Hangingwall surface subsidence at the Kiirunavaara Mine, Sweden

Large scale surface subsidence has been experienced at the Kiirunavaara mine since sublevel caving was implemented as a mining method. Surface disturbances are affecting part of the city of Kiruna, the railway, and the power station. Continuous and discontinuous subsidences characterize the hangingwall deformation, which is periodically monitored using surveying techniques and mapping of surface cracks. A historic review of subsidence prognoses has been carried out and the results compared with the actual condition of the hangingwall. The review showed discrepancies between different prognoses. In addition, limit equilibrium analyses indicated that break angles flatten while the mining depth increases. However, this tendency is not clear in the field where break angles show a large dispersion of values. By using surveying data, two different analyses have been performed. The time-dependent movements of the hangingwall have been described using time–displacement curves and strain analysis has been performed for different sections of the hangingwall. Three different stages of the time–displacement behavior have been identified and described. It has been concluded that extension strain can reach values which may damage civil structures before surface crack can be observed.

► Break angle prognoses show discrepancies with the break angles measured in the field.
► The hangingwall response to excavation resembles the behavior of rock slopes.
► The movement rate of the hangingwall was estimated by using surveying data.
► Horizontal strain after the outermost crack could damage sensitive strctures.