Large-scale sublevel cave mining unavoidably results in the rock mass around the orebodies being affected by caving and stress redistribution. Knowledge about the extent of areas that will not allow safe placement of infrastructure is essential for the planning process for deeper mining. This paper presents a case study from the LKAB Malmberget iron ore mine in which "infrastructure restriction volumes" were developed for guidance of where mining infrastructure such as ramps, shafts, etc., should not be located for future mining at depth. The methodology used involved simulating historic and future production in a mine-scale numerical model, containing relevant geology but no infrastructure. The mine-scale model simulates caving and material flow together with mechanical (stress and deformation) calculations in a coupled process. Stresses were extracted from the mine-scale model and applied to local models, built based on case areas with observed and documented damages from the mine. The local models were constructed with detailed geology and explicit infrastructure. Several criteria for predicting damage were tested and compared with mapping data from multiple locations in the mine. The most suitable criterion for prediction of damage that corresponds to infrastructure function being compromised was the Strength- Stress Ratio (SSR), which describes the "margin capacity" of the rock mass. This criterion was then applied to the mine-scale model to create restriction volumes for each year of mining down to a depth of 1900 m, corresponding to the depletion of currently known orebodies in the mine. The restriction volumes consider static (aseismic) loading only. Development of infrastructure inside the restriction volumes should be avoided or minimized, but in cases where developing infrastructure inside the restriction volumes is necessary, this should be done in a way allowing for future rehabilitation. For current infrastructure located inside the restriction volumes rehabilitation or alternative infrastructure plans should be developed.
KEYWORDS
Sublevel caving; numerical modelling, global-local modelling; strength-stress ratio
