Prediction of ground surface collapse by instrumental observation data on rock mass movements during underground mining

Using the data of long-term surveying at the Saranovsky chrome iron ore deposit, movements of rock mass were analyzed with a view to identifying potential early signs of ground surface collapse. The research findings are unique as one of the instrumental observation series was accomplished on the eve of the ground surface sinking above non-backfilled voids of earlier stoping. It was found that the test area experienced vertical alternating movements, and sinking was preceded by upheaval of ground surface. However, the further analysis revealed no clear cause-and-effect between the event and insufficiency of its study. The subsequent research identified a local cluster of rock mass subsidences at gradually increasing velocities, which showed up a few years before the sink appeared on ground surface above its initiation source. The absence of this cluster zone in the period before the collapse is explained by the damage of check points in this site. Finally, the conclusion is drawn that in certain geological conditions, deformation processes are localized and manifest no visible signs of impact on the enclosing rock mass and ground surface. Manifestations of these processes from the instrumental observations concentrate directly in the local area of their development, which should be taken into account in the analysis and prediction of movements. It is emphasized that the existing and new criteria of hazardous deformation processes should be corrected and updated for geomechanical monitoring of mineral mining objects.