The 4th International Symposium on Mine Safety Science and Engineering (ISMSSE2018)

278 / 2018-04-25 21:27:34

Volumetric changes in the focal areas of seismic events corresponding to destress blasting

Destress blasting, Seismic event, Volume changes, Stress release

Mine Dynamics Disaster > Rock burst impact

The typical development of total volumetric change in the focal areas of seismic events, corresponding to destress blasting, is characterised as an explosive phase followed by an implosive phase and with alternating additional phases following on from that. In a few cases, a non-typical development of volumetric change was identified, where the first phase was implosive and the second phase, explosive. This development is mainly typical for induced seismic events recorded during mining, not for destress blasting. Seismic events were recorded during longwall mining in the Czech part of the Upper Silesian Coal Basin, where the destress blasting technique is used as an rockburst prevention active measure. Kinematic source processes in the focal areas of selected seismic events were analysed by the seismic moment tensor inversion method, as well as by studying geomechanical rock mass conditions at the localities of the seismic events. The main goal of the analysis was to attempt to identify the reasons for non-typical development of volumetric changes in these cases. Volumetric changes were analysed for seismic events with energy greater than 104 J, recorded in the period of time from 1993 to 2009 (1109 events). 80% (891) of the recorded seismic events were induced seismic events that were registered during longwall mining and 20% (218) corresponded to destress blasting events. Research shows that the main reason for the non-typical development of volumetric changes in the focal areas of seismic events is an association with destress blasting in the rock mass, which is very close to rock mass overstressing. The detonation of explosives in boreholes, which would dominate the first phase of volumetric changes, probably obscured stress release in the rock mass, as manifested in the first implosion phase of the volumetric changes in this case.