The examination and prediction of opencast backfill settlement
With ever increasing demands on land use large areas of land are being considered for development which due to past or present mining activities are covered by substantial depths of fill materials. The problem faced with the development of land infilled with open cast mining backfill is in predicting the behaviour of the fill upon development. To be able to design foundations suitable to withstand the movements that occur within opencast backfill or design a backfilling operation that produces land suitable for a proposed after development, a means of predicting backfill settlement is required. From the analysis of a considerable quantity of data collected from the monitoring of backfilling operations and backfill movement at a range of opencast coal sites located within the UK, the behaviour of opencast backfill has been examined and better understood. This information has enabled a method of predicting backfill settlement to be developed which has been subsequently implemented as a computer program running under the Windows operating system. Factors taken into consideration during the prediction process are the timing of backfilling operations, the compactive state of the backfill, the inundation of the backfill and the influence of surrounding material and a means of predicting differential settlement due to backfill heterogeneity is proposed. Examples are given demonstrating the significance of these factors upon settlement predictions made at a hypothetical site. Finally, a comparison is made between predicted settlements and those monitored at an actual site to demonstrate the validity of the method proposed.