Super-customised Mack Metroliner ticks the right boxes

In looking for a concrete agitator specifically designed for the most extreme underground conditions, Hanson found a solution in the form of a highly customised Mack Metroliner.

About 30 minutes north-east of Bendigo in Victoria is the Fosterville Gold Mine – a completely underground mine that runs 24/7, all year round.

To prevent the mine shafts collapsing, miners spray high-density, rapid-drying shotcrete onto the walls and ceiling. It’s a great solution to an age-old problem, but the question was in how to get the concrete down there.

Hanson’s concrete plant manager, Matthew Bray, was handed this problem when the company first started negotiating for the contract. He knew from the start that conditions in the mine are extreme, and that any truck going down there needed to be tough enough to handle it.

“It’s a harsh, incredibly dusty environment that often turns to mud and slurry the moment it is exposed to water from the water carts or mining machines,” Bray said. “The temperature down the bottom can get up to 50°C. Truck filters clog up quickly which compound into a vast array of truck faults.”

That’s where Hanson’s super-customised Mack Metroliner comes in. The three new Metroliners are expected to enter service within a month or so and will work around the clock.

“We’ve got 13 drivers doing 12-hour days, seven days a week, with a week off, then the same schedule at night,” said Bray. “We’ve got the Guardian system installed to keep an eye on the drivers, and it vibrates the seat if it detects any signs of fatigue. The trucks never stop, they do two or more trips each per shift, and it’s a three-hour round trip down and back. We service them every 400 hours, and we change every filter every time.”

Hanson installed all the heavy-duty fittings on the Metroliners, including extra layers of paint and rust-proofing, large custom external trays and a single conveyor guard over the drive wheels with additional bracing to handle the bumpy and steep conditions.

“We go through about ten tyres a month so the single guard will give us more room to change the tyres out. The single guard allows us to mount larger external trays on top, which hold the chutes and some custom wheel chocks we’ve had manufactured,” Bray explained.

“When the floor is underwater, conventional chocks can float away, and if we’re on an extreme gradient they can slip. Having these handy around the truck gives us a bit of reassurance and prevents the truck sliding.”

Bray and his team worked closely with Mack engineers to customise all aspects of the Metroliners, using an agile development process that saw them making changes on the fly as new truck data came to hand from the mine. A good example is keeping the trucks slow enough to stay in control.

“The track is a steep and narrow tunnel that reaches a 7-to-1 gradient in places. Slowing the truck down enough on the descent is a major safety issue, especially when the roads are wet. If the driver sits on the airbrakes all the way down, the compressor can’t keep up and you risk running out of air and not being able to stop. Besides the obvious potential damage caused to the truck, sliding into the tunnel wall could also cause large safety and structural concerns, so this was a large challenge we worked with Mack to engineer out,” said Bray.

To get around this, Hanson imposed a speed limiter of 30 km/h on the engine, installed a transmission retarder to reduce the need for braking, and lowered the diff ratio so the retarder cuts in earlier than usual at low speeds.

“Ideally, we want the drivers to be able to get down there without using the brakes much at all. The retarder is crucial to that, it’s the way we’re expecting to control the descent, especially when the roads are slippery. The drivers are super-excited about it, they’ve had the experience of hubs overheating from riding the brakes and the seals blowing, and we’re confident this approach will solve that.”

In the confined space of the tunnels there’s very little room, so Hanson went with a single-steer model Metroliner and added a four-way camera system so the driver can see all around the vehicle.

“We also added rollover protection on the top just in case,” said Bray. “We had to modify that so it was fully-enclosed and remove all the bolts along the top to make it smooth – we wouldn’t be popular if we ripped the air ventilator bags along the roof of the tunnel.”

Designing and engineering trucks locally in Australia allows Mack to create fully customised trucks for unique tasks. “Pushing the boundaries to drive application excellence is a very strong pillar of the brand and something we’re very proud of,” said vice president of Mack Trucks, Tom Chapman.

“Partnering with Hanson to trailblaze safety and technology advances for the Fosterville Gold Mine project is a great example of this. It’s a real testament to what can be achieved with a strong business partnership where there is a commitment to mutual progress and success.”

Bray says the plan is to run the three new Metroliners for at least five years. “Mack driver trainers are coming down to help our drivers get the most out of them. It’s a complete package, and Mack really pulled out all the stops to build exactly what we were after,” he said.

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