Assessment of Seismic Hazard in Relation to Rock-Burst Prevention Modifications in KGHM Polish Copper JSC Polkowice - Sieroszowice Mine, Poland

The Polkowice-Sieroszowice mine is one of three underground copper ore mines in Poland. These three mines belong to KGHM Polish Copper JSC, excavating one of the largest copper ore deposits in the world. The deposit is situated in the south-western part of Poland in the Lower Silesia province. Due to the specific and difficult geological-and-mining conditions in the three mines, seismic events occur which often result in an excavation serious damage defined as the rock-burst or elastic recovery. Such dynamic phenomena have been occurring since 1972 and have posed the most dangerous natural threats in underground workings. Therefore, the mining technology has to take the account of seismic hazard prevention. Numerous preventive measures adjusted to the conditions prevailing in the given operating field have to be applied so that the hazards can be mitigated, fought or limited. The appropriate choice of prevention activities must be preceded by measurements and observations, which constitute different methods for identifying, predicting and assessing the condition of the rock mass as well as for evaluating the protection effectiveness. In the Polkowice-Sieroszowice mine the rock-burst prevention involves: assessment of rock mass state and active, technological, and organizational-technical methods for combating the hazard. The active prevention consists in blasting works which provoke the rock mass to distress itself and thus to reduce its capability to accumulate elastic energy. The technological prevention embraces yielding the edges of the walls and pillars in the place of development, the extraction of the deposit with a wide opening of the front and the adjustment of the size of the technological pillar to the local geological and mining conditions. The organizational-technical measures introduce after-blasting waiting time and high hazard zones where the number of employees should be reduced. The influence of changes and improvements in the prevention activities on the seismic hazard was analysed and determined. The effectiveness of prevention methods was assessed in connection with their modifications, which concerned certain elements of active methods, the pillar size changes and alterations in the frequency of rock mass observations. Most of these modifications resulted from the operational progress and had a little impact on the seismic activity. Nevertheless, the effectiveness of such alterations was calculated. The research was carried out for one mining division in the Polkowice-Sieroszowice mine over the period of 2013-2015 years. The increase in the effectiveness of seismic/rock-burst prevention in most cases resulted in reduction of seismic activity.