Factors Influencing Rock Burst Hazard in Deep Copper Ore Mine, SW Poland

Abstract

Abstract In underground mines of copper ores, which are situated in Lower Silesia in SW Poland, the most common and dangerous threats pose seismic tremors and rock bursts. Copper ore exploitation is carried out in three mines, which are owned by KGHM Polish Copper JSC, i.e. Lubin mine, Rudna mine and Polkowice-Sieroszowice mine. Despite many rock burst preventive operations carried out over several decades of mining activity and aimed at counteracting seismic dynamic events, these phenomena have not been eliminated. The applied rock burst prevention measures only limit or mitigate the effects of seismic events. In mining, a concept of seismicity is used, which is defined as the tendency of an intact rock mass to seismic tremors induced by mining work in an area that was previously aseismic. Tremors and their results i.e. rock bursts affect not only excavations and underground infrastructure, but also the terrain surface. In the KGHM’s mines, seismic activity is monitored by the Mining Geophysics Stations. The number, coordinates and energy of tremors and rock bursts are registered, which helps determine the rock mass reaction to the adopted system and operation technology. The main purpose of the paper is to analyse seismic dynamic phenomena damaging mining excavations, i.e. rock bursts, in the Lubin mine, which took place from the beginning of the mine’s operation in 1975 to 2016 (over 41 years) and to identify and investigate geological and mining factors (parameters) facilitating the growth of seismic and rock burst hazards. The following factors (parameters) favourable for the occurrence of dynamic phenomena with damaging effects in excavations were taken into consideration: the seismic activity of the rock mass (spontaneous and provoked tremors), the deposit depth and thickness, geomechanical properties of rocks, exploitation systems, the method of elimination of mined-out space, the occurrence of gobs, tectonic disturbances and the life time of excavations. The results of the observation of selected parameters made it possible to determine the causes of rock bursts as well as to evaluate the impact of the exploitation system including the technology and rock burst prevention on seismic and rock burst hazard. Moreover, seismic activity of the mining division with the highest number and energy of rock bursts was analysed. The effectiveness of rock burst prevention measures used in this division was assessed too. The results of the analyses indicated some interdependencies between factors that may affect the phenomena discussed.