Use of an integrated finite/discrete element method-discrete fracture network approach to characterize surface subsidence associated with sub-level caving

The LKAB Kiruna sub-level cave mine, located in Kiruna, Sweden, is one of the most well studied sub-level cave mines. Due to proximity of the city to the hanging wall, the mine has developed a comprehensive surface deformation monitoring program which is perhaps unparalleled in the mining industry. This surface monitoring scheme provides an excellent data source with which to constrain numerical modelling. In this study, a finite/discrete element modelling approach coupled with a discrete fracture network (FDEM-DFN) is utilized to analyse the Kiruna hanging wall surface subsidence with an emphasis on investigating the influence of discontinuity persistence and spacing. The FDEM-DFN data interpretation uses a variety of novel approaches including time-displacement hanging wall deformation characterization, numerical inverse velocity analysis and virtual hanging wall inclinometer simulation to improve our understanding of the extent and mechanism of hanging wall failure with mine advance. The simulated displacements correspond closely to the actual field data, illustrating the ability of the proposed approach to reproduce sub-level cave behaviour. Three distinct time-displacement phases namely: regressive, progressive and steady state are observed in the FDEM-DFN models. The paper also reviews the potential application of the inverse velocity method and virtual inclinometers in characterizing sub-surface brittle failure associated with sub-level caving.