Underground » Roadway Development
ACIRL was commissioned by the Roadway Development Taskforce of ACARP to examine a relatively new device called a mobile boot end. The objectives being to critique its performance to date at 3 mines; comment on how this device may impact on longwall development systems of the near future and review research requirements for longwall development, and particularly associated with mobile boot ends or similar devices.
The Mobile Boot End designed and built by Australian Longwall Pty Ltd has been examined in service at three mines, Ellalong, Homestead, & Oaky Creek, all of whom use it longwall gateroad development, but in slightly different ways, and/or for different reasons. It has shown it is capable of increasing the development rate in a two heading development, but by varying amounts, depending on its manner of use, and the conditions prevailing at the mine.
The Mobile Boot End, as its name suggests, is a crawler mounted boot end, which can either remain static until a belt extension is required, or alternatively, it can dynamically advance behind a continuous miner, pulling out the belt from a loop take-up supply as it goes. In this latter format it effectively is a continuous face haulage system. However, unlike other continuous haulage systems, it has only an ability to operate in a straight line. The Mobile Boot End has numerous features to enable it to traverse the spectrum of roadway profiles commonly seen, and at the same time, to enable the belt to be easily tracked.
When used with a "conventional" panel belt system, the Mobile Boot End can replace shuttle cars and their associated delays, but only for straight ahead drivage. In this configuration at Ellalong, a reduction in minutes/metre advance of 35% was seen in Longwall 10, but only 9% in the early parts of Longwall 11. More recent studies by mine in Longwall 12 gateroads have shown gains up to 28%.
At Oaky Creek Nol, the Mobile Boot End is used in conjunction with shuttle cars, and has the primary roles of speeding panel move times and simplifying the ongoing alignment of the tail end on a cross-graded floor. The result in its first panel of use was a gain in metres/worked shift of 30% (over the prior system using a Stamler feeder and fixed boot end). At present, inadequate data exists to show if all this change was solely due to the MBE introduction, and if the margin has continued into the current panels.
The Mobile Boot End has also been coupled with the Meco-McCallum Matchappel "quick set" folding conveyor system at Homestead (Wambo), and over a 3 month period, achieved a 25% improvement over a shuttle car system in a companion road. At Homestead however, the delays in advancing the Matchappel system, after each two pillars of development, have reduced the net gain to virtually zero.
The Mobile Boot End has proven exceptionally easy to move forward. In two mines, the formal survey system for alignment was quickly dispensed with in favour of visual alignment of some part of the MBE chassis with roof marks.
In most applications the Mobile Boot End has created some difficulty in moving supplies to the face, though the full impact of this will not be seen until the unit is employed in development with much higher advance rates, probably associated with a continuous cutting and bolting machine, and/or under conditions of negligible roof support delays. In all the mines, the MBE design has created some difficulties in the clean unloading of shuttle cars, and at worst, promotes car bogging at the boot end.
The Mobile Boot End has so far demonstrated it can be a practical and reliable device. The industry now has to decide how best it can be applied. In a longwall gate road environment the next obvious challenge will be to match it with a reliable mining machine which has the ability to simultaneously cut and bolt. For such a match to be successful, the question of how (if at all ) to drive cross-cuts must be addressed. Also, the difficulties in continually advancing and reloading the Matchappel system must be solved in a practical manner if this device is to gain wide acceptance. Alternatively, more easily handled, conventional design structure is needed, and this can be advanced one bay at a time behind the MBE, and the Matchappel system dispensed with.
For any further studies involving the MBE, an emphasis will have to be placed on overall machine/system reliability. To date, the MBE has only been applied at mines with worked shift availabilities of less than 70%, and regularly closer to 50%. Much higher average shift availabilities will no doubt better test the machine and associated ideas like the Matchappel conveyor system. Availability is undoubtedly a critical issue for further research.
In a single roadway, the MBE has demonstrated it can be used to advance the panel significantly faster than with shuttle cars. The difference between an MBE driven road, and a companion road with shuttle cars, will mean that the MBE road will eventually be working under single entry conditions, as there will be no nearbye cross-cut. This in itself provides production penalties, as ongoing services are more difficult (take more time) to provide. Despite this, there may be merit in considering tandem single entries, each using an MBE. One of these roadways will have to facilitate the drivage of cut-throughs and several possibilities exist for this.
Unfortunately, none of the mines examined use the MBE in conjunction with a truly continuous miner like the ABM20 or Joy Sump Shearer. ACARP should foster the trial of such.
This study has identified panel move time as a significant factor in overall productivity, and whose significance will increase dramatically as panels advance faster with devices like the MBE. This area needs research and development attention now if the industry is not to find itself lacking in the near future.