Determination of the effect of roof pressure on coal hardness and excavation productivity: an example from a Çayırhan lignite mine, Ankara, Central Turkey

Mechanized longwall mines require a systematic excavation schedule to control roof stress. Excavation sometimes becomes easier when the cutting cycle is interrupted and the face is subjected to in-situ strain, because the excavation machine may perform more efficiently. However, under those circumstances, it is important to determine the critical point at which this advantage overcomes the negative safety (high roof pressure) and productivity (long wait) aspects. This study was conducted in a retreating longwall underground mine in which a mechanized excavation system is used. To determine the most efficient extraction rate, time-dependent changes in the support pressures and coal hardness measurements made with the Schmidt hammer method were determined at the coal face. Thus, a time-dependent relationship between the hardness of the coal face and roof pressure was established. As a result of these analyses, the optimum waiting time before excavation was determined (for the mine in which the measurements were carried out) in terms of support safety and excavation productivity.