The underground coal mine pillar development cycle consists primarily of three sets of interdependent and synchronised cycles, i.e., the coal cutting cycle by a continuous miner (CM), the support cycle by a roof bolter and the coal transport cycle to the boot end by a shuttle car. Coal cutting by a CM is generally not seen as a constraint as, in almost all cases, the capacity of the CM far exceeds the demand placed on it. Therefore, in essence, the pillar development process can be either transport constrained or support constrained.
Using a discrete simulation model, it was shown that for a case study mine a CM configured with two bolting rigs was support constrained when the distance from the boot end to the face was short. It was suspected that as the distance from the face to the boot end increased and development would change from being support constrained to transport constrained. For this case however, introduction of additional bolting rigs did not change the development rate significantly with an increasing distance from the face to the boot end, thus confirming the initial configuration of the mine was entirely support constrained, Simulation of a bolter-miner configuration with six bolting rigs and concurrent bolting indicated that such a system is a transport constrained.
With the introduction of a continuous haulage system (CHS), a bolter-miner configuration with six bolting rigs and concurrent bolting, changed the system to support constrained. This maybe explained by the fact that a CHS has a much higher transport capacity than a shuttle car. The simulation results showed an approximate 25% reduction in hours to develop five pillars using a CHS instead of two shuttle cars.
The paper discusses additional simulated results of a series of two-heading roadway developmetn scenarios to demonstrate the Theory of Constraints implementation methodology.