Stability, safety and speed are key factors when excavating tunnels at a mine site. While road headers are a popular choice for the job, they may not use as much stable ground support required for drift excavation.
In what is a first for the Queensland coal industry, a coal mine in Central Queensland will be using a tunnel boring machine (TBM) for drift excavation.
Mining and engineering services company Redpath will be supplying the TBM for Anglo American’s Grosvenor coal mine in the Bowen Basin.
The eight metre diameter Earth Pressure Balance (EPB) TBM was manufactured by Robbins and will be used on the coal mine to excavate two drifts instead of the traditional method of using a road header.
The announcement of the new division coincided with the company’s first coal mining contract following its work on the Rio Tinto Kestrel Mine Extension project near Emerald, Queensland.
According to Redpath’s general manager of coal Gavin Ramage, TBM offers a safer, quicker and more stable excavation option.
“The tunnel boring machine is expected to excavate drifts at least three times faster than a road header, which provides much quicker access to coal,” Ramage said.
“There are also a number of safety benefits associated with using the TBM, mainly from the highly stable and durable ground support required, which has a 50 year life expectancy, as opposed to the less stable support used for a road header.”
Using the TBM removes the need to rehabilitate the drift support every 10 years as the TBM support has a life expectancy five times that which is laid for the road header.
Ramage referred to an incident Anglo American’s Moranbah North mine, where a roof collapsed over its conveyor drift in 2011.
All operations had to stop at the mine until the rubble could be cleared and the conveyor drift repaired.
Ramage said fully segmented lining will diminish the likelihood of any collapse or ground support rehabilitation or issues once the excavation’s conveyor belts are installed.
The TBM excavates and supports at the same time.
Ramage said the option to use TBM on the Grosvenor coal site was proposed in Redpath’s tender about a year and a half ago.
While the traditional excavation method of the road header was the first option, Redpath proposed the TBM as something to examine.
“The (Grosvenor) project has some poor ground conditions for the first 50 metres vertically. This was thought to be a better solution both in excavating the drifts and for long term stability,” Ramage told Australian Mining.
The ground support needed when using a TBM is akin to that of cross-city tunnels, which is stable and long-term.
Ramage said typical ground support regimes have a used-by date. The bolts and mesh system may have a lifespan of 10-15 years and once it reaches its use-by date, miners will need to rehabilitate it.
This can be expensive, disruptive, and may cause operational problems in the drifts or accesses.
With TBM, Ramage said the ground support regime is replaced with full segmental lining instead of the traditional bolts and mesh.
This means it will be a safer environment for the teams of workers who access the drift and operate the conveyor system.
It removes people away from hazardous areas during excavation on poor ground, Ramage said.
Anglo American’s Grosvenor project manager Glenn Tonkin said the company was excited to be pioneering the tunnelling method to build the five million tonne a year Grosvenor mine.
The company’s board approved its coking coal mine in December 2011. Located just south of the company’s Moranbah North coal mine, it targets the same Goonyella Middle coal seam as the Moranbah mine.
Anglo will spend approximately $US1.7 billion on the mine.
“The $40 million earth pressure balance machine is under assembly on site and will be ready to break ground next month,” Tonkin said.
“The innovative TBM tunnelling method will allow us to reach the coal seam by December this year, bringing us that step closer to longwall production in late 2016.”
Redpath is looking to start cutting and excavating the first drift at the end of October.
The longwall operation has a mine life of around 26 years.
Construction on the Grosvenor project started in July 2012. It will need more than 3,000,000 cubic metres of earthmoving and more than 13,000 cubic metres of reinforced concrete.
Redpath recently brought over the world’s most powerful raise drill to South Australia to begin work on its first job in Australia.
The raise drill was designed for underground and civil projects where underground access is available.