by P A Cowsill, Peter Cowsill, K S Watts, Building Research Establishment. This paper was first published in GE’s July 2012 issue.
Large-scale open-cast mining has resulted in substantial depths of fills. Many former open-cast sites are close to centres of population where building developments are increasingly proposed. The major hazard to buildings on fill is typically associated with long-term movement within the fill due to volume change rather than inadequate bearing capacity. For mining backfill, causes of volume change are typically
- collapse settlement on inundation or percolation;
- changes in effective stress caused by weight of overlying fill;
- changes in effective stress caused by a rise or fall in ground water level;
- changes in effective stress caused by the weight of structures built on the fill.