Shafts and rock mass strength : Calibration using numerical models

Sammanfattning: Orepasses and ventilation shafts are examples of mine infrastructure that are subjected to increasingstresses as the production in the Kiirunavaara mine moves to deeper levels. Falloutsand damages in these kind of excavations are already occurring and the problem can be expectedto increase in the future. Information about the rock mass properties is necessary in order to predict the extent of stressinduced failures in the future. The main focus of this thesis was to calibrate rock mass strength parameters by using numerical models in combination with observations of actual damages. Orepasses are affected by wearing from falling rock, which can be difficult to take into account in a numerical model. Damages from ventilation shafts were therefore chosen as input in the numerical modeling. A material model for brittle failure was used in the calibration. Damage mapping of several ventilation shaft was done and damages with typical stress-induced characteristics were chosen for the calibration of strength parameters. Most of the calibration calculations were successful. Final results for each parameter were calculated as mean values from all successful calibrations. The result from the calibration was thereafter used as input values in a prognosis calculation for stress-induced damages in future mining. Two ventilation shafts with varying distance to the orebody were analyzed. The stress situation for future mining was simulated for two upcoming production levels, 1165 and 1223. The prognosis results showed that stress-induced failures will increase in both quantity and severity. The modeling results showed stress-induced failures with a depth up to 50 cm. It was also concluded that the horizontal distance to the orebody has a large influence on the occurrence of stress-induced failures in ventilation shafts.