Induced micro-seismicity and mechanical response during the experimental flooding of an iron ore mine

Overview & Synopsis

In order to understand the impact of flooding on mining collapses and its relationship with the micro-seismic activity, a controlled experiment of cavity flooding was performed in an underground iron mine. 134 micro-seismic events (magnitude < 0) were recorded during the experimental flooding. The micro-seismic activity showed a correlation with the water injection evolution in the cavity suggesting that micro-seismic activity was triggered by the stress modification induced by water introduced in the cavity. Two main processes are suggested: a) micro-seismic events (class 1) forming a group of perfect multiplet families and a frequency spectrum higher than 200 Hz; these events were triggered by the reactivation of pre-existing fractures; b) micro-seismic events (class 2) not forming a group of multiplets families with a frequency spectrum lower than 200 Hz; these events would be the result of complex interactions between the increase in elastic stress and the cumulative effects of increased pore pressure. The largest seismic events were triggered only during the water rise in the cavity suggesting that the water rise phase is a particularly sensitive trigger for the largest mechanical instabilities