Mining-Induced Deformation in the Malmberget Mine

The Norra Alliansen orebody of the Malmberget sublevel caving mine consists of iron ore interspersed with biotite schist and granitic inclusions. The schist is squeezed between the ore and the host rock and in direct contact with the ore along the majority of the length of the footwall. The schist exhibits high deformation when exposed to stress. SMART cable bolt roof deformation measurements are re-analyzed to draw conclusions regarding the patterns of deformation in the mine. Each bolt's head is placed at the origin of a spherical coordinate system and the radius and inclination angle between the bolt and every production blast occurring during the bolt's recorded lifetime are calculated. The deformation experienced by each instrument is investigated by comparing the long-term recorded movements with the developed geometric variables. Patterns of deformation magnitude and rate are found with respect to production-blast distance and inclination angle, instrument location, rock quality designation, and likely mining-induced stresses. Results show that deformation magnitude tends to be higher when driven by production blasting occurring on the production level above the instrumentation when accounting for the effects of distance, but average deformation magnitude for very-near production blasts tends to be higher than that for production blasts occurring directly above the instrument. Correlations also exist between the measured RQD, estimated rockmass parameters, and the measured deformation. Empirical evidence allows the identification of six scenarios which account for 91% of the recorded high-deformation-rate events. These scenarios help determine which production activities are most likely to cause high deformation rates.