18 May 2017
Landslides that make you gasp Part 1: Yallourn
I thought it would be fun to do an occasional series on landslides that make you gasp – i.e. those that cause genuine surprise – and a first good example is the Yallourn landslide. This one happened at the Yallourn Coal Mine in November 2007. I had never seen one quite like this before, and indeed since:
This remarkable landslide is described in an article from the time in the Herald Sun:
A HUGE landslide at one of Victoria’s biggest power plants – Yallourn power station – has slashed electricity production. The landslide has left Yallourn running at less than a third of its capacity ahead of a week of forecast 30C days.
The slide appears to be a deep-seated rotational failure. An investigation after the event led to a report in the Sydney Morning Herald about the landslide:
A HUGE mine collapse that crippled a vital Latrobe Valley power station was caused by slack and lapsed safety precautions, a report has revealed. Mine consultants had lacked the skill to give competent advice for more than a decade, according to the official investigation into the spectacular Yallourn mine failure in late 2007. And the State Government-appointed investigator, Tim Sullivan, found evidence that the Latrobe Valley’s brown coal mines and the massive pumping of groundwater associated with them could be causing earth shifts outside the mines’ boundaries that posed a risk to nearby dams and roads. This finding has prompted the Government to establish a valley-wide review of the region’s stability.
In his report recently tabled in Parliament, Mr Sullivan said the expert consultants failed to pick up obvious signs of the mine’s imminent failure. The day before the collapse, large cracks appeared on the road on top of the wall, a pipe and line of power poles along the wall had begun to curve and large amounts of water were gushing into the mine at 500 litres a second. Despite this, the consultants concluded that “catastrophic failure was unlikely”. But Mr Sullivan, who also reported on the 1997 Thredbo landslide, said the problem went back many years to when experts approved the cancellation of two fundamental mine safety measures in the name of “efficiency”.
It is common practice in the Latrobe Valley to relieve the build-up of groundwater by drilling horizontal bores and pumping water out of deep aquifers. If this is not done, water builds in the coal seam and the wall shifts in what is called “block sliding”. But in 2002, on consultant’s advice, the mine stopped drilling horizontal bores and, in 2004, stopped taking water from the deep aquifer below the floor of the mine. Mr Sullivan found that “somehow the historic understanding and knowledge became lost or was no longer properly appreciated”.