Powered support selection for longwall workings in dynamic load conditions

Currently in Poland hard coal is mined in two Coal Basins namely Upper Silesian and Lublin. In Poland, there were 30 underground hard coal mines that produced 72.5 million tons of coal in 2014. For underground hard coal (steam coal and coking coal) seam extraction, the longwall method is used and retreat longwalls with natural roof caving in the gob are the most common. Currently it is estimated that about half of the hard coal output in Poland originates from seams located in areas of rock burst hazard. In this paper, the most important data concerning the geological and mining conditions in Polish hard coal collieries are presented with particular emphasis on tremors, rock bursts, and fatalities. Moreover, the article shows information about seismic events which occurred between 2003 and 2012 in underground mines belonging to one of the coal companies in Poland. In addition, negative consequences of those dynamic phenomena in the longwall workings are described. In order to avoid damage of powered supports in geomining conditions where dynamic phenomena occur, different types of protective means are applied. In the paper the methodology of assessing the powered support yield ability is described.