The significant infrastructure project took many months of planning and involved drilling two new 3.5 metre diameter shafts a fresh air intake and a return air shaft - from the surface 335 metres underground to provide an additional ventilation capacity at George Fisher.

Ventilation is a critical control in Glencore's underground mines with fresh air constantly being circulated throughout the mine to ensure workers safety.

This project was needed to provide additional ventilation capacity and allow for the safe extraction of a mining block affectionately known as 'the blob' due to the unique shape of the orebody.

Senior Project Engineer at George Fisher Mine, Robert Harrington, said the project wasn't without its challenges and along the way some innovative engineering solutions needed to be developed.

"We encountered around 15 metres of ground that wasn't self-supporting on the return air shaft so we came up with the idea to use a secant pile wall to stabilise and support the ground," Mr Harrington said.

"In 10 days we installed 18 concrete piles down 15 metres which used 450 cubic metres of concrete. The pile wall was capped with a 100 square metre slab to support the raise borer.

"I believe this was the first time this civil engineering technique has been used in Mount Isa.

"All up the civil works for the fan installation involved the pouring of over 1,000 cubic metres of structural concrete."

The two shafts were drilled using conventional raise boring. This is a mining technique whereby a small pilot hole is drilled down into a void or chamber underground and then a large diameter reamer is attached which opens the shaft to its final diameter by cutting as it is lifted back to the top of the hole.

Mr Harrington said raised boring was an efficient way to create vertical openings with the two 335 metre deep shafts installed in less than four months.

"Reaming rates achieved through softer ground near the surface were fantastic and we achieved a maximum reaming rate of 31 metres in a 24 hour period which is quite amazing," he said.

Once completed, the two shafts were lined with remotely sprayed shotcrete to ensure they remain stable for the life of the mine.

Installation and commissioning of the electrical works and the fan took six weeks to complete and the fan was commissioned in March 2020.

"The fan structure is quite massive. With a 4.5 metre diameter impeller and total height of 17 metres the fan pumps over 200 cubic metres of air per second," Mr Harrington said.

"The ducting for the fan was manufactured in Vietnam, the impeller was manufactured in Melbourne, the motor and variable speed drive came from Germany with the majority of the installation undertaken by local labour."

One of the major challenges in successfully delivering the project Mr Harrington said was the integration of five major contracts which ran concurrently.

"We had to bring together and manage the project across five disciplines mechanical, electrical, civil, raise boring and shaft lining," he said.

"Managing the interface between the different disciplines was critical to ensuring we delivered the project safely and in accordance with the baseline schedule.

"It was a great collaborative effort and I'm really proud of the team as it was a huge effort over the nine months of the project."

Disclaimer: This article was first published on Mount Isa Mines newsletter, Resourceful.

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