George Fisher raises the bar for ventilation

Specialist raiseboring works at George Fisher Mine are ensuring the continuation of safe operations as it advances its long-term mining plan.

George Fisher Mine is carrying out two simultaneous raiseboring projects to boost ventilation capacity underground and sustain the southern blocks of its L72 mining operations.

The works will see the addition of a new fresh air intake and return air shaft, both stretching 750 metres from the surface to underground and each with a diameter of five metres.

Raiseboring is used to excavate a circular hole between two-levels of an underground mine, without the use of explosives. It is most commonly used for ventilation shafts from the surface to underground, but other applications include pilot hole reaming for shaft sinking, escape rises, ore passes and borehole hoisting.

Senior Project Engineer, Robert Harrington, says two different contractors, Pybar and RUC, have been engaged to carry out the surface raiseboring works concurrently.

“We reviewed our options and running two raiseboring contractors meant we had access to more specialised equipment. This will save about 18 months on the project schedule and provides the best overall return on investment,” Robert says.

Prior to commencing raiseboring, the team completed 90 metres of ground improvements.

“The design for the ground improvements was technically challenging, but the execution phase allowed us to increase the diameter of the planned raises and completely eliminated the need for an additional fresh air intake in the long term,” Robert says.

Drilling conditions within the upper stratum of the shaft have also provided another challenge due to water loss.

“The upper geology has less strength and is more fractured compared with the shale typically encountered in the ore body.” Rob says.

“Because raiseboring uses a rotary mud drilling process, with water injection playing a critical role, water is sometimes lost through fractures resulting in delays.”

Resolving this issue typically involves grouting the pilot hole. However, the team has had mixed success with this to date, with the grouting only being successful on the return air shaft pilot hole.

George Fisher Mine Manager, Rebecca Roper, has acknowledged the tremendous amount of work the Mining Operations, Assets and Engineering and Technical Services teams have put into executing the significant infrastructure project.

“Robert Harrington has driven this project from the very start, and his dedication to ensuring its success is highly commended. It’s an excellent display of our workplace values.”

“Additional ventilation is required to ensure continued safe mining extraction as we advance into new areas of the L72 underground footprint in line with our long-term mining plan,” Rebecca says.

The new rises will be reamed to five metres in diameter and lined with shotcrete to assist with the stability.

Once complete, further surface works will take place. A cone will be installed over the fresh air intake to direct fresh air down to the active underground headings, while fans will be added to the return air shaft to facilitate the exhaust of contaminated air from underground.

Once complete, further surface works will take place. A cone will be installed over the fresh air intake to direct fresh air down to the active underground headings, while fans will be added to the return air shaft to facilitate the exhaust of contaminated air from underground.

With early works having started last May, the raiseboring is expected to be completed by June.

The second phase is due to be completed in the third quarter with the commissioning of the fans and other surface infrastructure, and the final phase is scheduled for early 2023.

In the final stage, there will be further drilling to connect the base of the surface shaft (12-level) with the base of the mine (18-level).