This research seeks to apply the Strain Effective Radius Factor developed by Milne and Snell (2018) as an empirical technique to predict the geometry at which hanging wall instability may occur. The prediction of an unstable geometry is based upon a relationship between the magnitude of strains measured by a multi-point borehole extensometer and the changing geometry of the hanging wall.
To test the SERF method, extensometers were installed in stope hanging walls of at a narrow vein gold mine. Deformation data was collected from the extensometers through the undercutting and subsequent ring blasts of a stope. As rings were blasted and mining extraction approached the extensometer location, a compressive strain in the hanging wall was noted. After the extensometer was undercut, an indicated tensile response that appeared to be initially elastic followed by non-linear deformation as mining progressed past the extensometer location. The relationship between the non-linear deformation and the excavation geometry were plotted to predict a stope geometry at which hanging wall instability might occur. The compressive and apparent initial tensile response were also compared to expected stress levels in the mining area.