SETTLEMENT OF OPENCAST COAL MINING BACKFILL AT HORSLEY 1973-1992

A 70 m deep mudstone and sandstone opencast coal mining backfill at Horsley near Newcastle has been monitored throughout a 20 year period from 1973 to 1992 during which the ground surface has settled by as much as 0.8 m. A 34 m rise in ground water level between 1974 and 1977 has been a principal cause of the settlement. Settlement at depth within the fill has been measured using magnet extensometers and surface movements have been measured by precise levelling. The implications of the ground movements for building developments on opencast backfills are briefly discussed. (A) For the covering abstract see IRRD 859718.