Control of rockburst risk in hard coal longwall mining - A case study

Rockburst represents a very dangerous phenomenon in the Upper Silesian Coal Basin (USCB). The rockburst problem relates to the natural and mining conditions in the rock mass. It is very difficult to decide which of the factors prevails, but we generally assume that the existence of competent adjacent rocks in the roof of the seams and incomplete seam extraction in the overburden, cause irregular stress distribution in the rock mass and stress overflow in those regions with the highest stress concentration. Destress blasting in overlying competent rocks is a very important rockburst control technique. The case study describes the control of rockburst risk by destress blasting in an example of the longwall of the Czech part of the USCB. Destress blasting, in the competent overburden of the exploited seam, was applied as the main rockburst prevention method. Groups of boreholes were fired ahead of the longwall face with explosive charges of up to 4500 kg during the longwall mining of the thick coal seam. An analysis of the effectiveness of stress release following destress blasting and generally, during the course of mining was realized. Despite its rarity, rockburst in the longwall face was induced by the applied destress blasting during the course of longwall mining. The authors evaluate the causes and effects of the induced rockburst from in situ stress and deformation measurements. The case study presented confirms that destress blasting is a very important mine safety tool that contributes to the reduction of rockburst hazard.