TASMANIA AND THE BIG BANG

At one o’clock in the afternoon some three times a month, a massive blast from nine tonnes of ANFO high explosive signals the start of a new economic cycle in Tasmania.

It is a sound – and a shiver through the bedrock of an entire region – that will put into motion scores of giant machines, hundreds of massive trucks, and of men and women the length of the state.

They, in turn, will deliver the raw material that underpins new homes and driveways, along with the shopping centres, schools and shiny new businesses that surround them, the roads and bridges that connect them.

This entire world revolves around the largest single quarry in Tasmania. It is the 50-hectare Hobart Blue Metal Industries quarry, part of Hazell Bros, itself a company with deep roots in the state.

Each of these carefully controlled explosions in the deep dolerite of Leslievale, a few kilometres southeast of Hobart, renders some 25,000 tonnes of what is commonly called bluestone.

In a single year, a million tonnes will leave here to become concrete, road base and road surface. It will form the substrate for railway lines, shape drains and become rip-rap, to bolster vulnerable earthen banks along rivers and lakes.

The detonation three times a month is the first part of a process that will see that bluestone reduced to specially calibrated and purposed gravels, most less than 20 mm across.

It is the physical and chemical properties of dolerite, an igneous rock laid down in the Jurassic era, that make it a preferred constituent for this task. Extremely hard, dolerite is quite literally construction’s core building block.

As the dust clears from the explosion at the quarry face, four huge machines begin work synchronously.

A 50-tonne Hyundai steel-tracked excavator – equipped with a giant hydraulic rock-breaker at the business end – smashes oversized rock debris into pieces smaller than a cubic metre.

The resulting boulders are then scooped up by a Komatsu loader, 12-tonne buckets-full at a time, which it dumps into a pair of Komatsu haul trucks.

In just ninety seconds, four such bucketloads have filled the truck to its 45-tonne capacity. It’s ready to get tipped into primary crusher units.

“Everything here is large-scale,” notes John Sherburd, business manager at HBMI, listing some recent invoices as an example.

A pair of new loaders is a cool million dollars; just the tyres for one of them are $56,000. Meanwhile, the quarry machinery drinks 3,500 litres of diesel every single day.

Hazell Bros, employing more than 500 staff through various business units, has a wages bill alone of $30 million a year. Then there’s over a 100 contractors with tractor-trailers, and Forze Explosives, the firm responsible for the regular detonations at the quarry.

What’s generated by this huge operation circulates through the local economy, then across Tasmania.

From a control room sited to provide a direct view of primary and secondary crusher units, a single individual can monitor the entire operation, all the way to the specifically sized outputs of gravel (called ‘aggregate’ in the trade) at the end of the production line.

Machines, even their internal workings, are watched on CCTV. Jams can be fixed using such tools as mini rock-breakers on a remotely controlled arm operating within the crusher unit itself.

This is the most sophisticated quarry operation anyway, asserts Sherburd.

When the quarry’s yield is delivered into the primary crusher, a massive steel jaw (its opening is ‘the gape’) brings to bear a force measured in kilonewtons per metre. As rock is compressed against steel, the material is reduced to pieces that are a relatively miniscule 150mm in size.

At a rate of 420 tonnes every hour, these pieces go via conveyor into a secondary crusher unit which reduces it again, this time to gravel in the desired sizes: 20, 14, 10, 7 and 5 millimetres, along with what bears the technical term, ‘dust.’

These final screened products are then stockpiled for sale.

Sherburd explains that crushers actually shape the gravel. “Elongated pieces don’t have the desired strength” he says. “Size is also key, as gravel is recombined in various formulations to suit its end use. For concrete, it must be very clean (no dust) and carefully sized.”

This stuff also matters in road building, he adds. “For instance, FCR (fine crushed rock) goes down just before the layers of asphalt on highways, so it’s critical that it forms a solid road bed.” Forty nine percent of quality FCR is actually rock dust.

“None of this is just rock,” points out the man who can tell you the specific gravity of his raw material.

Large quantities get loaded into what the trade calls ‘ten-yarders,’ 47 tonnes at a time in a truck-and-tailer unit. Every day can see 3,000 tonnes of gravel go over the HBMI weighbridge in up to 300 of these units.

The HBMI quarry itself is on a 790 ha. lease, but its footprint and associated buildings barely cover 50 hectares. There’s enough solid rock here for 50 years and well beyond.

Aside from the explosions, the quarry operation and its associated crushers are surprisingly quiet.

Dust, a scourge, is kept to a minimum. Quarry faces are clean, and its vast floor is kept clear. “Even visually, the quarry makes no impact on the broader environment,” notes Sherburd. The Huon Highway is over a kilometre away and screened from operations by thick bush.

To keep the environment clean, the quarry’s secondary crushing plant – actually three crushers in series – is now housed in a single building, with the effect of significantly cutting the quarry’s dust output.

A ‘bag room’ and technologies attached to the conveyor belts also keep the dust down.

At the forefront of Sherburd’s mind today is a series of upcoming projects. He’s weighing the size and site of the work, considering competitor companies like Boral, how the quarry output might dovetail with actual construction, which is another division of Hazells.

Tasmania’s highway projects, for example, have become massive: 2011’s Kingston Bypass (which drew huge tonnages from nearby HBMI) was a $60 million project, but in 2014 those numbers were dwarfed by the Brighton Bypass at $164 million.

The current ten-year plan to upgrade the Midland Highway has upped the ante to $500 million. Quarried gravel represents a substantial part of those millions.

His company has positioned itself for this growth, with large quarries at Breadalbane, at the north end of the Midland Highway and at Long Hill, off the Bass Highway between Devonport and Deloraine. Dolerite is exposed over half of Tasmania.

The thinking here is simple, says Sherburd. “Transport is expensive, particularly the cost of diesel fuel, so proximity to a work site is a crucial issue for any large project.”

This fundamental is well understood around the Leslievale quarry.

Some 40 years ago, Don Hazell – then the company’s prime mover – learned a privately owned quarry at Lenah Valley did not have the gravel needed to fill his orders, or his trucks.

He solved the problem in typically gutsy fashion, and opened his own at Leslievale.

The timing turned out to be serendipitous, as the Southern Outlet, a long-needed highway to replace the tortuous two-lane road to Huonville, traversed the terrain right past Hazell’s quarry site.

In the quarry business, size matters. But distance from the job is a very close second.