Mine subsidence caused by current and past mining activities is a serious environmental and safety hazards as it can damage rivers, cliffs, power lines, pipelines, communication cables, major roads, bridges, buildings and much more. Subsidence control technology based on fly ash backfill has major advantages because it not only reduces the risk of surface subsidence, but also helps dispose of waste material underground. Since 2002, CSIRO has been developing effective and economical technologies both for subsidence reduction of longwall mining and remediation of abandoned bord-pillar mines.

Overburden grout injection technology

Overburden grout injection is a technology used to control coal mine subsidence by injecting waste material (e.g. flyash or coal washery waste) into the overburden during longwall mining. This technology has a potential of reducing mine subsidence by more than 60%.

A schematic drawing of the overburden injection technology to control mining induced subsidence

Mine remediation technology

Many old abandoned bord-pillar mines exist in Australia’s urban areas. Two subsidence events occurred in such an area in Collingwood Park, Ipswich. With support from the Department of Natural Resources and Mines (DNRM), CSIRO developed a cost-effective non-cohesive backfilling technology for remediation of the abandoned mines, and carried out a detailed assessment of the effectiveness of non-cohesive backfill both by numerical methods and laboratory simulation.

A numerical model to investigate the effect of non-cohesive backfill on pillar strength.