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1 School of Environment & Development, Sheffield Hallam University, Sheffield S1 1WB, UK m.oneill{at}shu.ac.uk
2 Department of Civil & Structural Engineering, University of Sheffield, Sheffield S1 3JD, UK
The material used in the restoration of opencast coal mines is made up predominantly of mudstone particles ranging in size from less than 60 µm to more than 60 mm nominal diameter. Post-compaction settlements are mainly sub-divided into short-term ‘collapse’ and long term ‘creep’ components, both of which can be very large and often significantly reduce the development potential of restored opencast sites. As the mechanics of these movements are poorly understood at present, X-ray computed tomography (CT) was used to investigate the fundamental nature of particulate interactions within specimens of backfill undergoing long-term creep settlement.
The preliminary results from a series of CT analyses of a number of large scale specimens are presented. Different CT procedures were used and an indication for best practice for scanning of large samples has been found. Qualitative interpretation of the images obtained to date is presented in terms of fill structure, particulate changes during settlement and effects of arching. Indications are that particle breakage is a less significant mechanism than previously thought, and that local collapse of voids, particle sliding and particle rotation are the dominant mechanisms. Quantitative data to be extracted from the images may lead to a probabilistic approach to the prediction of settlement. This possibility is noted, as is the potential for the wider use of CT in geotechnical engineering.
