Drill and blast innovation on display at Roy Hill mine project

The size, scale, and remoteness of the massive Roy Hill iron ore mine has created a raft of hurdles in developing the operation.

The $10 billion project requires mine, rail, and port infrastructure, with such a ramp up that construction already sits at 60 per cent , as it seeks to hit its massive 55 million tonnes per annum production rate.

However these hurdles and high targets have seen contractors and workers on site approach these issues in unique and innovative ways.

One contractor, Action Drill and Blast (ADB), has been carrying out drill and blast work at the site, and used an innovative hybrid explosive technology to overcome the project’s challenging ground and logistical conditions.

In December 2013, ADB was awarded the contract for drill and blast works covering over 170 kilometres of rail cuttings (which increased to 220km during the course of the contract) for the Roy Hill rail track by mining and civil contractor, NRW.

NRW is sub-contracted to Roy Hill’s EPC Samsung C&T for the Roy Hill rail earthworks, whilst ADB is a wholly owned subsidiary of NRW Holdings.

The ADB project itself required a team of 65 personnel operating eight drill rigs – a mix of Atlas Copco F9C and Atlas Copco D65 drills and associated ancillary equipment to drill and blast approximately 2.4 million cubic metres (bcm) of in situ rock for a large portion of the 344 kilometre long rail track which is being constructed from the mine site, located north of Newman, to Port Hedland.

However it was not completely straightforward, with ADB encountering several operational challenges on site, including very wet ground conditions: heavy rainfall resulted in significant levels of ground water and closed parts of the site for length periods; logistical challenges: poor roads and the wide spread nature of the site made equipment and personnel mobilisation time consuming and negated off-site explosive storage as an option; and communications challenges: the lack of radio and phone coverage due to the remote location meant  special systems were needed  to manage interactions between staff and other mine infrastructure owners.

To overcome these wide ranging issues, ADB used ‘hybrid’ explosive technology WALA during the process.

“The company highlighted the cost benefits of its in-house supply capability, the ability to store the product on-site, and its suitability for use in both wet and dry ground conditions and the availability of variable density bulk explosive product,” ADB stated.

“These advantages proved even more critical to project delivery given the quantity of water encountered – far more than has been historically seen on these types of projects – and the logistical challenges.”

Most projects use ANFO explosive mixes as they are cost effective and relatively easy to store.

However it has major downsides, because unlike WALA it is not suitable for use in wet ground as water mixed with ANFO creates toxic nitrogen dioxide gas.

“WALA is a new generation of bulk explosives. Unlike the conventional emulsion and watergel bulk explosives, WALA employs a cutting edge technology called NanoBlok. This enables WALA to achieve very light densities – as low as 0.7 grams per centimetre cubed (g/cc) – while maintaining water resistance and initiation sensitivity,” ADB explained.

The mix also has more effective energy strength, and is considered a quadruple salt bulk explosive.

The single salt ANE formulation ADB used to compare the WALA to ANE is the standard formulation used by some of the ANE suppliers in WA.

Some of these suppliers have a water content of up to 22 per cent.

The WALA formulation which was used for the trial in a Queensland mining operation and at Roy Hill Rail Project has a water content of 10.22 per cent.

The combination of high VOD (the speed it detonates at), greater sensitivity at lower densities in smaller diameter holes and high detonation temperature/pressure creates unique characteristics in blasting performance.

Its NanoBlok characteristics also enable WALA to tolerate a longer sleeping period in the presence of water and to soft ground conditions without producing post blast fuming.

Smaller holes and wider patterns were used on WALA patterns comparing to ANFO.

This meant drilling fewer holes in hard wet ground and was a huge cost saving measure on the project.

Where ANFO can only be augered / poured into blast holes WALA was pumped at low densities through small diameter hoses on tight patterns, uneven ground, split benches and difficult to reach blast holes that ANFO would have been manually handled in buckets to the blast holes. WALA can also be pumped as far as 60m away from the MPU.

As a rule of thumb ADB design engineers estimated WALA’s bulk effective energy strength to be at least 15 per cent higher than comparable emulsion bulk products when calculating blast designs on the Roy Hill rail project.

Through a combination of these factors of WALA ADB was able to overcome the inherent logistical issues found at Roy Hill.

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