Published in June 2007 Australian Longwall Magazine
The New South Wales-based company is currently in the final stages of refinement and testing of its SDRB system. Already field trials have shown bolt installation cycle times using the new SDRB are less than half the installation cycle times of conventional bolts.
While the improved development rates achieved from using SDRBs will vary with every mine, it is possible that the new SDRB will remove bolting as the major factor limiting roadway driveage rates.
From a big picture perspective, the self drilling rock bolt will be an essential component of increasing roadway development rates and fulfilling the industry’s aim of a 15 million tonne per annum longwall.
A survey of participants at the March 2007 ACARP Roadway Development workshops showed speed and ease of operation of bolting rigs as the second-largest barrier to improved roadway development rates at Australian longwall mines. Solutions proffered by participants included development of a SDRB.
SDRBs that use cement grout to anchor the bolt have been around for many years in the civil and tunnelling industries, however they are not suitable for the coal industry, which requires immediate roof support at the working face.
With this in mind, Ground Support Services has set about developing a full column resin encapsulation SDRB with its partners Alminco and 545 Global, specifically for the coal industry.
This new SDRB comprises of a thick-walled hollow steel bar with a drill bit on the end, enabling it to drill its own hole in a conventional manner. Once the hole is drilled, water and rotation are turned off, and then resin is pumped into the bolt and back down the outside annulus of the bolt until it is fully encapsulated with resin.
As the resin is being pumped through the bolt, it is already starting to cure, setting only a few seconds or so after the bolt is fully encapsulated with resin. Once the bolt is full of resin and is set, the nut is then tightened up against the bearing plate, and the drill chuck can be lowered from the roof, ready to install the next bolt.
Trials have shown a 2m SDRB can be fully installed in 60 seconds including drilling, full column resin encapsulation and nut tensioning.
“This new SDRB system is unique in that it uses full column, pumpable resin such that it not only provides high load transfer capacity right down to the borehole collar, but also enables voids and cavities in broken or highly stressed roof to be filled,” Ground Support Services’ Peter Gray said.
The most obvious advantage of the new SDRB system is the removal of so many manual steps in the bolting process. The only manual process with the new SDRB is for the operator to pick up the bolt and put it into the drill chuck. Gray said ultimately automation could be used to pick up the bolts and place them in the chuck, via a carousel or similar system.
Practical advantages of the new SDRB system include faster bolting cycle times; less manual handling on the miner; less operator injuries; higher quality bolt installation which includes perfect resin mixing, full encapsulation, less bolt corrosion, and may translate into better roof support and possibly a reduction in bolt density, and or less secondary support.
“Although the consumable costs of the SDRB itself are obviously higher than for a conventional rock bolt, the labour and capital costs of operating a continuous miner unit at the face are very high, and this new SDRB system enables much higher productivity of this expensive continuous miner unit. This will result in greater roadway driveage rates,” he said.
It hasn’t been all easy riding for Ground Support Services’ development of the SDRB system, as the company has been determined not to compromise on its original vision.
“We have not taken the easy or convenient approach to design of an SDRB system, but rather have set out an initial set of design criteria and stuck to them despite having to overcome considerable problems.
"For example, the SDRB is a system not just a bolt, and with our partners Alminco, we developed the pumpable resin system even though there were much simpler bolt anchoring solutions available, but pumpable resin provides the best and most effective rock bolt anchoring system for the coal industry,” Gray said.
The next step is to put the SDRB system onto a production machine.
To fit the system onto existing continuous miners, Ground Support Services and Alminco face various challenges: current machines are not designed for SDRB; there is little space available for bolting or consumables; and there are concerns on where to place the resin tank. The solution is to use good engineering design to be able to retro-fit existing continuous miners and in the longer term, design the miners with SDRBs in mind.
Of course, higher roadway driveage rates require higher levels of consumables, which create the vicious circle of where to store consumables and how to re-supply consumables to the miner. Gray said the solution was in a re-design of the miner bolt cassette system and a re-think of how consumables are re-supplied to the miner.
