Tunnel face preconditioning using destress blasting in deep underground excavations

Abstract

The controlled use of explosives for the purpose of introducing fractures to the rock material in deep underground mining and tunneling activities is considered one of the tactical approaches to alleviate the mining induced rockburst potential at great depth. Rockbursts, which are associated with sudden release of the strain energy stored in brittle rock, are considered safety risks for the personnel and lead to production disruption imposing economic threats. Preconditioning of the rock mass ahead of a tunnel development face can be achieved using destress blasting techniques in order to dissipate the stored strain energy in the stress concentration zones by damaging the rock. Such technique will eventually transform the stress states ahead of the tunnel face where the magnitude of the peak stresses is reduced and pushed further away from tunnel face. This paper studies numerically the extent of the blast-induced damage zones in underground excavation activities in the presence of anisotropic principal stresses. The effectiveness of the current destressing blast patterns is investigated and the resulted damage zones and the stress states before and after destressing in studied. A new destress blasting pattern is introduced in which the blast-induced damage zone is capable of effectively transforming the stress states ahead of a tunnel development face.