A clean break

The Sandvik DB120 drill rig. Splitting oversized boulders in an underground mine can be dangerous and can slow down production. A new drill rig with remote control and a hydraulic splitter makes secondary breaking safer and faster.

Published: 7 March 2012

As the dust settles in the drift after the latest blast, a problem appears. A boulder measuring two metres by two metres sits firmly on the ground, blocking any further access to the ore. The underground loaders must wait while the foreman considers the options, and production in this part of the mine is brought to a halt. Traditionally, handling a situation like this requires somebody to approach the boulder, drill holes in it, charge them with explosives and blast the problem away. Typically occurring in hard-rock mining like block caving, sub-level caving and stoping, this can be a dangerous task.

“These mining methods create boulders in positions where there is a risk of getting injured, or even killed,” says Sami Järventausta, engineering manager at Sandvik.

That was one reason why Järventausta and his colleagues were tasked with giving miners a new option. Another reason was to reduce downtime caused by blasting and the subsequent evacuation of dangerous fumes from the explosion. This procedure will sometimes block access to the ore for one or more shifts, causing a substantial drop in productivity. The same goes for alternative methods such as pulling the rock out of the way to break it in a more convenient place.

No boulder too large

Pybar Mining Services in Australia is the first mining company to deploy the Sandvik DB120 in commercial operation. This is a new remote-controlled underground drill rig for secondary breaking of oversized boulders using the drill-split method.

“We send it out into the open stope so we can break down the oversize rocks, to enable them to be moved away from there in more manageable sizes,” saysBrad Watson, Pybar’s project manager at Tritton Copper Mine, where the company is contracted to carry out the underground mining. “Then we can continue to bog the stope out by remote.”

Pybar is a 900-employee mining and civil construction company based in New South Wales, contracted for mining operations across Australia. The underground mining at the Tritton Mine has been carried out by Pybar since 2008. In 2009 the mine produced more than 24,000 tonnes of copper. The Tritton Copper Mine is owned by Straits Resources.

Brad Watson and his crew of 80 often have to break boulders that block the draw points or are too big for the loaders. Before the arrival of the drill rig, the main alternative was to use explosives. But with a risk of sulphide dust ignition due to the properties of the ore, this could only be done between two shifts when there were no people in the mine.

“If the rock came down early we would have to wait the whole shift before we were able to fire it and get back to drawing the ore,” Watson says.

Now it will only take a couple of hours after a boulder has been identified to be back in production again.

The result of the design team’s engineering efforts is the Sandvik DB120, an underground drill rig specially designed for secondary breaking. Using radio remote control and the drill-split method, it makes it possible to break low-lying draw-point blockages into smaller pieces from a safe distance without using explosives. The operator controls the process with a hand-held control panel that can be fitted with an integrated video screen as an optional extra.

Based on an existing surface drillrig model, the DB120 features a wheel end and a boom on which a hydraulic drilling module with a splitter is fitted. The splitter has been specially developed for this application. Splitting can be done in many different ways, and Sandvik’sengineers have tried to spread the force more effectively than other types on the market.

“What is truly new in this machine is the splitter feed and how it uses the drill hole to split the boulder,” says Ulla Korsman, product line managerat Sandvik.

When the drill has done its part, the rig’s mechanical index system will position the splitter exactly above the drill hole without moving the boom. Then the splitter is inserted into the hole and the hydraulics push a wedge-shaped spline forward, expanding two outer splines until the boulder breaks into two pieces. It’s fast and relatively quiet, and the dust levels are low. Usage is not limited to a certain size of boulder. Bigger ones can be split in suitable pieces step by step in a time-efficient manner.

The entire unit is powered by an on-board diesel-hydraulic system that makes it completely self contained. With a weight of 5.6 tonnes and fit for a drift size of three by three metres, it all adds up to a compact and agile machine that is easy to get into position.

“Once it has been identified, you can have the rock gone in two hours,”
says Brad Watson, project manager at Pybar Mining & Civil Contractors, the contract operator of the Tritton Copper Mine, 65 kilometres west of Nyngan, Australia.

Tritton is an open-stope mine that once required a 12-hour shift or more to remove a boulder that was blocking a draw point. In May 2010 Pybar tested the drill rig in commercial operation for the first time, and after evaluation it decided to buy the unit (see sidebar). From a maintenance point of view the machine is no different from an ordinary drill rig, except that the splines in the hydraulic splitter will eventually wear out and will need to be replaced.

“Our tests show that in normal use they don’t have to be changed so often,” says Sandvik’s Järventausta. “There is an automatic greasing system that will extend their lifetime.”

Another feature worth mentioning in terms of maintenance is the 12-volt electrical system, which is easier to deal with than those with higher voltages.

The DB120 drill rig
Ready to rock
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A soft path through hard rock