Effect of Stress Anisotropy on the Efficiency of Large-Scale Destress Blasting
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ORIGINAL PAPER
Effect of Stress Anisotropy on the Efficiency of Large‑Scale Destress Blasting Isaac Vennes1 · Hani Mitri1 · Damodara Reddy Chinnasane2 · Mike Yao2 Received: 7 February 2020 / Accepted: 12 September 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Large-scale panel destressing is a rockburst control technique that is used to create a stress shadow in the ore pillar to be mined. The technique aims to reduce the pillar burst proneness by deviating the major induced principal stresses away from the concerned zone of interest. The destress panels, situated in the pillar hanging wall, are choke-blasted with high explosive energy density, and the blast-induced damage in the panel is accompanied by stress dissipation and stiffness reduction due to fragmentation in the panel. These two effects are traditionally modeled holistically with stiffness and stress reduction factors α and β, respectively, applied to the destressed zone. This paper focuses on the interpretation of Phase 3 destress blasting results at Copper Cliff Mine (CCM) where a stress increase (rather than decrease) was detected in the ore pillar crown, while a stress decrease was recorded in the ore pillar sill (as expected). It is hypothesized that high mining-induced stress anisotropy in the pillar crown caused blast-induced fractures to propagate in the orientation of the major principal stress, a condition that would hinder the destressing effect in that orientation. To verify the hypothesis, a series of panel anisotropic rock fragmentation and stress dissipation factors are iteratively tested in a 3-dimensional back analysis of the Phase 3 destress blast. The analysis takes into consideration the stope extraction schedule per the mine plan to better replicate the mining-induced stress condition in the panel and the ore pillar. The results show good agreement with stress measurements taken in situ using borehole stress cells installed in the ore pillar prior to destressing. The paper discusses the implications of preferential fracture propagation orientation and how it might affect the efficiency of destress blasting. Keywords Destress blasting · Preconditioning · Rockbursts · Strainbursts · Numerical modeling Abbreviations CCM Copper Cliff Mine VRM Vertical retreat mining URM Upper retreat mining CCBM Compact conical ended borehole monitoring OB Orebody SC Stress cell
* Isaac Vennes [email protected] 1
Department of Mining and Materials Engineering, McGill University, Montreal H3A 0E8, Canada
Vale Canada Ltd, Copper Cliff P0M 1N0, Canada
2
1 Introduction Large-scale panel destressing has been successfully implemented in Canadian hard rock mines in the mid 2000s at Fraser Mine (Andrieux 2005) and Brunswick Mine (Andrieux et al. 2003), and more recently at Copper Cliff Mine (Vennes et al. 2020). The blast pattern in all these cases was dense, with large diameter holes (> 100 mm) yielding explosive energies exceeding 200 kCal/kg. This contrasts with the more common tactical implementati
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