Published in the March 2011 Australian Longwall Magazine

Best practice operators are achieving an average 5 metres per operating hour over the gateroad pillar cycle with shuttle car haulage, ranging from 8mpoh at commencement of the pillar cycle to 3mpoh at conclusion of the cycle.

Studies carried out by Richard Porteous have projected that sustained rates of 6-7mpoh are achievable with bolter-miners and a balanced or matched cut/load/support/coal clearance system employing two shuttle cars, improving to sustained rates of 6-8mpoh with the further adoption of self-drilling bolts.

At a target rate of 10mpoh shuttle cars would be required to travel between miner and conveyor 20 times in each direction per hour. It is estimated shuttle cars travel a distance of 86-90 kilometres to complete each pillar cycle, often over adverse floor conditions. It is therefore difficult to envisage shuttle cars being able to sustain an advance rate of 10mpoh unless bunkering, auto-steering and rapid loading and unloading systems were employed to reduce cycle times.

While a remotely controlled shuttle car operating system was first developed at Tahmoor in the mid-1990s as part of a remote mining system employed for outburst mining, no further development or commercialisation of a remote control system for shuttle cars has been undertaken since that time.

Further, despite positive advances being made to operator ergonomics, the continued utilisation of manned shuttle cars remains both a serious occupational health issue and a performance limiting factor.

The underground metalliferous sector has developed and introduced remote control systems for diesel haulers, and has demonstrated that higher operating speeds and reduced cycle times can be achieved, together with reduced running and maintenance costs.

Given the projected capital costs of a high capacity continuous haulage system at more than $15 million, the current widespread adoption of shuttle cars and the industry’s capacity, ability and willingness to fund development of a fully integrated high capacity roadway development system, development of an auto-steering and remote control system for shuttle cars is warranted to address the occupational health issue, as well as providing a building block towards a fully automated and remotely supervised development system.

A distinct disadvantage of perpetuating the use of shuttle cars is the space utilisation issue associated with such bulky systems, particularly as development rates improve and haulage frequencies increase through introduction of other technologies and improved management practices.

Roadway development

In the 2005 review of current Australian roadway development practice considerable interest was expressed by industry participants in the subject of roadway profile, that is, formation of a rounded, self supporting roadway profile at the roof/rib interface.

While geotechnical engineers argued that the sedimentary nature of coal seams did not offer the same support mechanism as more competent homogeneous strata, operators reported many instances whereby formation of such a rounded roof/rib profile with machines such as borer miners, the Joy Sumps Shearer, Eickhoff Easi-miner and other full face development machines resulted in improved strata support conditions.

A number of mines using conventional wide head continuous miners currently experience extensive deterioration of the roof at the roof and rib interface, and are forced to overlap the roof and rib mesh and install bolts in close proximity to the interface in order to control this deterioration.

Any requirement to bend and overlap mesh challenges the development of automated mesh handling devices.

Again, a question needs to be asked – can formation of a rounded roadway profile at the roof and rib interface provide any level of improved strata control, particularly in regards to obviating the need to overlap roof and rib mesh?

If adoption of wider gateroads was considered to have merit from a longwall operations perspective it would then be necessary to develop strata support systems that enable the roadways to be supported effectively from both a development and a longwall extraction perspective.

Wider gateroads may require an increase in the number of roof bolts required if bolt lengths are maintained, potentially resulting in lower development rates unless additional bolt installation capacity is installed. Geotechnical advice suggests that roadway widths could be readily increased to 6.5m in many instances without a significant or undue increase in support requirements.

Adoption of wider roadways and maintaining continuous miner chassis configurations at current widths may provide additional real estate in which to increase the number of bolting rigs, effectively increasing the support density per bolting cycle.

Alternatively, wider roadways may be more effectively supported by installing fewer but longer bolts or tendons, with the additional real estate provided by wider roadways and current continuous miner widths being utilised to install automated tendon installation systems.