS that began in April 2010. It is supported by the East Midlands Development Agency (emda) via the Single Programme fund.
The BGS has enlisted representatives from the Great Central Railway (Nottingham), Network Rail, London Underground, British Waterways and G Underwood to help steer the project and focus applications towards the long term stability of engineered earthworks.
BGS have also enlisted the support of the Transport iNet to showcase ALERT-ME with a knowledge exchange event planned for early 2012, once the project has been established.
This project seeks to advance the commercialisation of prototype ALERT technology as an early warning system for monitoring the physical integrity of vulnerable earth structures (e.g. embankments and cuttings) within the transport network. A field-scale demonstration study is an essential prerequisite to exploitation and commercialisation.
The ALERT technology uses permanent in situ electrode arrays and permanent instrumentation.
The system can be interrogated remotely from the office by wireless telemetry (satellite, GPRS, GSM/3G, internet) to provide volumetric images of the subsurface in real time, thereby eliminating the need for expensive repeat surveys or inspections.
This non-invasive technology will monitor the internal physical condition of engineered earthworks using diagnostic imaging methods, analogous to those used in medicine, such as computerised tomography scans (CT) or magnetic resonance imaging (MRI).
The project will demonstrate the application of ALERT technology for the real-time monitoring of strategically important and at risk earthworks (i.e. embankments and cuttings) within the transport network.
The overall aim of the ALERT-ME project is to provide early warning of potential failure events, and hence aid strategic planning and design of low cost, targeted preventative maintenance to ensure the long-term stability of earth structures. This strategy will lead to significantly more efficient use of scarce maintenance resources and underpin sustainable construction within the UK’s transportation network.
Resistivity sensors are combined with geotechnical and environmental point sensors to aid the in situ calibration of the resistivity images. The great benefit of resistivity imaging is that it can provide high-resolution volumetric information on subsurface structure, and when used in time-lapse mode, provides differential images to monitor changes in the moisture content of earthworks.
Data is transmitted, processed, stored and displayed using dedicated BGS servers and a secure web-portal. The entire process from data capture to visualisation on the office PC is automated and seamless — allowing unprecedented time-series images to be captured with no manual intervention.
This will provide the basis of a commercial web-based bureau service which will enable asset owners to remotely assess the physical integrity of important earthworks 'on demand'. The resulting resistivity images and associated calibration data will enable threshold moisture levels to be established to give early warning of instability.
The system will inform proactive strategies for targeted, preventive maintenance. The prototype ALERT technology has been installed on a section of Great Central Railway (GCR) embankment, near East Leake, Nottinghamshire. An advisory panel comprising transport sector stakeholders provides steerage and help to assess the cost-benefit of this approach compared to existing railway and waterway inspection procedures.
Dr David Gunn
Team leader — Geotechnical & Geophysical
Properties & Processes
Email: Dr David Gunn
Dr Jonathan Chambers
Team leader — Geophysical Tomography
Email: Dr Jonathan Chambers