The report from Victoria’s Department of Primary Industries referenced government investigations which established the batter failure was caused by block sliding, triggered by water pressures in a joint along the rear of the collapsed batter area and by water pressures in the interseam clays underlying the coal.
“The warden found that there was a failure of the geotechnical management system at all levels and the future significance of many important signs evident prior to the collapse – that showed that failure was imminent – were not interpreted correctly and were not recognised either internally or externally by technical advisers and reviewers,” the DPI said in the draft significant incident report.
The DPI consequently recommended mine operators to ensure hazards associated with batter collapse have been identified, a risk assessment has been undertaken and necessary risk controls have been implemented.
“The stability of batters must be maintained by the use of appropriate control measures resulting from the full integration of geology, hydrogeology and soil mechanics into geotechnical stability models,” the department said.
Mine operators were also advised to continuously develop their geotechnical and hydrogeological models.
“It is critical for maintenance of future stability in mining operations that the historical experience and understanding is not lost, but effectively captured in new and evolving models of understanding,” DPI said.
In-field monitoring of the batters was recommended to be used to confirm mine stability modelling and assessments with such work to be undertaken by suitably qualified persons and checked by peer review.
“Mine operators must ensure any new or significant changes to mine plans, mine layouts or mining systems are suitably evaluated from a geotechnical and hydrogeological basis before they are adopted,” the department said.
The 2007 incident at the Yallourn mine, which fuels a nearby coal-fired power plant, caused major damage, including to conveyor systems and the environment.
Further information is available from the Victorian DPI’s website.
