The original repair process included the re-opening of the Hart Shaft to remove the blockage caused by a failure 47 metres below the surface and the installation of a plug in a deeper, more stable section of the shaft.

West Tamar Council general manager Rolph Vos said the latest information received meant it was too dangerous to move forward with the initial plan.

“The risk associated with entering the shaft is too great and it is just not safe to have personnel within the shaft, and our previous plan to have people go down the shaft to fill it [won’t work],” he said.

“We now have to look at external stabilisation.”

This will include drilling down the outside of the shaft, and pumping high-pressure grout into the hole which would fill the cavities around the failures and damage.

“It will be a series of holes that will form a barrier, like a series of poles that will form a ring around the shaft,” Mr Vos said.

“[Engineers at Pitt and Sherry] are working on the practicalities and the costs of doing that and I believe we will have information on that next week.”

Exact details on whether this process will incur further costs on top of the estimated $1.25 million repair bill is not yet known, but Mr Vos said he hoped the reduction in remediation work would balance the amount.

The funding will be shared between the West Tamar Council and the state and federal governments.

“It becomes a geotechnical discussion rather than just mining because it’s about ground conditions as much as it is about remediation,” Mr Vos said.

A cable stay is also being attached to the iconic headframe to prevent further movement. “It’s primarily to improve the safety of the site because the weight of that, combined with the ground movement, puts pressure on the concrete slabs and the surrounding area,” he said.