Mack will supply three customised Metroliners for Australian aggregate company Hanson, which are designed to tackle the tough conditions at the underground Fosterville Gold Mine in Victoria.

To prevent the mine shafts collapsing, miners spray high-density, rapid-drying shotcrete onto the walls and ceiling. The extreme conditions of the mine mean any truck going down there needs 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,” said Hanson’s Concrete Plant Manager, Matthew Bray.

“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.”

Hanson installed all 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,” said Bray.

“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. 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.”

Mack engineers worked closely with Hanson to customise all aspects of the Metroliners, using an agile development process that saw changes made 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,” said Bray. “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 air-brakes 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.”

To get around this problem, Hanson imposed a speed limiter of 30kph 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.

In the confined space of the tunnels there’s very little room to traverse, 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.

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,” he said. “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.”

The three new Metroliners are expected to enter service within a month or so and will run continuously 24/7.