Work has begun to plug the ventilation shaft at the former Pike River mine ahead of the planned re-entry, Solid Energy says.
The company announced this afternoon a high-strength expanding resin had been placed into the mine shaft, which had then been topped with concrete.
``Once the concrete has set, the remaining area will be filled with an expanding foam material which will also be topped off with a final layer of concrete,'' the company said in a statement.
Sealing the shaft is designed to ``fully stabilise the environment in the mine''.
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Solid Energy said the bottom 40 to 50 metres of the shaft, originally about 100 metres deep, was filled with rock from an earlier collapse.
The remaining area, which is being filled in this phase of the re-entry project, is approximately 700 cubic metres in volume.
After the ventilation shaft is sealed off completely, the mine would be pumped full of nitrogen to force out any methane gas and allow experts to walk down a 2.3km shaft to a rockfall.
Solid Energy also said today workers were continuing to plan for the next phase of the re-entry plan, which involved drilling additional boreholes into the main tunnel.
In September, Prime Minister John Key pledged $10 million of government support for a re-entry plan if it was safe, technically feasible and financially credible.
The majority of the 29 men who perished in the November 2010 explosions were believed to have been inside the mine's main workings at the time, but their families believe some may have been inside the drift when the blasts occurred.