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Mining Subsidence detected and mapped by InSAR

InSAR was first applied to the mapping of mining subsidence in 1996, in collaboration with the Marconi Research Centre, Matra Marconi Space and RJB Mining UK. This worldwide lead is still maintained by EnviroScience. Subsidence has been imaged and deformation profiles fed back data to geotechnical models (Fig 9.10.11). This technology has been applied in Eastern and Western Europe and South Africa where surface deformation due to a deep mine rock burst seismic event (Richter 5.6) recorded by the US Geological Survey was the first man made recorder seismic event imaged. Processing was by collaboration partners at the University of Cape Town - Radar Remote Sensing Group.

Coherent Target Monitoring (CTM) can now be applied to mining subsidence to enable continuous monitoring of scattered coherent targets such as were found on the Selby Coalfield, UK. CTM surveys thousands of coherent targets in a satellite scene simultaneously, in satellite passes normally repeated every 35 days, or exceptionally every 6-10 days with multiple orbit tracks. Millimetre accuracy comparable to GPS is indicated in trials and validation of CTM by the Canadian Geological Survey

Selby Coalfield - Yorkshire UK

Fig.9 Selby Coalfield Differential InSAR, Fig.10 Detail of Fig.9 with mine workings plan overlai, Fig. 11 Feedback to subsidence modelling. Note match of InSAR to model output contours. Small differences enable refinement of the model.

Original Insar processing by Patricia Wright, GEC Marconi Research Centre in collaboration.

Subsidence is an engineered deformation. The objectives are to optimise mine productivity whilst minimising surface strain and consequent damage liability, operating within a regulatory environment. To monitor and achieve this, subsidence is typically surveyed annually and more often where necessary. Ground surveys are costly, slow and have very limited coverage. UK mines have total survey costs of around £900k/annum estimated from single mine costs of £30k/annum including the cost of modelling "area of influence" contours from the surveys, comparable to a small area of CTM . Mines have damage liability reserves in £millions that can be protected by the engineering benefits of CTM surveillance. Mine workings can thus be improved to maximise productivity and minimise liability. There is a global, cost-effective market in this area. Furthermore, many older mines often now abandoned, were not engineered to the same standards as today. Old workings have slowly decaying support pillars resulting in ongoing and unpredictable subsidence events. CTM can detect the long term dynamics of these areas, yielding deformation rates and early warning of significant subsidence. Mining companies have expressed strong interest in the CTM service. The anticipated release of CTM software will later enable in house image processing by mine engineers. EnviroScience - Information and Contact details

Welkom Gold Mine - South Africa

Deformation detected at the Welkom Gold mine South Africa caused by a rock burst at aproximately 2.5 km depth. This caused a seismic event of 5.6 Richter recorded by the US Geological Survey. Major faults shown in black. Image processing - Gavin Doyle - Radar Remote Sensing Group - University of Cape Town.

North York Moors - Mining Subsidence

InSAR Image of mining subsidence (red/orange/yellow feature) detected in North Yorkshire. The deformation field here is interpolated from sparse coherent data.

Silesian Coalfield Czech Republic.

Collaboration with VSB Technical University, Ostrava, CZ has resulted in first subsidence images of the Ostrava Karvina district of the Silesian Coalfield. Mining here is by the caving technique and results in widespread ongoing subsidence, of less regular profile than experienced in the UK. The images below are the interferogram and height change maps for a period of 35 days in 1993. Numerous areas are being worked at this time. Subsidence is up to 30 mm.

Above - Interferogram of 35 day subsidence, Ostrava Karvina District, Silesian Coalfield

Right - Unwrapped height change from the above interferogram. 30 mm subsidence detected.

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