Application of Seismic Monitoring and Numerical Modelling in the Assessment of Possibility of Seismic Event Occurrence in the Vicinity of Ore Remnant

Abstract

Seismic and rockburst hazard is one of the basic problems associated with deposit exploitation in many underground mines. Rockbursts are responsible for many mining accidents, and their effects, which include damaged excavations, destroyed equipment and machinery, generate financial losses and disrupt the operational continuity of the mining facility. Dynamic phenomena occurrence is one of the major natural hazards in Polish underground copper mines in the Legnica-Glogow Copper Belt (LGCB). The degree of seismic hazard in the LGCB results, among others, from the great depth of the copper deposit exploitation, high-strength rock layers in the roof strata and the ability of rock mass to accumulate elastic energy, as well as from an increasing amount of mining works to be carried out in difficult geological and mining conditions, for instance in the vicinity of remnants. The purpose of this paper is to show the influence of ore remnant on the possibility of seismic event occurrence by seismic activity analysis and numerical modelling. The possibility of using numerical modelling to back-calculate the occurrence of a seismic event due to sudden shear rupture is also presented. Analyses were conducted for the case study of the Polkowice-Sieroszowice Polish underground copper mine for the room-and-pillar mining system with room deflection. For the selected mining field, quantitative analysis of seismic activity was performed in connection with the assessment of the mining situation in this field. The location of tremor epicentres in the context of the existing geological and mining situation was also analysed, with special attention paid to the impact of remnants and dynamic phenomena in their vicinity. Subsequent investigations focused on the back analysis of deposit exploitation by room and pillar mining system with roof deflection in the selected mining field. Numerical simulations were conducted in a plane deformation state by means of Phase2 v. 8.0 software, which is based on the finite element method. The results of seismic and numerical analyses show that undisturbed rock remnants may have a negative impact on the seismic and rockburst hazard in the mining field. The analyses also show that on the edge of a rigid remnant, sudden fracturing of roof strata may occur, as a result of exceedance of shear strength (shear rapture). This may cause a high-energy mining tremor, and under appropriate conditions, may result in a rockburst phenomenon.